OPC applications
TP1 | Mercury Science and Exploration
Introduction
Mercury’s surface is characterized by large and well-preserved impact basis. They represent important records regarding the magnitude and timing of the “Late Heavy Bombardment” in the early inner solar system. It has been suggested that Mercury and Moon had the same early impactor population based on their similar crater size frequency distributions [1,2]. In this study we investigated the basins using complementary topography and gravity data sets derived by MESSENGER [3,4]. Gravitational data in combination with the surface morphology of the basins may help improve our understanding of their formation processes and alterations with time. Gravity anomalies hint at complex interior structures, such as mass and density distributions in the upper crust of the planet, which is beneficial for identifying highly degraded or buried basins.
In this study, we present an inventory of basins larger than 150 km, for which we introduce a classification scheme according to morphological and gravitational signatures.
Methods and data sets
The topographic digital terrain model (DTM) used in this study was derived by the Mercury Dual Imaging System (MDIS), involving a narrow-angle- as well as a wide-angle camera [3]. Gravity data data of the MESSENGER spacecraft, which resulted in a gravity field model with a resolution of degree and order 160, equivalent to approximately 28 km in the spatial domain [4].
Fig 1: DTM of Mercury’s topography. Circles mark the identified basins.
Results
Our preliminary basin inventory hosts 311 basins (Fig.1). A clear correlation is noticed between the topography and gravity data, in particular impact basins are well detectable in both data sets. Their global distribution is non-uniform. Around 60% of basins are located on the western hemisphere. This asymmetric pattern may be caused by (I) lateral thermal variances of the crust [1], (II) synchronous spin- and orbital periods of the planet in its early history, which later changed to its presently observed 3:2 spin-orbit resonance [2], (III) resurfacing events that includes the northern smooth plains and following flooding of existing basins on the eastern hemisphere, which would eventually bury smaller complex basins.
With increasing diameter basins were found to show more complex gravity- and topography signatures. Basins with smaller diameter (<160 km) display a central peak. With increasing size, the morphology changes to a peak ring in the center. The transition from peak ring to multi-ring basins is suggested to occur at 350 km as is attested by a distinct change in the gravitational signal. The gravity disturbance remains mostly in strong negative values. This value shifts to a positive one for basins larger than 350 km.
High positive gravity signals were also recognized in the Bouguer anomaly map. Some basins (>350 km) possess a positive Bouguer anomaly in the basin center surrounded by a negative anomaly annulus (bullseye pattern) (Fig 2). Gravity data are reflecting mass/density deficits and excesses in the planet’s subsurface structures. The high mass and density concentrations may be caused by an uplift of mantle material after the crater excavation phase [5]. The excavation was followed by an isostatic adjustment caused by cooling and contraction of the melt pool. Subsequently, crust is expected to be thinner.
Fig 2: Left: Profile of Bouguer anomaly, Right: Bouguer anomaly map; showing positive strong anomaly in center surrounded by negative annulus.
However, basins with small diameter (<200 km) were found to show strong positive anomalies as well, that indicate a mantle uplift after their formations. Due to limited data resolution (particularly in the south) the localization and accuracy of the Bouguer anomalies is not certain.
Other 208 basins where identified, but could not be characterized in detail due to their high degradation state (rim <50%). Most of these are filled by secondary material. Future data with improved resolution would be required to verify these results.
We investigated the amplitude of Bouguer anomalies in the basin centers and surroundings as a measure of crustal thinning, which may hint at basin relaxation state. Lunar observations showed, that young basins with large diameters should contain strong positive anomalies because of limited relaxation due to high viscosity of a cooler planet [6]. In contrast, a less pronounced gravity anomalies hint at higher relaxation due to lower viscosity and a hotter crust in the planet’s earlier history (Fig 3).
Fig. 3: Bouguer anomaly contrast from rim to centre versus rim diameter. Basin classes: b_deg- degraded basin (<50% rim preserved), centr_peak- central peak basin, peakr- peak ring basin, com- complex basin (>50% rim preserved).
Acknowledgements
This work is supported by the Deutsche Forschungsgemeinschaft (SFB-TRR170, A6).
References
[1] Orgel et al., 2020, Re-examination of the Population, Statigraphy and Sequence of Mercurian Basins: Implications for Mercury’s Early Impact History and Comparison with the Moon, J. Geophys. Res. 125(8), doi:10.1029/2019JE006212
[2] Fassett C. I., et al., (2012), Large impact basins on Mercury: Global distribution, characteristics, and modification history from MESSENGER orbital data, J. Geophys. Res. 117, E00L08, doi:10.1029/2012JE004154
[3] Preusker et al., Towards high-resolution global topography of Mercury from MESSENGER orbital stereo imaging: A prototype model for the H6 (Kuiper) quadrangle, Planetary and Space Science 142 (2017) 26-37
[4] Konopliv et al., The Mercury gravity field, orientation, love number, and ephemeris from the MESSENGER radiometric tracking data, Icarus, Volume 335, 2020, 113386, ISSN 0019-1035,https://doi.org/10.1016/j.icarus.2019.07.020.
[5] Wieczorek, M., The gravity and topography of terrestrial planets, Treatise on geophysica, 2006
[6] Neumann et al., 2015. Lunar impact basins revealed by Gravity Recovery and Interior Laboratory measurements. Science Advances 1(9), 1-10.
How to cite: Szczech, C. C., Oberst, J., and Preusker, F.: Classification of Mercury’s Impact Basins, Based on Topography- and Gravity Signatures in MESSENGER Data, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-595, https://doi.org/10.5194/epsc2022-595, 2022.
TP2 | Paving the way to the decade of Venus
Introduction:
Within the next decade, there are plans to carry out at least three space missions - Envision, DAVINCI+ and VERITAS - with which we could significantly broaden our current knowledge about Venus from the astrobiological point of view. A great supplement of the in-situ research carried out on Venus are the experimental tests carried out on Earth in a specially designed testing chamber with the reconstructed conditions encountered on Venus clouds. The need for such research, both in situ by probes and spacecraft on Venus, as well as in Earth's research laboratories, is suggested by the latest research results and formulated research hypotheses regarding potential life in the lower part of Venus clouds (at an altitude of 47.5-50.5 km above its surface) [1]. On the other hand, 3D-climate models indicate that this planet for a long time could have been characterized by an inhabited climate and have an ocean of water on its surface [2]. The discovery of phosphine in the clouds of Venus may also indicate the presence of microorganisms in the clouds of Venus [3].
Results and discussion:
Spectrophotometric UV-Vis-NIR tests of Acidithiobacillus ferrooxidans - strain 583 DSM have been carried out and the experimental data that have been obtained were compared with their counterparts characteristic of Venus clouds on the same wavelength [4]. The obtained dependence incident radiation wavelength vs. the transmittance for the studied bacteria Acidithiobacillus ferrooxidans, strain 583 DSM and Venus show similarity for specific wavelengths λ, which may indicate the potential existence in the clouds of Venus of microorganisms that are analogues of the terrestrial bacteria Acidithiobacillus ferrooxidans, strain 583 DSM with similar physicochemical properties. Further research of different types of acidophilic bacteria in the testing chamber with the reconstructed conditions encountered on the lower layer of Venus clouds will allow for the identification of further Earthly analogues of microorganisms potentially inhabiting Venus clouds.
References:
[1] Limaye S.S. et al. (2018) Astrobiology, 18, 1181-1198.
[2] Way M.J et al. (2016) Geophys. Res. Lett., 43, 16,
8376-8383.
[3] Greaves, J.S. et al. (2021) Nature Astronomy, 5, 655-
664.
[4] Kuiper, G.P. (1969) Comm. Lunar Planet. Lab., 101, 1-
21.
Figure 1
Scanning electron micrographs of Acidithiobacillus ferrooxidans, strain DSM 583.
How to cite: Stryjska, A., Słowik, G., and Dąbrowski, P.: Could Acidithiobacillus ferrooxidans be analogs of microorganisms potentially inhabiting Venus clouds?, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-941, https://doi.org/10.5194/epsc2022-941, 2022.
TP3 | Forward to the Moon: The Science of Exploration
Introduction
Lunar robotic and human exploration efforts are ramping up, as exemplified by ongoing studies and missions from different space agencies, such as NASA and ESA with the Artemis program (e.g. NASA, 2020). In this scenario, the identification of potential resource deposits is of primary importance for the future exploration of planetary bodies (e.g. Lewis et al., 1993; van der Bogert et al., 2021). One of the most important deposits on Earth, but not well studied outside our planet, are the intrusive igneous processes and their derivative features. This work is the first step in ongoing research to evaluate the potential of this kind of geological setting on the Moon. We conducted a detailed analysis of an intrusive complex named Valentine Domes.
The Valentien Domes are located at the west margin of the Serenitatis Basin (30.69° N, 10.20° E). According to Wöhler and Lena (2009), they consist of two different edifices, a small one to the north and a big asymmetric dome 70 km wide to the south. The same authors identified a large fault at the east side of the bigger edifice, indicating that it originated as a laccolith (Schmiedel et al., 2017).
Data
In order to conduct the geomorphological and tectonic interpretation of the zone, we collected and processed 23 images taken by the Narrow-Angle Camera (NAC) onboard the Lunar Reconnaissance Orbiter (LRO). A high-resolution stereo-derived DEM was also generated using the Ames Stereo Pipeline (ASP)(Beyer et al., 2022). We also used some basemaps of the Moon, such as a global visible mosaic made with takes from the Wide Angle Camera (WAC), and a digital elevation model (DEM) derived from the Kaguya mission.
We coupled the prior analysis with mineralogical information derived from two hyperspectral cubes taken by the Moon Mineralogy Mapper (M3), onboard Chandrayann-1.
Results
Figure 1 shows the geomorphological map of the zone.
The area is dominated by lava flood plains that show variations in their albedo. Darker lavas accumulated close to the rim of the basin, while in the centre of the Serenitatis and Imbrium basins the lavas have a lighter tone. The two domic features identified by Wöhler and Lena (2009) lie close to the rim of the basin, but we identified what looks to be a third dome to the south of the principal structure. This newly identified dome has a maximum altitude of 90 meters and it steeps gently to the surroundings. No faulting is visible near the dome, which leads us to classify it as a domed laccolith (Schmiedel et al., 2017).
The uplands located on the rim of the Serenitatis Basin can be divided into Hilly materials (Him) and more dissected Hummocky materials (Hum). These materials at a first glance appear similar to a handful of small mounds located inside and around the Valentine Domes, this led Lena et al. (2018) to describe these features as kipukas from the floor of the basin. From the analysis using data from M3, we found that there is an apparent difference in composition between these mounds and the Him and Hum units. The units of the rim seem to have a major amount of plagioclase, which could point to a genetic difference between them and the mounds inside de domes. Thus, we mapped these features as different units: Secondary domes (Sd) and Secondary linear features (Slf).
We identified linear rilles crossing the main structure dome and the newly discovered dome. These lineations cross both domes almost by their centre, and in the case of the main dome, the rile is weakly aligned with the secondary domes inside it.
Figure 1: Geomorphological map of the Valentine Domes and northwest Serenitatis Basin.
Discussion and conclusions
The discovery of a new dome south of the principal structure could imply that the Valentine Domes complex is more intricate than previously thought. This is supported by the presence of linear riles crossing the domes, which according to Head and Wilson (1992), points to the existence of stagnated dykes not far beneath the surface. The secondary domes and the thrust fault cutting the main structure are hints that plutonic rocks could be located on the surface, alongside useful mineralizations.
Acknowledgments
This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 101004214.
How to cite: Suarez Valencia, J. E. and Pio Rossi, A.: Geomorphologic mapping of the Valentine Domes in the Moon, intrusive domes, and their mineral resource potential, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-923, https://doi.org/10.5194/epsc2022-923, 2022.
TP4 | Mars Surface and Interior
Introduction: Despite the large amount of information from orbital and in situ missions, the characteristics and evolution of Mars’ early climate are still widely debated among the scientific community. Morphological evidence dating back to about 3-4 billion years ago, such as valley networks [1], and the presence of several hydrated minerals [2] seem to indicate that Mars once had a “warm and wet” climate with abundant water on the surface and possibly even an ocean in the northern lowlands [1-3]. These conditions eventually changed through time leading up to the hyperarid and cold planet we observe today.
The area of Meridiani Planum (MP), located SW of Arabia Terra, is well known for retaining multiple evidence of past aqueous activity [4] and a varied hydrated mineralogy [5]. The majority of the terrains exposed in MP formed at the Noachian-Hesperian boundary [6], that is between two important epochs of Mars: the Noachian (4.1-3.7 Ga), where most of the evidence for water is found, and the Hesperian (3.7-3.0 Ga), which is characterized by increasingly water-limited conditions. Constraining the potential water environment at the NH boundary is fundamental to understand Mars’ early climate and its evolution.
In this study, we select 7 craters in Northern MP (figure 1) showing evidence of NH sediment infillings with hydrated materials (e.g., clays and sulfates) to assess in detail the stratigraphic sequence of the mineralogical units and understand their origin and diagenetic history. The craters are roughly aligned SE to NW following the general slope of the area from the highlands to the lowlands. If Mars experienced a “warm and wet” period, MP would represent a transition zone between the subaerial alteration environment of the highlands and the subaqueous environment of the Martian ocean. Therefore, the area would be easily affected by climatic changes whose evidence should be retained in its sedimentary sequences.
We show here some preliminary results from 2 out of the 7 craters selected for the study:
1) a 15-km-wide crater named Mikumi, centered at Lat. 2.45°N, Lon. 359.96°E;
2) an 18-km-wide unnamed crater centered at Lat. 4.25°N, Lon. 2.85°E.
Figure 1: THEMIS daytime image of Meridiani Planum. Selected craters are evidenced with points. Name (if given) and coordinates of the center for each crater are also indicated with a label. Most of the craters are unnamed. The arrows indicate the two craters described in this abstract.
Datasets and methods: We investigate the mineralogy of the craters’ terrains through CRISM [7] hyperspectral data cubes mainly in the range 1.0-2.6 μm. This interval retains part of the key spectral features of primary rock-forming minerals, which constitute the Martian crust, and of most minerals produced by secondary processes such as aqueous circulation and alteration (e.g., clays and sulfates). MOLA, THEMIS, CTX and HiRISE data are then used for morpho-stratigraphy and camera imaging.
Results: Two types of clays (smectites) with different Fe/Mg content, polyhydrated sulfates and monohydrated sulfates are observed in both craters (figure 2). Fe/Mg-clay spectra (e.g., nontronite and saponite) show absorptions at around 1.4, 1.9 and 2.3 μm with additional overtones at 2.4 μm. The exact position of the 2.3 μm feature depends on the relative Fe/Mg content in the clay mineral. We find some areas with clays richer in iron (e.g., nontronite), showing this feature centered at 2.305 μm, and clays richer in magnesium (e.g., saponite) where the absorption is centered at 2.310-2.315 μm. In Mikumi crater, polyhydrated sulfates (Mg sulfate) and monohydrated sulfates (kieserite) are detected stratigraphically below the clay-bearing layer. For the unnamed crater, the stratigraphic relationship of the units is still to be investigated.
Figure 2: (top) CRISM spectra of detected mineralogy. Fe/Mg clays (smectites) are from Mikumi crater, mono and polyhydrated sulfates are from the Unnamed crater. The spectra are extracted from FRT0000BEF5 and FRT00009B5A TRR datasets respectively. (bottom) Laboratory spectra of clays and sulfates from the CRISM spectral library [8] (Mg Sulfate ID: CJB366; Kieserite ID: F1CC15; Saponite ID: LASA51; Nontronite ID: NCJB26).
Discussion and conclusions: Clays and sulfates on Mars appear to have formed at different times and under different climatic conditions [9]. Clays are usually associated to Noachian terrains and may have formed under alkaline conditions in a “warm and wet” ancient Mars, whereas sulfates are typically associated to Hesperian surfaces and may have formed under a dryer and more acidic environment. Therefore, sulfates are expected to be found stratigraphically on top of clays, as they should have formed later in Mars’ history. However, this distinction between a clay-rich Noachian and a sulfate-rich Hesperian oversimplifies the history of the aqueous chemistry and climate of Mars especially near the NH boundary.
Our analysis suggests a stratigraphic sequence with interleaving clays and sulfates at the NH boundary. Similar stratigraphic sequences have also been observed in other areas of MP (Southern MP) by [5]. In the case of [5], a clay-bearing layer is overlain by other sulfates, generating a sulfate/clay/sulfate stratigraphic sequence. All this argues is in favor of several distinct climatic episodes pacing the NH climatic transition.
The results obtained so far will be enriched by further analysis of these areas along with a thorough investigation of the remaining 5 craters selected.
Acknowledgments: Featured CRISM data were downloaded from the Planetary Data System (PDS). This project is partially supported by Europlanet RI20-24 GMAP project.
References: [1] M. H. Carr and J. W. Head (2010) Earth and Planet. Sci. Lett., 293, 185-203. [2] B. L. Ehlmann and C. S. Edwards (2014) Annu. Rev. Earth Planet. Sci., 42, 291-315. [3] R. A. Craddock and A. D. Howard (2002) JGR, 107 (E11), 5111. [4] R. M. E. Williams et al. (2017) GRL, 44, 1669-1678. [5] J. Flahaut et al. (2015) Icarus, 248, 269-288. [6] B. M. Hynek et al. (2002) JGR, 107 (E10), 5088. [7] S. Murchie et al. (2007) JGR, 112 (E5), E05S03. [8] C. E. Viviano-Beck et al. (2015) MRO CRISM Type Spectra Library, NASA Planetary Data System. https://crismtypespectra.rsl.wustl.edu [9] J. P. Bibring et al. (2006) Science, 312, 400-404.
How to cite: Baschetti, B., Massironi, M., Carli, C., Altieri, F., and Frigeri, A.: Clay and sulfate-bearing terrains in Northern Meridiani Planum, Mars: constraining the characteristics of Mars’ early climate at the Noachian-Hesperian boundary, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-222, https://doi.org/10.5194/epsc2022-222, 2022.
1. Introduction
Plagioclase feldspar (Plg) is a common mineral in terrestrial rocks. It is a solid solution between a Ca-rich (anorthite) and a Na-rich (albite) endmember, and it is most commonly classified based on its anorthite (An) content. Powders of anorthite-rich Plg were previously studied using reflectance spectroscopy in the visible near-infrared (VNIR) range [1]. They showed that Plg display a band centered around 1.3µm due to Fe2+ substitutions, and that the position of this absorption band is a function of the An content.
Other studies have investigated mixture of binary powders and showed that the Plg spectral signature is no longer visible when 10%, or more, of mafic minerals are added [2, 3]. According to these studies, a minimum of 90% of Plg are necessary in the rock composition for its spectral signature to be visible on the average spectrum of the rock. A more recent study, mixing large Plg and pyroxene grains [4], showed that at least 50% of mafic minerals are needed to mask the Plg spectral signature.
Therefore, in addition to the An content, the size of the grains and the associated minerals influence the spectral signature of Plg. Thus, the analysis of whole rocks, and not powders, appears to be more relevant as a comparison with remote sensing analysis of planetary surfaces.
The present study seeks to understand when Plg signatures are detectable, and how the Plg absorption band is affected by the nature of the host rock. In other words, does the spectral signature of Plg differ from one rock type to another, and if so, can a reflectance spectrum in VNIR be associated with a specific feldspathic rock type?
2. Method
We combined petrological and spectral laboratory analyses of five terrestrial rock samples that contain Plg: an anorthosite (NM6), a granite (NJ11), two porphyritic basalts (NR1 and NR2) and a dacite (NJ2) (Figure 1).
Firstly, reflectance spectroscopy measurements were carried out on the macroscopic samples using an ASD Fieldspec 4 point-spectrometer. The instrument operates in three different wavelength ranges: VNIR (0.35 – 1 µm), SWIR 1 (1.001 – 1.801 µm), and SWIR 2 (1.801 – 2.5 µm), with a spectral resolution between 3 and 8 nm.
All resulting spectra (Figure 2) have an absorption band centered around 1.3µm with broad shoulders located around 0.8µm and 1.7µm. In order to accurately determine if this band is related to Plg in the rocks, additional analyses were performed.
A petrographic study of each sample mineralogy (Figure 1) was carried out using an optical microscope as shown for sample NR1 in Figure 3.
The use of hyperspectral cameras made it possible to further determine the spectral signature of each grain contained in these rocks (Figure 1). Hyperspectral cubes were acquired with the HySpex VNIR-3000-N and SWIR-640 cameras that acquire high-resolution data respectively from 0.4µm to 1µm, and from 0.96µm to 2.5µm, at a distance of 30cm from the sample. The resulting pixel size is about 29 µm in the VNIR, and 130 µm in the SWIR. The hyperspectral cubes are converted to reflectance using a reference target, and then analyzed with the ENVI software to classify the image pixels according to their spectral signature. Therefore, the different minerals in the rocks, which are often on a millimeter scale, are grouped into different classes. The statistics give the mean spectrum of each class, and therefore each mineral group (Figure 4).
3. Results and Discussion
For each sample, the mineralogical composition (Figure 3) and spectral signature of each mineral (Figure 4) are determined. We observe that only Plg has an absorption band centered at 1.3µm with broad shoulders at 0.8 and 1.7µm. In conclusion, this same absorption band, that we see on the average spectrum of the rock (Figure 2), is the spectral signature of Plg. However, it should also be noted that in the matrix of Figure 4, composed of Plg and iddingsitized olivine, this band is no longer visible. This is also the case for the other samples: some minerals can mask the spectral signature of Plg by overlaying or attenuating its absorption band.
Looking at the reflectance spectra (Figure 2), the position of the band seems to vary. It is centered around 1.2µm for dacite (NJ2) and granite (NJ11), around 1.25µm for basalts (NR1 and NR2), and 1.3µm for anorthosite (NM6). However, one must be careful with the interpretation: this shape might be related to the Plg chemical composition, but also the grain size, and the presence of other minerals contributing to the average rock spectra.
Our study, therefore, shows that it is indeed possible to detect the presence of Plg in a whole feldspathic rock, even though it does not contain 90% of feldspar, and regardless of its nature (e.g., sample NR1 shown in Figure 4 contains ~66% of Plg).
These results can be applied to the study of feldspathic rocks at the surface of rocky planets and more precisely of Mars. Indeed, recent detections of Plg [5, 6, 7] were made using the CRISM instrument (MRO) at the surface of Mars. The interpretation of these signatures, in terms of lithologies, is still under discussion given the variety of feldspathic rocks containing plagioclase [4, 5, 6, 7, 8] that exhibit the typical Plg absorption band. The construction of a reference library acquired on macroscopic rock fragments that we undertook should lead to a more accurate interpretation of Martian detections.
4. References
[1] J.B. Adams an L.H. Goullaud (1978). LPSC Conference, 9th, 3, 2901-2909 (A79-39253 16-91).
[2] D.A. Crown and C.M Pieter (1987). Icarus, 72(3), 492-506.
[3] L.C. Cheek et al. (2014). American Mineralogist, 99(10), 1871-1892.
[4] A.D. Rogers et H. Nekvasil (2015). Geophy.Res.Lett., 42, 2619-2626.
[5] J.J. Wray et al. (2013). Nature Geoscience, 6, 1013-1017.
[6] J. Carter et Poulet (2013). Nature Geoscience, 6, 1008–1012.
[7] J. Flahaut et al. (2020). EGU General Assembly (EGU2020-13377).
[8] A.D. Rogers et W.H. Farrand (2022). Icarus, 376, 114883.
How to cite: Barthez, M., Flahaut, J., Guitreau, M., Pik, R., and Ito, G.: Reflectance spectroscopy and optical microscopy laboratory analyses of terrestrial feldspathic rocks as analogs to Mars, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-467, https://doi.org/10.5194/epsc2022-467, 2022.
Introduction.
Earth's most-ancient crust has been recycled through plate tectonics processes making it unlikely that we will ever directly sample it (although, one can imagine finding ancient Earth meteorites one the Moon [1].) Mars, on the other hand, hosts ancient crustal outcrops on its surface. The uplifted massifs surrounding Argyre, Hellas, and Isidis – the three largest, well-preserved impact basins on Mars - formed in the chaotic aftermath of the basin-forming impacts due to normal faulting caused by crustal thinning from impact excavation [2]. Our goal is to understand the igneous minerals associated with uplifted massifs using the Compact Reconnaissance Imagining Spectrometer for Mars (CRISM) [3] around Argyre, Hellas, and Isidis (Fig. 1). Here, we present initial results in this effort for the north Hellas area and expect to present preliminary results for Argyre and Isidis, as well, at the conference.
Fig. 1 Context view of the study area. Squares outline 5°x5° CRISM tiles. Number of tiles is 100, covering an approximate 5% of the surface. CRISM coverage is >80 % over tiled areas. Inset shows a region at the map scale of 1:250,000 with CRISM spectra of uplifted massifs compared to library spectra. In the spectral parameter combination, red is consistent with olivine, yellow with plagioclase, and blue with low-calcium pyroxene.
Methods.
CRISM Data Processing. We used CRISM multispectral mapping data (MSP) and hyperspectral mapping data (HSP). The MSP mapping strips have 19 visible to near-infrared (VNIR, 0.4-1 µm) spectral channels and 55 short-wavelength infrared (SWIR, 1-4 µm) channels, and the HSP mapping strips contain 107 VNIR channels and 154 SWIR channels. Both mapping datasets have a ground sampling distance of approximately 180 m. The set of wavelength channels contained in the MSP dataset were chosen to sample more densely in wavelengths regions known to contain absorption features of minerals likely to be detected on Mars (primary rock-forming silicates, phyllosilicates, etc. [3]). For our study, HSP data were resampled to the MSP wavetable to increase the spatial coverage. Typical coverage of the MSP+HSP dataset is ~85%, with sufficient overlap to allow for mosaicking and radiometric reconciliation. We processed these data through a custom pipeline [4] that includes initial noise filtering, photometric and atmospheric corrections [5], [6], and an empirical correction for “spectral smile” [7]. The final products of this pipeline are 5°x5° mosaic tiles with improved inter-strip variability in atmospheric residuals [8].
A typical method for condensing the information contained in a CRISM image into an interpretable form is by calculating “spectral parameters”, i.e., mathematical summations of particular characteristics of the spectra [9]. Spectral parameters can be combined into 3-band RGB images that highlight specific, thematically-related, combinations of interest. Fore example, the MAF summary product combines indexes intended to highlight mafic mineralogy: olivine (OLINDEX3), low-calcium pyroxene (LCPINDEX2), and high-calcium pyroxene (HCPINDEX2). From the CRISM mapping tiles, we constructed summary products that are well-suited for compositional mapping over large areas [10] (e.g., Fig. 1).
Compositional Mapping. Regions of interest were identified with the map tile summary products in ArcGIS followed up by detailed spectral analyses in IDL/ENVI (specialized software for analyzing hyperspectral images) with custom add-on analysis tools. Point locations of compositions, confirmed through spectral analysis, were imported back into ArcGIS and “outcrops” were mapped using summary products. We define outcrop in the context of this work as a spatially contiguous region with an internally consistent spectral signature distinct from its surroundings (e.g., Fig. 2).
Fig. 2 Example plagioclase-bearing massif north of Hellas basin. (A) CRISM browse product (same as in Fig. 1). Yellow tones are consistent with plagioclase. Black boxes indicate 8 regions over which spectra were taken and plotted in C. (B) CTX 5 m/pixel image of the same massif as in (A). White dashed lines denote outcrops mapped in this A and B. (C) Average CRISM ratioed I/F spectra from the 8 regions indicated in A and B.
Results and Discussion.
Thus far, we have mapped 12 high-calcium pyroxene-bearing outcrops, 97 plagioclase-bearing outcrops, 128 LCP-bearing outcrops, and 129 olivine-bearing outcrops (Fig. 3). Outcrops with distinct mineralogical signatures are often observed adjacent to each other on the same massif, or on massifs in close spatial proximity (relative to the size of the massifs, ~several kilometers). We also identified Fe-, Mg-, and Al-phyllosilicate minerals associated with the massifs and, more commonly, with impact crater ejecta along the northern Hellas rim.
The number and spatial extent of plagioclase-bearing outcrops was surprising and is described in [11]. The massifs pre-date Hellas (≥ 4.1 Ga) and are situated stratigraphically above putative mantle material. The north Hellas massif outcrops may expose the remains of an ancient large igneous complex, perhaps similar to terrestrial layered mafic intrusions. Preliminary results from the Argyre and Isidis uplifted massifs will be presented at the conference and compared to those from north Hellas.
Fig. 3 Summary of detections over north Hellas. (A) Red squares indicate all locations of plagioclase-rich outcrops discovered previous to our work. (B) Context map showing all mafic mineral outcrops mapped in our study. Arcs are 50-km interval bins measured radially from the center of Hellas. Geologic units are Noachian crater (Nc), Noachian highland (Nh) and Noachian massif (Nm) from Leonard and Tanaka, 2001. (C) %Area is the area of each mineral outcrop normalized to the area of the Nc, Nh, and Nm geologic units in each radial bin. Note the concentration of detections interior to the nominal radius of Hellas, highlighting the stratigraphically low position of the outcrops.
[1] J. J. Bellucci et al. doi: 10.1016/j.epsl.2019.01.010.
[3] G. J. Leonard and K. L. Tanaka, 2001.
[4] S. L. Murchie et al. doi: 10.1029/2009je003344.
[5] F. P. Seelos and S. L. Murchie, LPSC. p. 2325, 2018.
[6] F. P. Seelos, et al., LPSC. p. 1783, 2016.
[7] F. Morgan et al., LPSC. p. 2453, 2011.
[8] F. P. Seelos et al., LPSC. p. 1438, 2011.
[9] F. P. Seelos, et al., LPSC p. 2635, 2019.
[10] C. E. Viviano‐Beck et al. doi: 10.1002/2014JE004627.
[11] C. E. Viviano et al., LPSC, p. 1485, 2020.
[12] Phillips, M. S., et al., Geology, accepted.
How to cite: Phillips, M., Viviano, C., Moersch, J., Rogers, A. D., and Seelos, F.: Mars uplifted massifs: unique and extensive samples of ancient crust., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-736, https://doi.org/10.5194/epsc2022-736, 2022.
TP5 | Mars Science and Exploration
Introducction
JAXA’s MMX (Martian Moons eXploration) mission, to be launched in 2024, will study both Martian satellites, for several years, and will drop a small rover to Phobos, to explore its surface [1]. As part of this rover scientific payload, it will be placed a Raman spectrometer, the RAX Instrument (Raman Spectrometer for MMX). The RAX will be able to analyse the mineral composition of the Phobos regolithe surface with in-situ measurements, complementing the Japanese Sample Return mission, and helping to reveal the nature and distribution of materials on the Martian Moon’s surface, and ultimately its origin and evolution [2].
The RAX instrument [3] has been designed, manufactured, integrated and tested by an international consortium led by DLR (Germany), with significant contributions from JAXA & University of Tokyo (Japan), and INTA-CAB-UVa (Spain). One of the Spanish contributions to RAX, will be the instrument Verification Target, a small piece of PET (polyethylene terephthalate) attached to MMX spacecraft, to be used before launch, and during cruise; for spectral instrument performances verification on-ground and just before the rover release to Phobos.
Figure 1. RAX Verification Target design proposed by INTA-CAB-UVa
Experimental
Thanks to previous expertise of the UVa-INTA group with PET material, used on the Raman Laser Spectrometer (RLS) Calibration Target [4] for ESA’s ExoMars mission; and SuperCam Calibration Target [5] for NASA Mars2020; a newly design-deuterated PET material, decreasing the PET fluorescence background, and adding new Raman bands with respect to ordinary PET [6] has been developed, manufactured, characterized and space-qualified for MMX-RAX mission by INTA-CAB-UVa; so it was proposed as candidate the RAX Verification Target.
Figure 2. RAX Verification Target Flight batch for qualification/acceptance
Results and discussion
During the session, a detailed description of different tests carried out for the space qualification of the deuterated material, will be shown. And how the final performances with respect to other commercial PETs have been improved; and so, how the final verification-calibration of the Raman instrument has been optimized.
Acknowledgements
INTA’s internal I+D+I project IDMats; and MICINN grants PID2019-107442RB-C32 & PID2019-107442RB-C31
References
[1] Michel P. et al. (2022) Earth, Planets and Space 74, 2.
[2] Hagelschuer, T. et al. (2019) 70th Int. Astronautical Congress, 2019.
[3] Hagelschuer, T. et al. (2022) 73th Int. Astronautical Congress.
[4] López-Reyes, G. et al. (2020) Journal of Raman Spectroscopy, 1-13
[5] Manrique, J.A. et al. (2020) Space Sci Rev, 216:138
[6] Mora, J. et al (2020) Acta Astronaut. 167 (2020) 360–373
How to cite: Moral, A. G., Mora, J., Prieto-Ballesteros, O., Fernández Sanpedro, M., López-Reyes, G., Ercilla, O., Sanz Arranz, J. A., Herrera, A., Pérez, C., Rull, F., Böttger, U., Cho, Y., Schöder, S., and Hübers, H.-W.: Improving the Polyethylene Terephtalate (PET) perfomances, for the RAX Verification Target for MMX mission, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-784, https://doi.org/10.5194/epsc2022-784, 2022.
Introduction
The detection of anomalous bright reflections beneath the Martian SPLD by MARSIS radar has sparked a vast debate on the characterization of the basal material. The source of the reflections has been interpreted by someone as an evidence of basal liquid salty water [1, 2], while by others as clay sediments or volcanic rocks [3, 4]. Though it has been demonstrated that clays cannot be the responsible of the strong reflections [5], it has not yet been well understood if the dielectric permittivity of the volcanic rocks can be so high as to cause the reflectivity seen by MARSIS. Furthermore, although there are in literature several attempts to demonstrate a correlation between the dielectric properties of volcanic rocks and their whole-rock compositions [6], these data can hardly be compared with each other, since every work employs different experimental setup and procedures. Therefore, a definitive dataset of the permittivity of such samples and planetary simulants does not yet exist, especially at the operating frequencies of planetary radar sounders ( 1 MHz - 1 GHz). The present work aims to be a first step towards a reliable dataset of electromagnetic measurements of volcanic rocks, investigating the relation between their geochemical and their electric and magnetic properties.
Methodology
Sample characterization
We studied the granular samples of three different volcanic rocks that are plausibly representative of the overall surface compositions of the terrestrial planets [7]. In the following, the samples are named as: St. Augustine (2006), Etna (1991-1993) and Etna (Holocene). The St. Augustine (2006) sample is a lava rock coming from the 2006 eruption of the St. Augustine stratovolcano in Alaska [8]. Sample Etna (1991-1993) comes from the Piana del Trifoglietto lava field at SE of Etna summit craters generated by the eruption started on December 1991 and stopped on March 1993 [9]; the rock is characterized by a potassic geochemical signature. Sample Etna (Holocene) is a mugearite from Pizzi Deneri Formation and it comes from an ancient eruption (57000-15000 years ago), representing the more sodic volcanic activity [10]. In Fig. 1 and Tab. 1 are shown respectively the TAS diagram of the samples and their geochemical composition.
The samples exhibit different grain densities: ρSt. Augustine(2006) = (2.736± 0.001) g/cm3, ρEtna(91-93)= (2.961 ± 0.001) g/cm3 and ρEtna(Holocene)= (2.787 ± 0.001) g/cm3.
Table 1. Whole-rock compositions of the samples.
Figure 1. Total Alkali vs. Silica diagram of the samples.
Electromagnetic measurements and mixing formulas
The electromagnetic measurements were carried out with a two port Vector Network Analyzer (VNA), employing a cage coaxial cell and using the experimental procedure and setup described in [11]. The complex permittivity ε and magnetic permeability µ were estimated by using the Nicholson-Ross-Weir algorithm and the equations slightly modified in [12]:
where Fg is a factor related to the geometry of the cell, Γ and Ψ are the reflection and transmission coefficients, le = 5 cm is the electrical length of the cell, c is the velocity of the light in a vacuum and ν is the frequency. The complex effective permittivity of the two phases granular rock-air was studied using Lichtenecker and Bruggeman mixing formulas:
where εi and εeare respectively the permittivity of the environment (the solid grains) and inclusions (air) and f = 1- Φ is the volume fraction of the grainsin the sample, with Φ the porosity.
Results and conclusions
Measurements with the VNA were performed on the granular samples at room temperature, for percentage porosities ranging from 31% to 55%. The magnetic permeability µ is not reported because the three samples do not show a magnetic behavior (and then we can consider µ ≃ 1). Fig. 2 illustrates the complex dielectric permittivity as a function of frequency and at Φ = 0.36. Gray areas in the plots show values that are not reliable since at high frequencies the NRW algorithm diverges because of the cell resonances. Data have larger uncertainties at low frequencies due to VNA instrumental limits. The two Etna samples show a similar dielectric behavior, instead the St. Augustine sample has lower values of both real and imaginary part of permittivity. In the end, we fitted at 80 MHz the complex permittivity as a function of porosity using eqs. 3 and 4. In Tab. 1 we show the measurements at Φ = 0.36 and the values obtained with the mixing formulas at Φ = 0. The St. Augustine sample has the lower values of the solid complex permittivity, probably due to its lower iron abundances and higher abundances of SiO2, while the two Etna samples show a similar dielectric behavior. Further measurements will be required in the future in order to identify the relation between the electromagnetic properties and the geochemical compositions of volcanic rocks that can be accounted as good simulants of the surface and subsurface of terrestrial planets, such as Mars and Venus.
Figure 2. Complex permittivity frequency spectra of the samples.
Table 2. Complex permittivity measured at Φ = 0.36 and fitted at Φ = 0 with eqs. 3 and 4.
References
- Orosei R. et al. (2018) Science, 361(6401), 490-493
- Lauro S. E. et al. (2020) Nat. Astron., 5(1), 63-70
- Smith I. B. et al. (2021) Geophys. Res. Lett. 48, 15
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How to cite: Brin, A., Salari, G., Lauro, S. E., Cosciotti, B., Mattei, E., and Pettinelli, E.: Electromagnetic and geochemical characterization of volcanic rock samples in the framework of radar exploration of terrestrial planets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-956, https://doi.org/10.5194/epsc2022-956, 2022.
TP6 | Martian dust and clouds: from lab to space
TP12 | Planetary Seismology and Geophysics
The Apollo Passive Seismic Experiments recorded more than 13000 events on the Moon during 1969-1977 [1]. However, not all of these events were used in our previous studies on the Moon due to the degradation of the quality of the recorded data (Figure 1A). To make better use of Apollo seismic data, we propose several new methods to reprocess it. First, since Apollo seismic records sometimes contain invalid data in every station and component (including the short period component), we removed these invalid data from raw Apollo records using time and ground station number. Then we removed several special spikes with the help of amplitude histogram. This enables us to compute the envelopes for a larger number of moonquake events. Acceleration and displacement step responses are used to fit glitches using the Lagrange multiplier method. The ‘glitches’ we term here are artifact one-sided pulses in the raw data. We find that the instrument response parameters vary with time. So, we determined the instrument response parameters with the calibration signal and removed it near the event. Finally, we used the smoothed envelope to detect the single spike (spike with only one point) and removed it when exceeds the envelope. These new processing steps lead to considerably cleaner Apollo data (Figure 1B), yield a more accurate arrival time reading, and result in an envelope that reflects more realistic waveform characteristics. We expect that additional moonquake records will become available with these methods for future research. Further study of the instrument response variations of the Apollo seismometer will also provide a reference for the new lunar seismometers to be deployed in upcoming space missions.
Figure 1. An example of a comparison plot before (A) and after (B) Apollo moonquake data processing.
Reference:
[1] Nunn, C., Garcia, R. F., Nakamura, Y., Marusiak, A. G., Kawamura, T., Sun, D., et al. (2020), Lunar seismology: A data and instrumentation review. Space Science Reviews, 216(5), 89. doi:10.1007/s11214-020-00709-3
How to cite: Zhang, X., Lognonné, P., Kawamura, T., Samuel, H., Xu, Z., Sainton, G., Froment, M., and Onodera, K.: Reprocessing Apollo seismic data, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-846, https://doi.org/10.5194/epsc2022-846, 2022.
TP13 | Planetary Dynamics: Shape, Gravity, Orbit, Tides, and Rotation from Observations and Models
Introduction
Most spacecraft missions to small bodies provide the gravity field of their targets. As the extended gravity field is an expression of the mass distribution within the body, it can provide information about its interior structure, and that in turn can constrain its origin and history.
We present a method to detect density anomalies within a small body from the global gravitational potential. As is well known, such an inverse problem is ill-posed [1], and requires regularization. Our main assumption, which mitigates the non-uniqueness of the problem, is that the interior of the body is composed of a finite number of domains, in which the density is uniform. The boundary of each domain is therefore a surface, that we describe as the level-set of a function. This approach, known as the level-set method, has been extensively used in local inversions of Earth’s gravity measurements [2]. It simplifies the manipulation of complex shapes, which in our case delimit the density anomalies.
In order to reduce the dimensionality of the problem, we employ parametric expressions for the level-set functions. The aim is then to determine the parameters of each level-set function, which describe the location and size of the anomalies, along with the density within each anomaly and the bulk density of the body.
Methods
We model the gravity field of the body through a mascons approach [3]. The observables we consider are the coefficients of the spherical harmonic expansion of the potential. By implementing a continuous approximation for the unit step function, the partials derivatives of the measurements with respect to the level-set function parameters can be computed via the chain rule [4]. Then, the function parameters and the densities can be estimated via non-linear least-squares inversion of the gravity data.
However, the problem is generally non-convex, which means that in order to converge to a global optimum the a priori values for the unknowns should be close to this solution. Since we assume no initial knowledge of the distribution to retrieve, a preliminary step is needed for the definition of an a priori model. To this end, we generate a Voronoi partition of the interior from randomly sampled points within the body. The domains are now fixed, and only the densities within each Voronoi cell are estimated from the data. This inversion problem is linear, but the solution will depend on the partition of the body. However, averaging solutions from many of such random partitions can provide a good approximation of the true model [5]. This averaged solution is then used to initialize the values of the level-set algorithm.
Discussion and outlook
We have tested the ability of our level-set implementation to retrieve interior models from simulated gravity data.
Figure 1 shows an example of the inversion results for a Bennu-shaped body. In this case, the level-set functions are chosen so that the anomalies they describe are cuboids. The model in Figure 1a is the ground truth, used to simulate gravity coefficients up to degree 11. Figure 1b shows the density retrieved from the noise-free data, and Figure 1c the results when the data are perturbed by 1% Gaussian noise. The method can retrieve the location and density of the anomalies with good approximation, even in the perturbed case. For anomalies where the density and the size cannot be estimated simultaneously, such as with nearly-spherical shapes, the method can usually still correctly determine the total mass and the position of the center-of-mass. The size could then be constrained by independent observations from other instruments or by theoretical models.
In a more realistic scenario, the resolution of the gravity would be lower, and the noise profile would be increasing with the degree of gravity. This could aggravate the non-uniqueness problem, since having fewer and less precise measurements could lead to different models fitting the data equally well. Current work is focused on improving the robustness of our approach and on better defining its limitations in its application to real gravity measurements.
Figure 1. Interior density models, shown via sections along 3 planes perpendicular to the body axes and containing the origin: a) Ground truth; b) Solution from noise-free data; c) Solution from data with 1% noise
Acknowledgements
This work was financially supported by the French community of Belgium within the framework of a FRIA grant, and by the Belgian PRODEX program, managed by the European Space Agency in collaboration with the Belgian Federal Science Policy Office.
References
[1] V. Isakov. Inverse Source Problems. American Mathematical Soc., 1990.
[2] J. Giraud, M. Lindsay, and M. Jessell. Generalization of level-set inversion to an arbitrary number of geologic units in a regularized least-squares framework. GEOPHYSICS, 86(4):R623–R637, July 2021.
[3] S. Le Maistre, A. Rivoldini, and P. Rosenblatt. Signature of Phobos’ interior structure in its gravity field and libration. Icarus, 321:272–290, March 2019.
[4] A. Aghasi, M. Kilmer, and E. L. Miller. Parametric Level Set Methods for Inverse Problems. SIAM Journal on Imaging Sciences, 4(2):618–650, January 2011.
[5] L.-I. Sorsa, M. Takala, P. Bambach, et al. Tomographic inversion of gravity gradient field for a synthetic Itokawa model. Icarus, 336:113425, January 2020.
How to cite: Caldiero, A., Le Maistre, S., and Dehant, V.: A parametric level-set approach to the global gravity inversion of small bodies, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1118, https://doi.org/10.5194/epsc2022-1118, 2022.
TP14 | Impact Processes in the Solar System
Introduction: The dating of geological surfaces on the Moon is crucial for understanding its geological history and evolution. The measurement of Crater Size-Frequency Distributions (CSFDs) can be used for determining relative and absolute ages of surfaces. Older surfaces reflect more and larger craters than younger geological units [1-4]. To determine the relative surface ages, a production function (PF) is constructed to which the CSFD is fitted. One frequently used PF was empirically-derived by measuring craters on reference surfaces using Apollo era data (Neukum, 1983 [1]), which was revised in 2001 [5], and is valid for crater diameters of 10 m - 300 km and 10 m - 100 km, respectively. With increased image resolution of more recent missions [e.g., 6], it has been possible to measure CSFDs for crater diameters down to a few meters. Therefore, it would be beneficial to be able to extend the PF to smaller crater diameters, which would allow the determination of relative and absolute ages for young/small geological units.
A crucial influence on small craters formed in the strength regime are target properties, which has been investigated in several studies [e.g., 7, 8, 9]. Therefore, we aim to perform the crater counts exclusively on continuous ejecta blankets. Secondary craters [e.g., 10-12] influence the CSFD as well and can contaminate the count area, causing a steeper CSFD-slope [e.g., 10, 13, 14]. To avoid this effect and obtain the cleanest PF possible, we selected ejecta areas derived from young Copernican-aged craters. This minimizes the number of field secondary craters on the ejecta and also avoides major degradation of the small craters [15, 16]. However, the identification of self-secondary craters remains problematic, since they occur irregularly distributed on the ejecta blankets and often have morphologies similar to primary craters [e.g., 12, 13].
Method: We used Lunar Reconnaissance Orbiter Narrow Angle Camera (NAC) images [6] including M180509194LE, M1122929850LE and M103831840LE/RE at Giordano Bruno (GB), M1107052575RE and M1112971104RE at Moore F, M129187331LE/RE at North Ray (NR), M119754107RE at South Ray (SR) and M114064206LE at Cone. The resolutions vary between 1.6 m/px and 0.5 m/px, the incidence angles are from 54° to 78°. The CSFDs were measured in ArcGIS with the CraterTools add-in of [18] and displayed in CraterStats with pseudo-log binning [19].
Two areas were investigated at Cone, three at GB, Moore F and SR, respectively. Four areas were investigated by [17] at NR. The selected counting areas are all on the ejecta blakets of the named craters.
Results: Similar to [17] we combined the statistics from the separate count areas into one file and display these CSFDs in a cumulative plot in Figure 1.
Figure 1: Display of the combined CSFDs at GB (green), Moore F (blue), NR (violet), SR (red) and Cone (orange), respectively. The vertical lines of individual data points represent the error bars.
The comparison between the individual CSFD-slopes at GB, Moore F, NR, SR and Cone generally show slightly steeper slopes than the nominal -3 slope of [1] for crater diameters between 10 m and 23 m (in our case 20 m, see Table 1).
Table 1: Display of the considered crater diameter range and the respective CSFD-slopes.
Discussion: We found that the CSFD-slopes on the ejecta blakets of the investigated craters show a tendency regarding the crater diameter. Considering only diameters ≤10 m the slope is marginally shallower than Neukum’s [1] -3 slope, except at GB, which might be explained through secondary cratering. This trend was also observed by [15] (and references therein) and [20] who investigated NR, Cone, Copernicus and Tycho. This might suggest that CSFDs of young Copernican craters have actually a slightly shallower slope at smaller crater diameters. Another possible explanation is the faster degradation of smaller craters [e.g., 21]. Further effects might be the coverage of ejecta material of nearby craters; NR (52.3 Ma [20]), might be influenced by the ejecta of SR (2 Ma [22]), SR by Baby Ray. Moreover, larger craters in two areas at NR and Cone probably penetrated through the ejecta blanket, which can lead to mixed target propertie effects.
Further investigations are required to quantify the effects of secondary cratering, target properties, crater degradation or impactor flux on the determination of our CSFDs. Additional investigation is necessary to determine at which crater diameter the slope becomes shallower or if a transition zone is present.
Acknowledgments: This Project is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 263649064 – TRR 170.
References: [1] Neukum (1983), NASA TM-77558. [2] Öpik (1960), RAS 120(5), 404-41. [3] Shoemaker et al. (1970), Science, 167 (3918), 452-455. [4] Baldwin (1971), Icarus, 14, 36-52. [5] Neukum et al. (2001), Space Sci. Rev., 96, 55. [6] Robinson et al. (2010), Space Sci. Rev. 150, 81-124. [7] van der Bogert et al. (2010), LPSC 41, #2165. [8] Wünnemann et al. (2011), Proceedings of the 11th hypervelocity impact symposium., Vol. 20. [9] van der Bogert et al. (2017), Icarus, 298, 49-63. [10] McEwen and Bierhaus (2006), Annu. Rev. Earth Planet. Sci. 34, 535-567. [11] Xiao and Strom (2012), Icarus 220, 254. [12] Zanetti et al. (2017), Icarus 298, 64-77. [13] Plescia et al. (2010), LPSC 41, #2038. [14] Plescia and Robinson (2011), LPSC 42, #1839. [15] Moore et al. (1980), Moon and Planets, 23, 231-252. [16] Fassett and Thomson. Journal of Geophysical Research: Planets 119.10, 2255-2271. [17] Hiesinger et al. (2012), JGR 117, E00H10. [18] Kneissl et al. (2011), PSS 59, 1243-1254. [19] Michael et al. (2016), Icarus 277, 279-285. [20] Williams et al. (2014), Icarus 235, 23-36. [21] Mahanti et al. (2018), Icarus, 299, 475-501. [22] Stöffler and Ryder (2001), Space Sci. Rev., 96, 9-54.
How to cite: Oetting, A., Hiesinger, H., and van der Bogert, C.: Refinement of the Lunar Production Function - The CSFD-Slope of Small Crater Diameters on Ejecta Blankets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-828, https://doi.org/10.5194/epsc2022-828, 2022.
1. Introduction
Asteroid impacts, ranging from small-scale cratering events to catastrophic disruption, have played a crucial role in the formation and evolution of asteroids (Jutzi et al., 2015). Thanks to the increasing performance of computers, shock-physics numerical codes have become commonly used in the field of hypervelocity impacts, to extrapolate experimental results and help us be better prepared for space missions devoted to asteroid deflection using the kinetic impactor techniques, such as the NASA DART (Rivkin et al. 2020) and ESA Hera missions (Michel et al. 2022), and evaluate the outcomes.
Past numerical studies showed us that it is possible to divide the asteroid impact process into two stages that occur at very different time scales, the early stage of fragmentation of the asteroid and the late stage of gravitational reaccumulation of the fragments (e.g, Michel et al. 2001). For the early stage, various numerical methods have been developed to solve this short but extreme physical process, such as the Smooth Particle Hydrodynamics (SPH) technique used in codes like the Bern SPH and grid techniques used in codes like CTH or iSALE. Each method has its unique advantages, but they share a common challenge that the contact and the boundary condition are not well handled (El Mir et al., 2019).
In this study, we exploit the Material Point Method (MPM) framework, an extension of the particle-in-cell method, to simulate the early stage of impact in order to offer a new approach and solutions to the above problems.
2. Methods
MPM is a meshfree method, characterizing the material domain by a group of points. These Lagrangian material points carry all state variables. Meanwhile, a predefined regular background grid is used. In each timestep, material information is mapped to grid nodes, to solve the momentum equations, and material points deform with the grid. Then the information is mapped back to the points to update their positions and velocities, discard the deformed grid, and reset a new one to calculate the next timestep (Zhang et al., 2013). MPM framework combines the advantage of both Lagrangian description and Eulerian description, which not only avoids the undesirable mesh tangling caused by large deformations, but also eliminates the difficulties in solving contact and boundary conditions.
As such, MPM is well used in simulating impacts, explosions, and metal forming of on-earth situation (Zhang et al., 2013). So far, it has not been commonly used to model hypervelocity impacts on asteroids (El Mir et al., 2019). Hence, we start with building material models that are applicable to asteroids made of porous and brittle materials.
The material models include Drucker-Prager strength model that describes cohesion and pressure-dependent strength effect. We also use the Tillotson equation of state for basalt coupled with the P-alpha model which accounts for porosity, and as stress-based failure criterion consistent with Weibull distribution. The framework is thus similar to that used by other studies using the SPH numerical method (Raducan and Jutzi, 2021). Our MPM model is then validated by comparing with laboratory impact experiments and the simulations using the SPH method.
3. Results
We compare our simulations with SPH simulations (Benz & Asphaug, 1994) and the impact experiments (Nakamura et al., 1991) on non-porous basalt sphere used to validate them. Our result shows that our material model under the MPM framework can successfully characterize the shell-like propagation of the failure zone (Fig 2.c2). However, a concentration of stresses reflected back from the boundary subsequently occurres, resulting in a severe secondary failure in the nuclear region. (Fig 2.c3) This stress concentration may cause by the unsmooth discrete boundary and the lack of energy dissipation. The analysis of large fragments reveals this problem too: although with a similar mass distribution, the velocity of the largest fragment in MPM simulation is significantly higher (Fig 3.a). Apart from that, the simulation results are otherwise in good agreement with the previous studies, especially the shape of the largest fragment of MPM simulation (Fig 3.b) versus a recent experiment (Fig 3.c). Noting the usual spreading in experimental outcomes using same conditions, the MPM method can thus be considered valid.
Further research will be centered on verifying the P-alpha model and the correct treatment of porosity (Jutzi et al., 2009).
4. Conclusion and Discussion
The MPM framework can complement of other shock-physics code to balance the accuracy and efficiency of calculation. Furthermore, the mentioned features of solving contact and boundary conditions with MPM broadens the application of the simulation algorithm in the hypervelocity impact stage, and may make it easier than SPH models to combine with the Soft-Sphere Discrete Element Method (SSDEM) code (Fig 4) to simulate the two-stage impact process (SPH-SSDEM method refers Zhang et al., 2021).
All these studies will offer a glimpse into the active processes from the early formation of the solar system to the current epoch, and contribute to planetary defense.
Acknowledgements:
We acknowledge support from the Université Côte d’Azur. X.Y. acknowledges support from Tsinghua University, funding from the Chinese Scholarship Council, and the National Natural Science Foundation of China (No. 11872223). P.M. acknowledges funding from CNES, from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 870377 (project NEO-MAPP) and from the CNRS through the MITI interdisciplinary programs.
References:
Arakawa, M. et al. (2020) Science, 368, 67–71.
Arakawa, M. et al. (2022) Icarus, 373, 114777.
Benz, W., & Asphaug, E. (1994) Icarus, 107(1), 98–116.
El Mir, C. et al. (2019) Icarus, 321, 1013–1025.
Raducan, S.D. & Jutzi, M. (2021) 52nd LPSC, #1900.
Jutzi, M. et al. (2009) Icarus, 201(2), 802–813.
Jutzi, M. et al. (2015) In: Asteroids IV (Michel P. et al., eds.) 679–699.
Michel et al. (2001) Science, 294, 1696-1700.
Michel et al. (2022) Planetary Science Journal, accepted.
Nakamura, A., & Fujiwara, A. (1991). Icarus, 92, 132–146.
Rivkin, A. et al. (2020) Planetary Science Journal, 2, 173.
Zhang, X. et al. (2013) Beijing: Tsinghua University Press.
Zhang, Y. et al. (2021) 52nd LPSC, #1974.
How to cite: Yan, X., Liu, Y., Zhang, Y., Michel, P., and Li, J.: Hypervelocity impact simulation on asteroids with MPM framework, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1064, https://doi.org/10.5194/epsc2022-1064, 2022.
Introduction
A lunar impact flash (LIF) is a rapid burst of light caused by a hypervelocity impactor hitting the moon, releasing a fraction of its energy as light. They are observable though moderately sized (0.4m) telescopes, and are therefore observable by both amateur and professional astronomers.
LIF observations are typically performed in visible or NIR, and can only take place when the lunar phase is between 10-50%, during local night, and are only observable against the lunar night-side; the most commonly observed LIFs are faint, approximately MagI = 9, MagR = 10 [1], making them indistinguishable against the illuminated lunar background. This limits potential observations of LIFs to ~30h per month on average, with weather limiting this further.
In order to increase the average number of observable hours that LIF observations can be made, and thereby increase the number of observed LIFs, we have developed new techniques to perform LIF observations at all local times, and all lunar illuminations. This technique theoretically only requires clear weather and a visible moon.
Theory
LIFs have been shown to behave as black bodies, releasing energy according to Planck's law [2]. The temperature of LIFs observed by NELIOTA is between 1300-5800 k, with average temperature, Tavg = 2800k [3]. This average has peak wavelength of λpeak = 1.035 μm. The illuminated portion of the lunar surface is reflecting light from the sun (T = 5778 k, λpeak = 0.5 μm). In R-band and I-band, the ratio of energy radiated by the sun is greater by a factor of 57 in R-band, and 28 in I-band. My observing in wavelengths closer to the λpeak of the flash, we can improve this ratio greatly.
Figure 1:The Planck curve for the sun (5778k) and the average LIF (2750k), R, I, and J-band regions are highlighted in orange, red, and grey respectively.
As illustrated in Fig. 1, by observing in J-band the irradiance of the sun is lowered, being only 10 times greater than the 2800 k LIF. This effective dimming of the background leads to an increase in the signal-to-noise ratio (S/N) of the LIF against the sun-illuminated background.
The S/N ratio is a measure of how detectable a signal is above the background, and can be defined as:
S/N = S" / (σ × √Apix)
Where S" is the total count of the signal, σB is the standard deviation of the background, and Apix is the area of the background measurement. A S/N ratio above ≈10 is generally required for a signal to be considered detectable.
Observations
Observations were performed on 2022-02-23 from the Observatoire de la Côte d'Azur, using a 0.5 m diameter, 2 m focal length telescope with Ninox 640 II camera and J-band filter attached. For the first set of observations, high gain mode was used, for the second set of observations low gain mode was used. A 30 μm exposure time was used for both sets of observations.
The star HD137463 was observed, which has MagJ = 5.423, obtained by Simbad [4] Observations began during the night, and continued until after sunrise in order to measure the brightness of the sky during daytime.
By performing A-B subtraction to remove the dark current and background of the observed frames, as shown in Fig. 2, a pixel count for the clean star signal, S", can be obtained. As it is constant, an average for the star signal can be used as ground truth in order to calculate the S/N ratio for the daytime sky brightness, as well as the illuminated lunar surface.
Figure 2: The A-B subtraction of two observations of HD137463. The subtraction removes any dark current or background to leave only a clean positive and negative signal.
Results
The S/N ratio for the a MagJ = 5.423 star are shown in Fig. 3. A sharp decrease in S/N ratio is observed as air-glow begins around solar altitude = -5. The S/N continues to decrease, slowly levelling off around S/N = 15 as the sun reaches solar altitude = 5. This puts the magJ = 5.423 star well above the detectable threshold, and would correspond to a MagR = 6.7 LIF.
Figure 3: Left: The S/N ratio in high gain mode, of HD137463 against the sky background between solar altitudes -10 & -1. Right: The S/N ratio in low gain mode, of HD137463 against the sky background between solar altitudes -1 & -5.
By taking measurements of the lunar background brightness, we can verify the S/N ratio we would expect from these LIF when observed on the lunar surface. Table 1 contains the results from count-averaged observations of the background, and the S/N of the MagJ star if observed against the background, emulating a flash. Again, even against the illuminated bright limb, the S/N ratio is above the detectable threshold, and shows that with this system, we would be able to detect LIFs of MagJ ≥ 5.423, with the possibility of even fainter magnitudes under more favourable conditions.
Table 1: The S/N ratio of the reference star used against different regions on the lunar surface, from darkest to brightest.
| Region | S/N |
| Lunar Night Side | 147 |
| Terminator | 42 |
| Lunar Day Side | 21 |
| Lunar Bright Limb | 19 |
References
[1] Liakos et al (2019) A&A, 633, 29 pp.
[2] Eichhorn (1975) P&SS, 23, 11, 1519-1525
[3] Avdellidou & Vaubaillon (2019) MNRAS, 484, 5212-5222
[4] Wegner et al (2000) A&A, 143, p.9-22
How to cite: Sheward, D., Delbo, M., Avdellidou, C., Cook, A., and Lognonne, P.: J-Band Measurements for All-Hours Lunar Impact Flash Observations, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1077, https://doi.org/10.5194/epsc2022-1077, 2022.
TP15 | Astrobiology
TP17 | Planetary field analogues for Space Research
Introduction:
The interest for the Moon has risen with many missions being planned for the Moon surface culminating to the Artemis missions, spearheading a new era of human presence on the lunar surface. At the same time a recent paper (1) provided an overview of the current state of Martian research and understanding. A common theme on both of these endeavors is the requirement of extensive research across the fields of astrobiology, the frontier of ISRU technologies and habitability research under simulated conditions of those environments. A large number of Lunar and Martian Simulants has been developed over the past decades, often though produced rapidly with lower fidelity to satisfy demand (2). Towards this purpose, our group made an effort to develop such materials, since in Greece only potentially analogue locations for simulated research exists. This research was initiated with the introduction of a new simulant classification system, after having highlighted a number of issues that pertain on the facet of Martian Simulants. We here report on the development of new simulants we produced for the Lunar and Martian surfaces.
Methodology:
Initially, we scrutinised the literature focusing on three focal points of research to collect data on the composition of Lunar and Martian surface location, the Lunar Curator Facility, the Analyst’s Notebook and the respective publications on simulant production, in order to identify which datasets have been already utilised. Based on these data, we selected one Lunar and two Martian locations to produce simulants. For the Moon we selected the 15260 Apollo Sample which has been extensively studied. (3) For Mars, we opted for the Rocknest and Gobabeb targets, which are 2 of the most cited and compared sites for simulant production. More specifically, for Moon we utilised the chemical analysis provided by (3) and for Mars those provided by (4).
For the simulant development we collected a number of igneous rock samples from the field, and acquire a number of pure mineral phases, for use as individual components, presented in table 1. All of the materials utilised by our team in the synthesis of the simulants have been firstly crushed and grounded to a grain fraction of under 1 mm. A portion of the material was further crushed in under 250 μm, and later refined for XRD analysis. Each sample was then scanned in three random locations via SEM-EDS and the average analysis was taken as the sample’s chemistry. Thus, via those two analytical techniques, the background of the chemical and mineralogical make up of our inventory of materials was established.
In order to establish the quality of our simulants we utilised the Figure of Merit (FOM) proposed by (5) and applied by (6). By using this system you can deduce the accuracy of your simulant based on how close the percentages of chemical oxides are to the reference sample.
Simulants:
Up to the point of writing, our team has produced a total of four simulants, two for the Moon and two for Mars. Initially a production of two prototypes for a Lunar and Martian simulant, Simulant #1 and #2 respectively, were made by mixing three individual mineral and rock components to verify the method of synthesis and correct any mistakes. However, even at that stage the theoretical FOM of our Simulant #1 was above 95% when compared to the Apollo 15260 sample, and Simulant #2 for Mars had FOM 90,7% and 89% for the Rocknest and Gobabeb targets respectively. (Table 1)
Based on the preliminary results we produced refined simulants, Simulant #3 and #4 for Moon and Mars respectively, using additional components materials as showed in table 1. Thus, Simulant #3 for the Apollo 15260 sample reached FOM of almost 96% and Simulant #4 for Mars reached FOM of 94,6% and 91,6% for the Rocknest and Gobabeb targets, respectively. (Table 1)
Future Goals:
The goal of this project is to try and make simulant materials for Moon and Mars more accessible to the scientific community, but also provide materials of higher fidelity and accuracy. Based on their chemistry, the FOM values on the martian simulants are higher than those presented in (6), suggesting that our endeavor has significant prospects compared with the fidelity of other simulants and providing the confidence that higher accuracy simulants can be synthesised. Furthermore, an additional number of analytical techniques will be used to verify their fidelity. Additionally, by the acquisition of additional mineral phases and rock samples we are targeting to increasing the FOM values. A short term requirement is also the availability of well-known simulants in order to be used in the OxR ESA project (7).
References:
- H. G. Changela et al., Mars: new insights and unresolved questions. International Journal of Astrobiology, 1-33 (2021).
- G. H. Peters et al., Mojave Mars simulant—Characterization of a new geologic Mars analog. Icarus 197, 470-479 (2008).
- A. Duncan et al. (1975) Interpretation of the compositional variability of Apollo 15 soils. in Lunar and Planetary Science Conference Proceedings, pp 2309-2320.
- C. Achilles et al., Mineralogy of an active eolian sediment from the Namib dune, Gale crater, Mars. Journal of Geophysical Research: Planets 122, 2344-2361 (2017).
- C. Schrader et al. (2009) Lunar regolith characterization for simulant design and evaluation using figure of merit algorithms. in 47th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, p 755.
- L. E. Fackrell, P. A. Schroeder, A. Thompson, K. Stockstill-Cahill, C. A. Hibbitts, Development of Martian regolith and bedrock simulants: Potential and limitations of Martian regolith as an in-situ resource. Icarus 354, 114055 (2021).
- ESA (2022) https://www.esa.int/Enabling_Support/Space_Engineering_Technology/Moon_and_Mars_superoxides_for_oxygen_farming.
Table 1. Simulant components and Figure of Merit percentages.
How to cite: Stavrakakis, H.-A., Argyrou, D., and Chatzitheodoridis, E.: Introducing the First Greek Martian and Lunar Simulants, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-611, https://doi.org/10.5194/epsc2022-611, 2022.
The identification of novel terrestrial sites that are analogous for other planetary bodies is an active area of research within astrobiology, because of the logistical and financial difficulties in obtaining extraterrestrial samples for analysis. Characterisation of potential analogue sites is undertaken to assess how accurately they represent a specific extraterrestrial environment. Analysing their physicochemical conditions and microbial communities are key components of these studies to understand what metabolisms would be viable in such environments.
One such novel analogue environment is the salt plains of Western Sahara. Western Sahara is one of the driest regions on Earth. It is located on the northwest coast of West Africa and is characterised by high UV exposure, low annual precipitation and water activity, subsurface water and high annual temperatures. These features make Western Sahara a potential analogue site for Mars during the Noachian-Hesperian transition period (3.5 – 3.8 Ga), when the atmosphere began to thin and surface water started evaporating (Warner et al., 2010), similar to other terrestrial deserts, such as the Atacama Desert and the McMurdo Dry Valleys.
The hypersalinity, aridity and high UV radiation levels of the Western Sahara salt plains would also be appropriate to study whether dissimilatory sulfur metabolisms would be viable in a Noachian-Hesperian Mars analogue environment. Dissimilatory sulfur cycling refers to the use of inorganic sulfur compounds for energy conservation and it has been recognised as a metabolic strategy of interest for putative martian life (Macey et al., 2020). On Earth, evidence from stable sulfur isotope fractionation has suggested this metabolism emerged early in the history of life (~3.5 Ga). During this period, the conditions on Mars were predicted as being more habitable than present-day, with an active magnetic field, thicker atmosphere and liquid water on the surface.
In this study, molecular and geochemical techniques were used to give first insights into the potential of the Western Sahara salt plains to serve as an analogue of Mars during the Noachian-Hesperian transition period. The microbiology was investigated through cultivation-independent and culture-dependent analyses of salt crystals, sediment and water samples obtained at three sites near Llaayoune (Fig. 1). The chemical nature of the samples was analysed through ion chromatography (IC) and inductively coupled plasma - optical emission spectrometry (ICP-OES).
The geochemical characterisation confirmed the high salinity of the samples and identified that sodium, potassium, magnesium and sulfur were the most enriched elements within all samples. Cultivation-dependent work resulted in the enrichment of a wide range of metabolic strategies from the samples including aerobic heterotrophs, phototrophs and sulfate-reducers. The enrichments from the salt were dominated by strains of Bacillus, whereas sulfate-reducing strains of Clostridium were isolated from the sediment samples. Microscope analysis of phototroph-selective media also indicated that algae and Cyanobacteria were successfully enriched from the samples. 16S rRNA amplicon sequencing results will also be presented to gain further in-depth understanding of the microbial community composition. Additionally, results from quantitative polymerase chain reaction (qPCR) experiment targeting sox and dsr genes will be presented to identify the abundance of genes specific for dissimilatory sulfur metabolisms within the samples.
Preliminary data shows that sulfur cycling is occurring in Western Sahara salt plains. Future characterisation of this environment will involve metagenomic analysis of the samples and genome sequencing of the isolates to identify the key metabolisms underpinning the survival and viability of the microbial community. Comparative studies with other Mars analogue environments will then be undertaken to identify metabolisms that may have been thermodynamically viable in ancient martian aqueous environments.
Figure 1. Location of the sample collection sites. Images were generated with Google Earth Pro.
References
Macey, M. C., Fox-Powell, M., Ramkissoon, N. K., Stephens, B. P., Barton, T., Schwenzer, S. P., . . . Olsson-Francis, K. (2020). The identification of sulfide oxidation as a potential metabolism driving primary production on late Noachian Mars. Scientific Reports, 10(1), 10941. https://doi.org/10.1038/s41598-020-67815-8
Warner, N., Gupta, S., Lin, S.-Y., Kim, J.-R., Muller, J.-P., & Morley, J. (2010). Late Noachian to Hesperian climate change on Mars: Evidence of episodic warming from transient crater lakes near Ares Vallis [https://doi.org/10.1029/2009JE003522]. Journal of Geophysical Research: Planets, 115(E6). https://doi.org/https://doi.org/10.1029/2009JE003522
How to cite: Ilieva, V., Stephens, B., Goodall, T., Ori, G., Read, D., Pearson, V., Olsson-Francis, K., and Macey, M.: Western Sahara salt plains as a potential novel Mars analogue, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1043, https://doi.org/10.5194/epsc2022-1043, 2022.
TP18 | Ionospheres of unmagnetized or weakly magnetized bodies
OPS2 | Exploration of Titan
1. Introduction
Titan is the only moon in our solar system with a substantial atmosphere. It comprises 98% Nitrogen (Niemann et al., 2005), and is rich in hydrocarbon (CxHy) and nitrile (CxHyNz) species. Such species photochemically react to produce organic aerosols which compose a thick orange haze suspended in Titan’s middle atmosphere.
Global Circulation Models (GCMs) predict the meridional circulation in Titan’s stratosphere and mesosphere is dominated by a single pole-to-pole circulation cell for most of the Titan year (Hourdin et al., 1995; Newman et al., 2011; Lebonnois et al., 2012), and observations are broadly consistent with this prediction (Teanby et al., 2012, Vinatier et al., 2015). These models suggest circulation across the stratospheric equator, but this is not entirely consistent with what is observed. Existing studies show a North-South asymmetry in stratospheric haze abundance (Lorenz et al., 1997; de Kok et al., 2010), suggesting a mixing barrier near the equator. Here, we present a radiance ratio method for approximating latitudinal distributions of stratospheric HCN. We apply this to the region +/-30 degN and use HCN as a tracer to investigate the evolution and behaviour of the equatorial mixing barrier over the Cassini mission.
2. Observations
The Cassini spacecraft explored Saturn and its moons from 2004 to 2017. Throughout its 13-year exploration, Cassini performed 127 close flybys of Titan, observing at infrared, visible and ultra-violet wavelengths. One of Cassini’s twelve instruments, the Composite Infrared Spectrometer (CIRS) (Flasar et al., 2004; Jennings et al., 2017; Nixon et al., 2019) collected almost 10 million Titan spectra in the mid and far-infrared ranges (10 – 1500 cm-1), at a varied spectral resolution between 0.5 – 15.5 cm-1. In this study, we analyse low spectral resolution (~15 cm-1) observations collected by two CIRS focal planes, sensitive to wavenumber ranges 600 – 1100 cm-1 (FP3) and 1100 – 1500 cm-1 (FP4). Generally, low spectral resolution observations require shorter scan times so can be performed at a closer approach distance to Titan, hence achieving higher spatial resolution. This allows small spatial variations in atmospheric constituents to be resolved. Low-resolution observations also have good coverage of Titan’s equatorial region throughout the entire Cassini mission (Figure 1).
Figure 1: Mission coverage for the Cassini CIRS low spectral resolution nadir mapping observations.
3. Optimising Line-by-Line Retrieval Efficiency
Line-by-line (LBL) inversions in spectral analysis are computationally expensive. The correlated-k approximation (Lacis and Oinas, 1991) is often used to decrease the computation time of retrievals, but we found that it is not sufficiently accurate for these low spectral resolution and high signal-to-noise ratio observations (Figure 2c, d). In LBL modelling, a key parameter is the underlying spectral grid spacing. Finer grid spacing improves the forward model accuracy, but at a greater computation cost. To improve the efficiency of LBL runs, we determine a maximum grid spacing (Figure 2a, b) for which a LBL inversion will produce a sufficiently accurate spectrum in the shortest computation time. Typically, a single forward model run takes 2 hours for LBL, compared to 2 seconds for k-tables.
Figure 2: Comparison of spectra produced using a correlated-k (k-table) method and a line-by-line (LBL) method at varied spectral grid spacing. Maximum radiance difference (MRD) (a, b, blue line) between spectra produced at varied (0.1 – 0.0001 cm-1) and fine (0.0001 cm-1) grid spacing is assessed against a level of sufficient accuracy (a, b, grey area). The grid spacing determined to be optimal (0.001 cm-1 for FP3, 0.005 cm-1 for FP4) produces an almost identical spectrum to very fine (0.0001 cm-1) grid spacing (c, d) but at a significantly reduced runtime (a, b). A spectrum produced using a coarse grid spacing (0.1 cm-1) is shown for comparison. The spectrum retrieved using k-tables is not sufficiently accurate for these low-resolution observations (c, d).
4. Estimating Stratospheric HCN with a Radiance Ratio
We construct a radiance ratio formula for approximating HCN abundance from CIRS spectra, such that a greater number of observations can be analysed rapidly. Radiance ratios can be a useful tool for approximating gas contributions to a spectrum. They do not have the reliability of full spectral retrievals but require significantly less computation time. We compare the radiance ratio latitude dependence to full LBL retrievals of HCN, for a subset of our observations, to assess the reliability of our ratio method. LBL retrievals are performed using the Nemesis radiative transfer and retrieval code (Irwin et al., 2008) with our pre-determined optimal grid spacing. We calculate the radiance ratio for a set of approximately 20 low spectral resolution mapping observations (3 are shown in Figure 3).
There appears to be a sharp change in HCN abundance near the equator (Figure 3). This hints at a potential mixing barrier in Titan’s stratosphere. Furthermore, the position of this potential barrier appears to migrate over time. We use the results of this study to investigate dynamic processes in the equatorial region of Titan’s stratosphere and its evolution over the entire Cassini mission.
Figure 3: Our radiance ratio calculated for observations acquired on 08/2005 (a), 05/2006 (b) and 07/2012 (c). The radiance ratio is smoothed by fitting splines (Teanby, 2007). The gradient of each smoothed fit is also shown (bottom).
Acknowledgements
This research was funded by the UK Sciences and Technology Facilities Council.
References
de Kok, R., et al. (2010). https://doi.org/10.1016/j.icarus.2009.10.021
Flasar, F. M., et al. (2004). https://doi.org/10.1007/s11214-004-1454-9
Hourdin, F., et al. (1995). https://doi.org/10.1006/icar.1995.1162
Irwin, P., et al. (2008). https://doi.org/10.1016/j.jqsrt.2007.11.006
Jennings, D. E., et al. (2017). https://doi.org/10.1364/AO.56.005274
Lacis, A. A., & Oinas, V. (1991). https://doi.org/10.1029/90JD01945
Lebonnois, S., et al. (2012). https://doi.org/10.1016/j.icarus.2011.11.032
Lorenz, R. D., et al. (1997). https://doi.org/10.1006/icar.1997.5687
Newman, C. E., et al. (2011). https://doi.org/10.1016/j.icarus.2011.03.025
Nixon, C. A., et al. (2019). https://doi.org/10.3847/1538-4365/ab3799
Niemann, H. B., et al. (2005). https://doi.org/10.1038/nature04122
Teanby, N. A. (2007). https://doi.org/10.1007/s11004-007-9104-x
Teanby, N. A., et al. (2012). https://doi.org/10.1038/nature1161
Vinatier, S., et al. (2015). https://doi.org/10.1016/j.icarus.2014.11.019
How to cite: Wright, L., Teanby, N. A., Irwin, P. G. J., Nixon, C. A., and Mitchell, D. M.: Stratospheric HCN and Evolution of a Mixing Barrier in Titan’s Equatorial Region from Low-Resolution Cassini/CIRS Spectra, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-463, https://doi.org/10.5194/epsc2022-463, 2022.
OPS4 | Jupiter and Giant Planet System Science: New Insights From Juno
The grand appearance of Jupiter’s banded atmosphere, coloured with many shades from white to red, whose cloud structure currently remains elusive with no clear single cloud model responsible for this varied appearance. With a general pattern of alternating bright cloudy zones and darker belts, as well as unique regions such as the Great Red Spot, finding a way to model all of these differing appearances with a single model has proven difficult. Jupiter’s atmosphere provides continual challenges when attempting to characterise its cloud structure due to its frequently varying appearance. This leads to differences between every observation meaning that models are constantly having to adapt to be explain these changes. Such changes can be seen in Figure 1, both of these spectra have been extracted for the same region of the Equatorial Zone (EZ) but are not identical due to the changes in appearance over the 3 years.
Recent works [1,2,3,4] have all attempted to model Jupiter’s atmosphere using a universal chromophore (cloud colouring compound), combined with a deeper conservatively-scattering cloud and also a stratospheric haze layer. These works have all been able to model the atmosphere successfully but it has currently not been possible to determine between these differing solutions to find the most likely representation of the atmosphere. As all the different sets ups have several ways to vary cloud structure and chromophore properties among other parameters, they have been able to fit the changes in the observations. Therefore keeping each set up viable even as the atmosphere changes. The current inability to conclude on a favoured cloud structure highlights the highly degenerate nature of this problem.
Utilising new observations and techniques to analyse the data highlights the delicacy of these results as the previous set ups have to be altered in order to produce the desired fit to the new observations once the input have varied slightly. An unchanged fit is shown in Figure 1, where the ideal fit of the EZ in 2018 has been used for 2021 data and is unable to model the spectra as well as for the spectra which it was derived from. Furthermore introduction of a limb viewing technique, as used in [2], has been done for this data. Here we attempt to fit multiple viewing angles simultaneously, which also begins to question the robustness of these results, due to an inability of nadir derived set ups to reproduce the multiple observations as successfully.
Therefore in this work we have begun to attempt to reduce the degeneracy of the problem before utilising the Non-linear optimal Estimator for Multi-variatE spectral analySIS (NEMESIS) radiative-transfer retrieval algorithm [5], to fit to our observations. From this we want to find a vertical cloud structure which is more reproducible using different observations and techniques. It is hoped that reducing one of the degenerate parameters before fitting will allow us to constrain the atmospheric structure more decisively. Furthermore combining this with the limb darkening technique will hopefully allow us to rule out some of the solutions to this highly degenerate problem to find more confidence in the proposed models.
In this work we will present the preliminary results taken from the application of these methods to observations to derive a new atmospheric model which can be compared with past work. Additionally we will present the use of new techniques to determine the ability of previous models to adapt to new observations to see if they are still viable.
Figure 1: Spectra of the Equatorial Zone in both 2018 and 2021 and the spectral fit using the model from [1] derived for the 2018 data.
[1] Braude, A. S., Irwin, P. G., Orton, G. S., and Fletcher, L. N. (2020). Colour and tropospheric cloud structure of jupiter from muse/vlt: Retrieving a universal chromophore. Icarus, 338:113589.
[2] Pérez-Hoyos, S., Sánchez-Lavega, A., Sanz-Requena, J., Barrado-Izagirre, N., Carrión-González, O., Anguiano-Arteaga, A., Irwin, P., and Braude, A. (2020). Color and aerosol changes in jupiter after a north temperate belt disturbance. Icarus, 352:114031.
[3] Dahl, E. K., Chanover, N. J., Orton, G. S., Baines, K. H., Sinclair, J. A., Voelz, D. G., Wijerathna, E. A., Strycker, P. D., and Irwin, P. G. J. (2021). Vertical structure and color of jovian latitudinal cloud bands during the juno era. The Planetary Science Journal, 2(1):16.
[4] Baines, K., Sromovsky, L., Carlson, R., Momary, T., and Fry, P. (2019). The visual spectrum of jupiter’s great red spot accurately modeled with aerosols produced by photolyzed ammonia reacting with acetylene. Icarus, 330:217–229.
[5] Irwin, P. G. J., Teanby, N. A., de Kok, R., Fletcher, L. N., Howett, C. J. A., Tsang, C. C. C., Wilson, C. F., Calcutt, S. B., Nixon, C. A., and Parrish, P. D. (2008). The NEMESIS planetary atmosphere radiative transfer and retrieval tool. , 109:1136–1150
How to cite: Alexander, C. and Irwin, P.: Comparing atmospheric models of Jupiter, can we reduce the degeneracy of this problem?, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-632, https://doi.org/10.5194/epsc2022-632, 2022.
OPS5 | Outer Planet Moons: Environments and Interactions
MITM5 | Machine Learning in Planetary Sciences
InSight seismic data and marsquake catalogue
NASA's InSight seismometer has been recording the seismicity of Mars for over 3 years and to date, over 1300 seismic events were found by the Marsquake Service (MQS) [1,2]. Marsquakes usually have a low signal-to-noise ratio (SNR) and are consequently often hidden or contaminated by the background noise, making their detection and analysis challenging. Local winds interact with the lander and seismometer system and generate noise levels that fluctuate throughout the Martian day and regularly exceed typical event amplitudes. Additionally, extreme temperature changes cause transient high-amplitude spikes [3]. Conventional tools, such as the STA/LTA detectors, perform poorly on this dataset, as the various noise signals often share a common bandwidth and can be similar in duration to marsquakes [3]. Therefore, MQS detects events by manual data review and discriminates them from wind noise [4] by comparing the seismic data to onboard wind measurements if available, or otherwise, to the excitation of wind-driven lander modes. MQS classifies events by their frequency content into low- (<10%) and high-frequency (>90%) event families and assigns a quality based on their locatability (A: highest to D: lowest quality) [1].
Marsquake detection with convolutional neural network
Deep learning methods, and in particular convolutional neural networks (ConvNet) are nowadays routinely used for complex tasks such as speech or visual object recognition [5]. Here, we use a ConvNet architecture designed for image segmentation [6] to detect marsquake energy in the time-frequency domain. We train the ConvNet to predict segmentation masks that pixel-wise identify event and noise energy based on the time-frequency representation of a given waveform. We use the method to detect marsquakes and to decompose their signal in event and noise components. This allows us to estimate the marsquake duration, frequency content, and SNR. We use the ConvNet to extend the MQS catalogue and further highlight its value in removing noise contamination from marsquakes [7]. Since the MQS catalogue is much smaller than typically labelled datasets used in deep learning [7], we create a training set with synthetic events with stochastic waveform modelling [8]. Synthetic events mimic the different MQS event types in terms of frequency content and duration and are combined with recorded InSight noise to include all types of noise.
Results
We run our ConvNet-based detector on the complete 20 samples-per-second dataset (over 900 Martian days) and compare our results to the careful manually curated MQS catalogue: we can detect all high-quality events and the majority of low-quality events - in addition to these, we find many additional low SNR events. We extend the catalogue by ~50% more events, of which the majority belongs to the high-frequency event family. An overview of the MQS events and our new detections is given in Figure 1. Similar to the MQS catalogue, we find many events in the quiet evening periods during the spring and summer of the Martian year 1 and 2, and further increase the number of events during the nights when noise levels are elevated. During the high noise periods (day time and winter), when noise amplitudes are orders of magnitudes above typical event amplitudes, we do not confidently detect events apart from a few that fall into short quieter periods. Our results suggest that the MQS catalogue is essentially complete for high SNR events and further support previous findings [9] on the seasonality of high-frequency events and their increased activity in Martian year 2 compared to year 1.
Figure 1: Overview of seismic noise, catalogued MQS events and new detections from ConvNet: the background of the main figure represents the broadband, vertical component seismic noise level (data gaps shown in white). The symbols indicate different event types belonging to the low frequency (LF, BB) or high frequency family (2.4, HF, VF), and colours indicate the qualities in the MQS catalogue; new detections found with our ConvNet detector are shown with their predicted event family type. The panel on the left side shows the cumulative event count using MQS events (blue) and MQS events and new detections (red). The event numbers are dominated by the high frequency events (corresponding to over 90% of events).
References:
[1] Clinton et al. (2021), 10.1016/j.pepi.2020.106595
[2] InSight Marsquake Service (2022), doi.org/10.12686/a16
[3] Ceylan et al. (2021), 10.1016/j.pepi.2020.106597
[4] Charalambous et al. (2021) 10.1029/2020JE006538
[5] LeCun et al. (2015), 10.1038/nature14539
[6] Ronneberger et al. (2015), 10.1007/978-3-319-24574-4_28
[7] Zhu et al. (2019), 10.1109/TGRS.2019.2926772
[8] Boore (2003), 10.1007/PL00012553
[9] Knapmeyer et al. 10.1016/j.epsl.2021.117171
How to cite: Dahmen, N., Clinton, J., Meier, M.-A., Stähler, S., Kim, D., Stott, A., and Giardini, D.: A Deep Marsquake Catalogue, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1066, https://doi.org/10.5194/epsc2022-1066, 2022.
MITM6 | Planetary space weather
MITM12 | Planetary Missions, Instrumentations, and mission concepts: new opportunities for planetary exploration
SB1 | Asteroid observations and modelling: properties and evolution of individual objects, families, and populations
SB2 | Small bodies from the active Main Belt to the Oort cloud and beyond
SB4 | Computational astrophysics and numerical models of small bodies and planets
SB5 | Tools for characterizing planetary and small bodies surfaces, atmospheres, and dust particles (Imagery, photometry, spectroscopy, spectrophotopolarimetry)
Introduction:
The properties of icy surfaces in the Solar System evolve under the effect of numerous processes either external, internal or induced by the climate. Thanks to spaceborne remote sensing data, we have access to the current microphysical and compositional state of ices (see for instance Cruz Mermy et al 2022, EPSC [1]) but quantifying the numerous mechanisms involved remains challenging. To study these surfaces hard to access, our goal is to build a one-dimensional numerical model of planetary ices evolving over time.
This task consists in creating an unprecedented innovative tool general to many icy surfaces in the solar system, similar to what the SNOWPACK model does for Earth snow evolution (Tuzet et al., 2017 [2]). These simulations would predict ice microphysics within a depth of a few meters evolving on multiple seasons. They will integrate multiple physical processes (heat transfers, phase changes, surface energy balance, ice grains metamorphism and spatial weathering) acting on the ice layers and couple them with each other.
The numerical scheme will be designed to be versatile enough to activate/deactivate each physical process parametrization. When possible, several approximations of each process will be designed in order to better control numerical efficiency versus realism. Several pieces are already present in the literature, but the novelty and extremely promising nature of the present approach is to encompass them all, since they all contribute to the evolution of ices with potentially similar time and length scales.
We would like to present the thermic module which gives the evolution of the temperature profile of the ice for different layers of variable properties. Previous models have been designed to estimate the thermal transfer in the subsurface, such as LMD 1D (Forget et al, 1999 [3]), KRC (Kieffer et al., 2013 [4]), THERMPROJRS (Spencer et al. 1989 [5]). Among them, some have been designed to model Earth snow evolution, such as SNTHERM (Jordan, 1991 [6]) and SNOWPACK (Tuzet et al., 2017 [2]). Here, we propose to follow the standard heat equation but solve it numerically for non-constant heat properties, especially with time and depth dependent thermal inertia.
Methods:
In this model, the boundary condition is given by the energy equilibrium at the surface: the incoming absorbed solar flux is balanced by the black body emission and the heat flux from the ground. The thermic properties of the materials can be depth and time dependent. We have discretized the heat equation in these conditions and solved the system of equations with an implicit solver.
The spatial grid representing space is discretized as a vector which starts at the planet’s surface and ends such that the zero-flux condition at the bottom is respected. In terms of time discretization, we run the algorithm several sideral days, with a thousand timesteps each. The aim is to validate the algorithm by comparing with analytical and standard numerical solutions.
Results
Validation of our algorithm by comparison with well-known analytic solutions of the heat equation is possible in specific conditions. For a material of constant conductivity, density and heat capacity, the one-dimensional heat equation can be solved analytically for a given set of initial and boundary conditions. In particular, for an initial step function profile bounded in a box with no flux at the boundaries, the solution can be expressed as a Fourier Series which is obtained through separation of variables. Results show a perfect fit between the numerical and analytical solutions which proves that our model works well for a material with constant properties (see figure 1).
Figure 1: Comparative evolution of the temperature profiles.
In more complex cases, in particular when the heat conductivity is depth dependent, analytical solutions of the heat equation do not exist. In these cases, validation of the model comes from comparison with experimental data or from other previously well-established numerical algorithms. Here we choose to compare our method with Spencer’s explicit algorithm for realistic planetary surface conditions (Spencer et al. 1989).
To compare these two models, one must make sure that the initial conditions are the same. Notably, the solar flux responsible for the temperature evolution must be equal. In this fairly simple insolation model Spencer chose to approximate the heating of a planet surface by the Sun throughout a sidereal day by a sinusoidal function. The resulting total surface flux is the equilibrium between the solar flux and the surface black body emission. Results show that the two flux are identical (see figure 2).
Figure 2: Evolution of the surface flux during multiple days (Blue).
For the sake of validation, values of density, heat capacity and conductivity were varied as a function of depth by the largest scales allowed by Spencer’s explicit scheme stability criteria (see figure 3).
Figure 3: Depth dependant properties profiles.
These results show that our implicit model is fully compatible with Spencer’s explicit algorithm, without the restrictions of stability (see figure 4). Using an implicit model will greatly help us to choose our own set of parameters.
Figure 4: Comparative evolution of Spencer’s temperature profile (Blue
lines), and our implicit scheme temperature profiles (Red lines).
Conclusion and Perspectives
We implemented an implicit numerical scheme in Python to solve the heat transfer equation in a layered medium. It has been validated by comparison with analytical solutions and a reference numerical implementation. Our implicit scheme solver of the heat equation has the advantage of ensuring stability and convergence regardless of the material’s properties.
Now we plan to extend our simulation by coupling other processes acting on ice microphysics like ice grains metamorphism. We also plan to use this algorithm to retrieve surface properties in infrared and radar wavelength.
References:
[1] Cruz-Mermy et al., 2022, EPSC 2022
[2] Tuzet et al., 2017, The Cryosphere, 11
[3] Forget et al, 1999, JGR, 104
[4] Kieffer et al., 2013, JGR, 118
[5] Spencer et al. 1989, Icarus, 78
[6] Jordan, 1991, Documentation SNTHERM, 89
How to cite: Mergny, C. and Schmidt, F.: Numerical modeling of thermal wave in layered icy surface, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-592, https://doi.org/10.5194/epsc2022-592, 2022.
SB7 | Laboratory measurements of returned Hayabusa2 samples, meteorites and planetary analogues
SB8 | Surface and interiors of small bodies, meteorite parent bodies, and icy moons: thermal properties, evolution, and structure
SB9 | Latest Science Results in Planetary Defence
The impact processes are ubiquitous in the solar system, as one of the fundamental mechanisms driving the evolution of asteroids and comets[1]. From small meteorite impacts to gigantic Moon-forming collisions[2], the impact cratering formation holds key insights pointing out the dynamic history of our solar system from 4.5 billion years ago. Thanks to the rapid progress in numerical modeling and computational resources, high-resolution numerical models offer a powerful framework for expanding our knowledge of the impact cratering phenomena. Meanwhile, planetary defense missions have steeply advanced in characterizing Near-Earth Objects (NEO), such as NASA's upcoming DART mission[3], which will deflect the orbit of Dimorphos through a kinetic impactor. A few years after the DART impact, the Hera mission by European Space Agency (ESA)[4] will rigorously portray the consequences of the collision, from cratering to exploring the interior and dynamics. Several numerical efforts have recently provided significant insights on impact cratering and ejecta dynamics in response to the DART impactor. Raducan et al. (2019)[5], for example, have comprehensively reported several factors that affect the Dimorphos' response, from target layering and strength[6] to the projectile obliquity[7]. In the present study, after verifying our results using the impactor/target constraints[5-7], we have further examined the consequences of DART impact, focusing more on the impact-generated porosity and gravity anomalies. To accomplish this, we performed hypervelocity impact simulations by the iSALE2D shock physics code[8-10] set up for a variety of target scenarios, ranging from low-cohesion gravity-dominated to high-cohesion stress-dominated regimes. Our simulation results shed new light on the detailed picture of cratering formation in the aftermath of the DART impact.
Figure 1: DART impact-generated gravity and density distribution on asteroid Dimorphos.
References
[1] Holsapple, K. A. (1993). The scaling of impact processes in planetary sciences. Annual review of earth and planetary sciences, 21(1), 333-373.
[2] Wada, K., Kokubo, E., & Makino, J. (2006). High-resolution simulations of a Moon-forming impact and postimpact evolution. The Astrophysical Journal, 638(2), 1180.
[3] Michel, P., Küppers, M., & Carnelli, I. (2018). The Hera mission: European component of the ESA-NASA AIDA mission to a binary asteroid. 42nd COSPAR Scientific Assembly, 42, B1-1.
[4] Cheng, A. F., Rivkin, A. S., Michel, P., ... & Thomas, C. (2018). AIDA DART asteroid deflection test: Planetary defense and science objectives. PSS, 157, 104-115.
[5] Raducan, S. D., Davison, T. M., Luther, R., & Collins, G. S. (2019). The role of asteroid strength, porosity and internal friction in impact momentum transfer. Icarus, 329, 282-295.
[6] Raducan, S. D., Davison, T. M., & Collins, G. S. (2020). The effects of asteroid layering on ejecta mass-velocity distribution and implications for impact momentum transfer. PSS, 180, 104756.
[7] Raducan, S. D., Davison, T. M., & Collins, G. S. (2022). Ejecta distribution and momentum transfer from oblique impacts on asteroid surfaces. Icarus, 374, 114793.
[8] Amsden, A., Ruppel, H., and Hirt, C. (1980). SALE: A simplified ALE computer program for fluid flow at all speeds. Los Alamos National Laboratories Report, LA-8095:101p. Los Alamos, New Mexico: LANL.
[9] Collins, G. S., Melosh, H. J., and Ivanov, B. A. (2004). Modeling damage and deformation in impact simulations. Meteoritics and Planetary Science, 39:217--231.
[10] Wünnemann, K., Collins, G., and Melosh, H. (2006). A strain-based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets. Icarus, 180:514--527.
How to cite: Senel, C. B. and Karatekin, O.: Hypervelocity impact simulations of DART on asteroid Dimorphos: Impact-generated porosity and gravity anomalies, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-404, https://doi.org/10.5194/epsc2022-404, 2022.
Asteroids have inhabited the Solar System since its formation, and some of them may pose risks to life on Earth due to the possibility of collision with our planet. The most emblematic case of a catastrophic impact, with very significant implications for life, is the asteroid that struck the Earth 66 million years ago, forming the Chicxulub crater in the Gulf of Mexico, and causing the extinction of about 75% of all life forms on Earth. But despite this and several other events that continue to occur on smaller scales, this theme is rarely addressed by sciences, especially in Brazil. When approached by the press, it is usually under an alarmist and poorly grounded from the point of view of science.
This research aimed to analyze the level of awareness related to the importance of planetary defense among university students, as well as on ways to properly communicate the characteristics and risks related to this phenomenon to society. Besides searching for ways to defend the Earth from a possible future cosmic impact, one of the main goals of Planetary Defense is to make the population aware of its characteristics, frequency of occurrence, risks and consequences.
We focused on this subject using Science communication strategies, such as the creation of an Instagram page, where it was sought and perfected to put together posts about Planetary Defense in a simple way to reach non-specialist audiences. Thus, forms and languages have been sought to convey the facts surrounding meteoritic impacts in a way that they can be understood by the population, thus attracting the necessary attention and avoiding possible misinformation and/or panic.
We employed a semi-quantitative methodology that begins by presenting what asteroids and comets are, showing simulations of large impact events, and detailing physical phenomena arising from encounters between asteroids and the Earth. Measures to protect the planet were also analyzed and how institutions such as NASA (National Space Agency, United States) and ESA (European Space Agency, European Community) have contributed with research and equipment for planetary defense.
In addition, we combined this methodology with a semi-structured survey questionnaire. The survey was aimed at investigating society's perception of the potential risks of impacts of celestial bodies against the Earth, using students enrolled at the State University of Campinas (Unicamp, Brazil). as a sampling population.
The survey´s results refer to a total 150 responses, Fig. 1 shows that the large majority of the UNICAMP’ students don’t have previous knowledge of the concept of Planetary Defense, and that they also do not consider the topic as relevant. This shows the need for awareness dissemination regarding the risk of asteroid impacts, the only natural disaster that can be predicted in advance.
Figure 1: Survey questionnaire about society's perception of the potential risks of impacts of celestial bodies against the Earth.
As part of the study, a series of activities were developed at the University of Campinas to mark Asteroid Day 2022, celebrated annually on June 30th. During two days, a number of guest speakers presented topics related to Planetary Defense to an audience comprising Unicamp´s students and faculty members, as well as the general public, mostly high-school students and school teachers. The results contributed significantly for raising the awareness about planetary defense and for disseminating the scientific knowledge on asteroid impacts and their risk to Earth and to humankind.
Still part of Asteroid Day 2022, a series of interactive activities were developed with children at the city of Campinas Planetarium. These included workshops on rocket launching towards "asteroids", for transmitting the concept of the DART Mission to the kids and their parents. Presentations were also made on general themes about planetary sciences, as well as an astrophotography workshop held at the Campinas Municipal Observatory.
Although the study is still in progress, our preliminary conclusions are that there is very scarce knowledge of what Planetary Defense is, or recognition of its importance, even among higher education students of one of the most prestigious universities in Brazil. This shows how much Planetary Sciences are undervalued, and particularly, the theme of Planetary Defense. We expect that, by the end of this study, adequate ways will be exploited for disseminating knowledge on these topics.
How to cite: Mistro, M. E. T., Crosta, A. P., Costa, J. O. P., and Schmidt, S. C.: Planetary Defense: Public Perception and How to Communicate, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-682, https://doi.org/10.5194/epsc2022-682, 2022.
EXOA1 | Formation, evolution, and stability of extrasolar systems
The size distribution of solids in the protoplanetary disk is still ill constrained [1] but is a vital parameter that influences planetary growth [2]. The typical size and spatial distribution of solids evolves throughout the planet formation process via collisions and radial drift. As the planets grow, they excite the mutual random velocities among planetesimals making their mutual collisions destructive which leads to fragmentation, reducing their typical size. This effect of self-interacting planetesimals has been found to inhibit or favor the formation of planets due to competing effects of easier accretion of smaller fragments and depletion by gas-drag induced drift [3-4]. However, previous studies have either focused on single planets and systems or have neglected concurrent effects like migration.
Therefore, we run planet formation simulations with the generation III Bern model [5] with a Eulerian 1D solid disks. The model tracks the growth and evolution of several planetary embryos from oligarchic growth to the final planetary system. We added to it a fragmentation toy model [6] to see the impact fragmentation has on planet formation. To see its influence on the diverse types of exoplanets we make use of a population synthesis approach to investigate larger parts of the parameter space [7]. This allows us to have a more complete picture of what influence the collisional evolution of planetesimals has on planet formation and to study the effects that arise from its interplay with the formation of multiple planets in the same system.
In figure 1, we show two exemple synthetic planet populations of 1000 systems with (right) and without (left) the added fragmentation model. We find multiple interesting features in our synthetic populations that arise from the fragmentation of planetesimals. The fragmentation lends more importance to specific locations in the disk where growth is enhanced like the ice line and the inner disk. In addition, it enhances the formation of giants.
In conclusion, there are significant differences in synthetic populations when including or neglecting fragmentation. This suggests that the addition of fragmentation to global planet formation models is important as a self-consistent solid disk description is vital to understand planet formation.
In figure 1. Comparison of a synthetic exoplanet population without (left) the added fragmentation model and one with (right). The semi major axis (in AU – log scale) is plotted on the x-axis and the planetary mass (in Earth masses – log scale) on the y-axis. Both populations are shown at an age of 5 Gyr. The Red points refer to planets with more envelope than core mass, the blue ones are icy planets (ice mass fraction larger than 1%) and the green points are rocky planets (ice mass fraction smaller than 1%).
References:
[1] Helled, R. & Morbidelli, A. 2021, in ExoFrontiers (IOP Publishing)
[2] Fortier, A., Alibert, Y., Carron, F., Benz, W., & Dittkrist, K.-M. 2012, A&A, 549, A44
[3] Guilera, O. M., de Elía, G. C., Brunini, A., & Santamaría, P. J. 2014, A&A, 565, A96
[4] Chambers, J. 2008, Icarus, 198, 256
[5] Emsenhuber, A., Mordasini, C., Burn, R., et al. 2021, A&A, 656, A69
[6] Ormel, C. W. & Kobayashi, H. 2012, The Astrophysical Journal, 747, 115
[7] Emsenhuber, A., Mordasini, C., Burn, R., et al. 2021b, A&A, 656, A70
How to cite: Kaufmann, N. and Alibert, Y.: A population level study on the influence of planetesimal fragmentation on planet formation, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-135, https://doi.org/10.5194/epsc2022-135, 2022.
EXOA2 | The hidden newly born planets
EXOA4 | Interiors and Atmospheres of Rocky Planets: Formation, Evolution and Habitability
The Habitable Zone (HZ) can be considered plainly as a measure of the potential of planetary habitability or as the parametric region about a star in which surficial water is deemed to be stable on a planet. This potential stability is a direct result of host star flux and effective radiative cooling mechanisms in accordance with the atmospheric greenhouse effect of orbiting planets. This stellar flux varies in conjunction with the temporal evolution of the host star.
Hence, we conduct the modelling of the Main Sequence (MS) and pre-MS phases of HZ evolution in order to characterise the habitability of 6 exoplanetary systems with FGK-Type host stars. In addition to this, 1 M⊙ hypothetical stars were modelled with fluctuating albedo and metallicity values to characterise the relationship of certain stellar and planetary parameters on temporal HZ evolution, to better calibrate the characterisation of exoplanet habitability in general for a diverse range of planets. This is a tool to allow us to make predictions about when or if these planets modelled are potentially habitable now, have previously been or will be in the future.
Our model simulations allow us to recommend certain exoplanets for further characterisation due to their potential current (or previous) orbit within their respective HZ, assuming they are currently considered or found to be rocky planets. These planets include Tau Ceti e, HD 40307g, Kepler 62f and e. Techniques that could be used to investigate these planets may be characterisation of their atmospheres for biosignatures using modelling of atmospheric composition to evaluate their habitability further, as situation within the HZ does not necessarily mean a planet is habitable. HZ planets, in relatively close proximity to the Earth and situated far enough from their host star to be resolved, should be probed using direct imaging to investigate surface environments, critical near-surficial conditions that may influence the stability of liquid water.
Potential future telescopes suitable for these recommendations would be the Habitable Exoplanet Imaging Mission (HabEx) and the Large Ultraviolet Optical Infrared Surveyor (LUVOIR) (Arney et al., 2018).
A major conclusion from the investigation of a 1 M⊙ hypothetical star reveals the potential for a closer inner HZ edge than formerly estimated (0.325 AU from the host star when albedo (A) = 0.9 in this work). The repercussions of this updated estimate imply that if a closely orbiting planet with a high albedo is found to orbit its host star, it may still be habitable and should not be neglected in terms of its habitability prospects. This also extends the frequency of habitable exoplanets if the inner edge of the HZ truly can exist at close proximity to the host star in question, having repercussions on exoplanet characterisation as a whole if these HZ distances can be replicated in subsequent works or verified by rocky exoplanet observations.
Furthermore, our results reinstate that a tidal-locking scenario is likely to shorten the width of the HZ significantly and draw it closer to the host star – introducing constraints for rocky bodies that may be considered habitable. This is significant when considering planets orbiting beyond the inner edge of the HZ and re-evaluation of their habitability may be necessary once atmospheric, albedo and other orbital data for exoplanetary systems can be determined.
Previous HZ publications have centred around MS habitability (Kasting et al., 1993; Kopparapu et al., 2013), yet the temporal evolution of the HZ is becoming more widely recognised as fundamental in evaluating habitability as a whole (Ramirez and Kaltenegger, 2014; Danchi and Lopez, 2013). Pre-MS evolution is a deciding factor as to whether planets are still habitable during the MS phase – planets within the pre-MS HZ are unchartered targets in the search for habitable worlds or even as tools to decipher habitable planet diversity and early water delivery mechanisms. Such results should be utilised as a first order estimation of exoplanetary habitability.
To summarise, there is still significant progress left to be made in calculating reliable HZ boundaries and to then characterise the habitability of planets orbiting within them. Nevertheless, these HZ boundaries serve as a critical basis for the assessment of the habitability of modelled exoplanetary systems. Such works are beneficial as they may result in the detection of habitable exoplanets suitable for observational follow-ups, or even to the eventuality of discovering evidence for extra-terrestrial life.
References:
- Arney, G., Batalha, N., Cowan, N., Domagal-Goldman, S., Dressing, C., Fujii, Y., Kopparapu, R., Lincowski, A., Lopez, E., Lustig-Yaeger, J. and Youngblood, A., 2018. The Importance of Multiple Observation Methods to Characterize Potentially Habitable Exoplanets: Ground-and Space-Based Synergies. arXiv preprint arXiv:1803.02926.
- Danchi, W.C. and Lopez, B., 2013. Effect of Metallicity on the Evolution of the Habitable Zone from the Pre-main Sequence to the Asymptotic Giant Branch and the Search for Life. The Astrophysical Journal, 769(1), p.27.
- Kasting, J., Whitmire, D. and Reynolds, R., 1993. Habitable Zones around Main Sequence Stars. Icarus, 101(1), pp.108-128.
- Kopparapu, R., Ramirez, R., Kasting, J., Eymet, V., Robinson, T., Mahadevan, S., Terrien, R., Domagal-Goldman, S., Meadows, V. and Deshpande, R., 2013. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES. The Astrophysical Journal, 765(2), p.131.
- Ramirez, R.M. and Kaltenegger, L., 2014. The habitable zones of pre-main-sequence stars. The Astrophysical Journal Letters, 797(2), p.L25.
How to cite: Hogan, J.: Characterising the Potential for Planetary Habitability: A Study of the Temporal Evolution of Exoplanet Habitable Zones, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-369, https://doi.org/10.5194/epsc2022-369, 2022.
EXOA5 | Devolatilization During Rocky (Exo)planet Formation: Mechanisms, Simulations, and Observations
The ICAPS experiment (Interactions in Cosmic and Atmospheric Particle Systems) was part of the Texus-56 sounding rocket flight in November of 2019. ICAPS studies the agglomeration of 1.5 µm-sized, monomeric silica grains under microgravity conditions, as would be present in the early stages of dust growth in protoplanetary disks, which our study aims at describing.
For this, a cloud of dust was injected into a vacuum chamber with ~7000 monomer grains per mm³. A thermal trap was then utilized to stabilize the dust cloud against any external disturbances during the flight. Two overview cameras and a long-distance microscope with a high-speed camera were used for the in-situ observations of the particles (see Figs. 1 and 2).
This talk focuses on the data analysis and results of ICAPS, in particular with respect to Brownian motion and aggregate growth. From the total experiment time of six minutes of almost perfect weightlessness, we extracted the masses and translational friction times of 414 dust aggregates from their translational Brownian motion. For a subset of 69 of these particles, we were also able to derive their moments of inertia and rotational friction times from their Brownian rotation. With these data, we derived a fractal dimension close to 1.8 for the ensemble of dust aggregates. We compared this unambiguous physical method for the determination of the fractal dimension with an optical approach, in which the mass is derived through the particle extinction and the moment of inertia is derived from the microscopic images.
The combination of both methods then facilitates the growth analysis, for which the overview cameras were also used. We observed an initial rapid, charge-induced growth of aggregates, which was followed by a slower growth rate, which was dominated by ballistic cluster-cluster agglomeration. As a surprise, around 100 seconds into the flight, clear indication for runaway growth (or the onset of gelation) was observed.
Fig. 1: Examples of dust aggregates from the long-distance
microscope images.
Fig. 2: Image from one of the overview cameras after 100 s of experiment time (1024 x 768 pixels, about 12 x 9 mm²).
How to cite: Schubert, B., Molinski, N., Blum, J., Glißmann, T., Pöppelwerth, A., von Borstel, I., Balapanov, D., Vedernikov, A., Houge, A., and Krijt, S.: ICAPS: Dust aggregate properties and growth derived from Brownian translation and rotation from the ballistic to the diffusive limit, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-581, https://doi.org/10.5194/epsc2022-581, 2022.
EXOA7 | Future instruments to detect and characterise extrasolar planets and their environment
EXOA9 | Towards better understanding planets and planetary systems diversity
A central question in exoplanetary research is the characterisation of the composition and internal structure of exoplanets. However, the observable parameters of an exoplanet are scarce and generally limited to the planet’s mass and radius and the properties of its host star. This means that it is not possible to fully constrain the internal structure parameters of an exoplanet, such as the iron core mass fraction, the presence of a water layer or the amount of gas, from these observations: The problem is intrinsically degenerate [1,2].
To overcome this difficulty, a Bayesian inference scheme is used, which is an inverse method based on Bayes’ theorem. It updates the previously assumed probability of the internal structure parameters (the prior) based on the probability of the observation given the same parameters (the likelihood), returning the posterior distribution of these parameters.
In our case, the likelihood is determined based on an internal structure model, which calculates the radius of a planet with a given mass and composition based on the planetary structure equations as described in [6]. This calculated radius and the transit depth it implies are then compared to the observed transit depth of the real planet. For the internal structure model, we use the BICEPS code as described in [4] and based on [2,3] to model the core, mantle and water layers of the planet; the atmosphere is modelled separately according to [5]. For the composition, we assume that the planetary composition matches the one of the star exactly [7].
We developed a full grid approach that has multiple advantages over the traditionally used scheme based on Markov chain Monte Carlo methods. To compensate for the higher number of sampling points that such a brute force approach requires, we trained a deep neural network to replace the internal structure model, which significantly reduces the computation time of the model. Additionally, we take into account that the measured masses and radii of the planets in the same system are correlated, since they were measured relative to the same star. This allows for an increase in computation time that is only linear when adding an additional planet. The full approach including the internal structure model is described in more detail in [8].
This method has already been used to characterise the internal structure of various exoplanets observed by the CHEOPS mission, e.g. [8] and [9] (and more submitted). As an example, Figures 1 – 4 show the internal structure of TOI-561 b, c, d and e, calculated using the planetary and stellar parameters published in [9]. Note that the corresponding figures in [9] showing the posteriors of the internal structure parameters unfortunately do not use the published stellar parameters, see [10] for more details.
Figure 1. Posterior distribution of the most important internal structure parameters of TOI-561 b using the planetary and stellar parameters published in [9]. The shown parameters are the core and water mass fractions of the solid planet, the molar fractions of Si and Mg in the mantle and Fe in the core and the gas mass of the planet in Earth masses in a logarithmic scale. The dashed lines show the 5 and 95% quantiles, while in the titles the median and the 5 and 95% quantiles are shown.
Figure 2. Same as Figure 1 but for planet TOI-561 c.
Figure 3. Same as Figure 1 but for planet TOI-561 d.
Figure 4. Same as Figure 1 but for planet TOI-561 e.
References:
[1] Rogers, L. & Seager, S. 2010, The Astrophysical Journal, 712, 974
[2] Dorn, C., Khan, A., Heng, K., et al. 2015, A&A, 577, A83
[3] Dorn, C., Venturini, J., Khan, A., et al. 2017b, A&A, 597, A37
[4] Haldemann, J., et al. (in prep.)
[5] Lopez, E. D. & Fortney, J. J. 2014, ApJ, 792, 1
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How to cite: Egger, J. A., Alibert, Y., Haldemann, J., and Venturini, J.: A Neural Network Based Approach to Modelling the Internal Structure of Transiting Exoplanets and Its Application to Planets Observed by the CHEOPS Mission, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-320, https://doi.org/10.5194/epsc2022-320, 2022.