SB6
Session assets
Discussion on Slack
Oral and Poster presentations and abstracts
Asteroids, along with other small bodies are what is left of the original planetesimal disk from the planet-formation era. But not all asteroids that we observe today are planetesimals. Many of those planetesimals, during the history of the solar system, were destroyed by impacts, creating families of smaller asteroid fragments, which make the vast majority of the current main belt population. However, very few of these collisional fragments are actually linked to known families. The smaller are the sizes of the family members, the more numerous they are. Moreover, due to non-gravitational forces, known as the Yarkovsky effect, the members of these families move away from the original location with a velocity proportional to 1/D, where D is the asteroid diameter. These two facts result in that the smaller are the studied asteroids the more confusing is the picture of the original compositional distribution.
Our team developed a novel methodology to identify the planetesimals in the main belt (Bolin et al., 2017, Delbo' et al., 2017, 2019, 2021), based on finding asteroid families from correlations between their 1/Diameter and their semi-major axis (this is the so-called V-shape of asteroid families). By removing all asteroids that are inside these V-shapes and thus belong to families, we revealed the planetesimal population. This new analysis has now been completed in the Inner Main Belt (IMB) between 2.1 and 2.5 au with the identification of 71 planetesimals.
We started a spectroscopic survey of the identified IMB planetesimals, aiming at constraining their composition and mineralogy, information that is of paramount importance for defining the original compositional gradient of the main belt, including that of materials of high exobiological interest, such as hydrated minerals and carbonaceous compounds.
The survey was mainly carried out at the 1.82m Copernico Telescopio (Asiago, Italy) for spectroscopy in the visible range, and at the 4.2m Lowell Discovery Telescope (Flagstaff, USA) and 3.2m NASA Infrared Telescope Facility (Mauna Kea, USA) for the near infrared range (0.95-2.3 micron). Few data come from unpublished observations at the 3.6m New Technology Telescope (La Silla, Chile) and the 1.22m telescope in Asiago made previously by our team. The new data presented here come from 14 distinct observing runs spread out between 1999 and 2020.
To complete the survey of the IMB planetesimals, we also used spectra in the visible and NIR range published in the literature. In fact, several of the identified planetesimals are relatively large and bright, and already studied in spectroscopy.
After standard spectral reduction procedures, we merged the visible and near-infrared spectra (when available) of a given target to obtain a full VIS+NIR spectrum and we perform the taxonomic classification following the Bus-DeMeo taxonomy (Bus et al., 2002; DeMeo et al., 2009) using the M4AST tool (http://m4ast.imcce.fr) (Popescu et al., 2012). A visual inspection to identified the presence of absorption bands characteristic of some classes was performed to strength the taxonomic classification. In addition, we compute for each planetesimal several spectral parameters, such as spectral slopes, and center, depth and minimum of absorption bands, when present. Finally, we used the RELAB database (Pieters, 1983), to look for meteorite analogues of each planetesimal.
As expected, we found that the majority of the IMB planetesimals belongs to the S-complex (about 50 %, Fig. 1). The population also includes 20% of X-complex, 18 % to C-complex and 12% of end members (D, K, L and V-type). Interestingly, our survey reveals that more than 60% of the IMB carbonaceous-rich planetesimals belong to the Ch/Cgh types, as they show features associated to hydrated materials, indicating the presence of water ice at relatively small heliocentric distances. Surprisingly, about 4% of the planetesimals belong to the D-type, which are usually located in the outer Main Belt and in the Jupiter Trojan swarms. Finally, no olivine-rich A-type planetesimal is found. A-types are supposed to be formed by the collisional exposure of a mantle of a differentiated parent body. The fact that they are absent in the IMB planetesimal population supports the aforementioned theory of the A-type origin.
Here we will present the spectroscopic and compositional results of the IMB planetesimals as well as the implications for planetary formation models.
Figure 1 : The spectroscopic distribution of the studied planetesimals using the Bus-DeMeo taxonomy.
References : Bryce T. Bolin et al., Icarus, Volume 282, 2017, Pages 290-312 ; Marco Delbo et al., Science : 1026-1029, 2017 ; Marco Delbo et al., A&A 624 A69 (2019) ; Schelte J. Bus et al., Icarus, Volume 158, Issue 1, 2002, Pages 146-177 ; Francesca E. DeMeo et al., Icarus, Volume 202, Issue 1, 2009, Pages 160-180 ; M. Popescu et al., A&A 544 A130 (2012) ; Pieters, C. M. (1983), J. Geophys. Res., 88( B11), 9534– 9544,
How to cite: Bourdelle de Micas, J., Fornasier, S., Delbo, M., Avdellidou, C., and Van Belle, G.: A survey of Inner Main Belt planetesimals : composition and mineralogy, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-198, https://doi.org/10.5194/epsc2021-198, 2021.
Asteroids are the remnant blocks of the early stages of the formation of our Solar System. In particular, those classified as “primitive” are believed to contain the most pristine and almost unprocessed materials (water-bearing minerals, carbon compounds, and organics), and therefore they provide unique information on the formation and evolution of our planetary system, including how water appeared on Earth. Among these objects, primitive near-Earth asteroids (NEAs) are of particular interest. Due to their proximity they are impact hazards to Earth, but they are also the ideal targets for space missions. That is the case of primitive NEAs (101955) Bennu and (162173) Ryugu, primary targets of NASA’s OSIRIS-REx and JAXA’s Hayabusa 2 sample return missions, respectively, currently on their way to encounter the two asteroids. The main asteroid belt, located between the orbits of Mars and Jupiter (2.1-5.2 AU), and in particular collisional families, are currently considered the principal source of NEAs (Bottke et al. 2002; Bottke et al. 2005). In the case of the two primitive NEAs mentioned above, several studies have shown that the most likely source is the Polana collisional family (Campins et al. 2010, 2013), a primitive family located in the inner belt. Other large primitive families in that region are Erigone, Sulamitis, and Clarissa. Smaller primitives families like Klio, Chaldaea, Svea and Chimaera can also be found in the same region (Nesvorny et al. 2015).
With the main objective of supporting the science return of OSIRIS-Rex and Hayabusa 2, in 2010 our group started a coordinated effort to characterize the surface composition of primitive asteroids not only in the collisional families of the inner belt, but in the central and outer belt: our PRIMitive Asteroids Spectroscopic Survey (PRIMASS) includes both visible and near-infrared spectra. Up to now, in the frame of PRIMASS, our group has studied several primitive families wihtin the inner main belt: the Polana-Eulalia complex (de León et al. 2016; Pinilla-Alonso et al. 2016), Erigone (Morate et al. 2016), Sulamitis and Clarissa (Morate et al. 2018a), and Klio, Chaldaea, Chimaera, and Svea (Morate et al. 2019). One interesting result was that Erigone. Sulamitis, Klio, Chaldaea, and Chimaera, presented different percentages of asteroids with an absorption band centered at 0.7μm and associated to hydrated silicates, while the Polana, Clarissa, and Svea families showed no signs of hydration. This result remarks the need for spectral characterization as even the families classified all a priori as primitive can show compositional differences.
Continuing with our PRIMASS survey, we started the characterization of the families in the central part of the belt (2.50-2.82 AU). According to Nesvorný et al. (2015), there are at least 5 primitive families in that region, and for the present work we have focused on three of them: Padua, Nemesis, and Hoffmeister. As it can be seen in Fig. 1A, they overlap in the (a, i) orbital parameter space, and two of them overlap even in the (a, e) space. This might be indicative of a common origin and interestingly, the three families show a similar age. They also overlap in the (a, H) space (Fig. 1B), which make them an ideal case to see if we can discriminate between members from each family using spectroscopy. According to the taxonomical classification of their largest member using visible spectra, Hoffmeister is classified as a CF type family (neutral to blue spectral slope), Nemesis is a C-type family (neutral slope), and Padua is an X-type (redder slope). The distribution of WISE albedos (Mainzer et al. 2011) of Hoffmeister is rather different from what is seen on Nemesis and Padua (Fig. 1C), also indicative of different composition. Only spectra will help to compositionally characterize these families and to search for the presence of the 0.7 μm absorption band associated to hydration. This will allow us to compare the level of hydration in families from the inner to the outer belt (De Prá et al. 2017) and map the water inventory of the asteroid belt to constrain evolutionary models.
Figure 1: A) Distribution of the members of the three primitive collisional families in semimajor axis (a) vs. Eccentricity (top panel) and sine of inclination (bottom panel). The three families clearly overlap in the (a,i) space. B) Distribution of the three families in the absolute magnitude (H) - a space. There are clear overlapping regions where we can test if members of each family can be identified using spectra. C) Distribution of the albedos measured by WISE for the members of the three families.
In order to study these three families, we obtained visible spectra for a total of 124 asteroids (44 within the Nemesis and Hoffmeister families, and 36 within the Padua family) using the OSIRIS spectrograph at the 10.4m GTC, located at the Observatorio Del Roque de Los Muchachos (La Palma, Spain). In this work, we will present the first spectroscopic study of the Nemesis, Hoffmeister, and Padua families, and we will compare the results with those obtained for the families located in the inner main belt.
How to cite: Morate, D., de León, J., Licandro, J., de Prá, M., Pinilla-Alonso, N., Campins, H., and Cabrera-Lavers, A.: PRIMASS visits the primitive collisional families in the central asteroid belt:Nemesis, Hoffmeister, and Padua, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-424, https://doi.org/10.5194/epsc2021-424, 2021.
Organic materials are crucial for understanding the processes that took place at the early stages of Solar System formation and can bring some inputs on the origin of life on Earth. Organics is widely present in various groups of carbonaceous chondrite meteorites that are believed to be originated from dark primitive asteroids [1]. The absorption bands at 3.38, 3.42, and 3.47 µm are assigned to symmetric and asymmetric modes of CH3 and CH2 groups [2]. Thus, the identification of organic materials on the surface of low-albedo objects is rather difficult due to the fact that organic compounds have characteristic features outside the most accessible spectral region (0.4-2.5 µm). Furthermore, there is an overlap between organic and carbonate absorption bands [e.g., 3]. Up to now, the presence of organic band was detected only for a handful of objects, such as (1) Ceres [4], (24) Themis [5], (52) Europa [6], (65) Cybele [7], (121) Hermione [8], and (704) Interamnia [9]. The presence of organic features was also detected on the surface of the comet 67P/Churyumov-Gerasimenko [10].
In this work we studied the available spectra of low-albedo asteroids in order to find the signs of an absorption feature around 3.4 µm band and to examine the occurrence of organic matter on asteroid surfaces. We found 122 published spectra for 92 low-albedo asteroids which cover the range of 3-4 µm. Following spectra classification by [11], the majority of objects in the sample belong to the C-complex group. The rest of the objects belong to X-group, D-group, and T-group. We reduced our sample to 41 objects for which good-quality spectra were available. The presence of an absorption feature at 3.4 µm is detected for 20 asteroids (Fig. 1). As could be seen from the figure, the organic band is found for all asteroids in the sample that are larger than ~250 km, which is most probably related to a higher S/N ratio.
The band parameters such as central position and depth were calculated by fitting a 3.4 µm band with an Exponentially Modified Gaussian (EMG) following the method described in [12]. We found no correlation between the depth and position of the 3.4 µm band and the orbital elements of the asteroids.
Fig. 1. Diameter vs. S/N ratio in the 3.3-3.5 μm wavelength range for dark asteroids in our ample.
Spectral types are not distributed evenly among objects with and without a band around 3.4 µm: all the spectra, except (121) Hermione, not showing the 3.4 µm band belong to the Ch or Chg classes, whereas asteroids with a detected band mostly belong to C, B, and P types. However, only two Ch/Chg asteroids in the sample, (51) Nemausa and (78) Diana, have high S/N spectra. Thus, the absence of the organic band for Ch and Cgh type asteroids can be related to the generally lower S/N ratio and/or a shallower organic band for these groups. Furthermore, there is a tendency for asteroids with the 3.4 µm band to have redder J-K colors and more neutral U-V colors (Fig. 2, left). Additionally, there is a trend for asteroids with a detected 3.4 µm band to have lower albedo (Fig. 2, right).
Fig. 2. U-V vs. J-K colors (left) and U-V vs. albedo value taken from the AKARI survey (right). The largest asteroids in the sample (1) Ceres and (2) Pallas are not shown in the plots.
Acknowledgements. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870403.
References
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[2] Moroz, L. V., Arnold, G., Korochantsev, A. V., Wäsch, R. Icarus, 134,25, 1998.
[3] Alexander, C., Cody, G., Kebukawa, Y., et al. Meteoritics and Planetary Science, 49, 503, 2014.
[4] De Sanctis, M. C., Vinogradoff, V., Raponi, A., et al. MNRAS, 482, 2407, 2019.
[5] Rivkin, A. S., Emery, J. P. Nature, 464, 1322, 2010.
[6] Takir, D., Emery, J. P. Icarus, 219, 641, 2014.
[7] Licandro, J., Campins, H., Kelley, M., et al. A&A, 525, A34, 2011.
[8] Hargrove, K. D., Kelley, M. S., Campins, H., Licandro, J., Emery, J. Icarus, 221, 453, 2012.
[9] Usui, F., Hasegawa, S., Ootsubo, T., & Onaka, T. PASJ, 71, 1, 2019.
[10] Raponi, A., Ciarniello, M., Capaccioni, F., et al. Nature Astronomy, 4, 500, 2020.
[11] DeMeo, F. E., Binzel, R. P., Slivan, S. M., & Bus, S. J. Icarus, 202, 160, 2009.
[12] Potin, S., Manigand, S., Beck, P., Wolters, C., Schmitt, B. Icarus, 343, 113686, 2020.
How to cite: Hromakina, T., Barucci, M. A., Belskaya, I., Fornasier, S., Merlin, F., and Praet, A.: Investigation of the 3.4 µm absorption band in the spectra of low-albedo asteroids, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-199, https://doi.org/10.5194/epsc2021-199, 2021.
Abstract
In this work, we present the experimental phase function and degree of linear polarization of two
sets of samples consisting of forsterite and spinel particles. The size distributions of the studied
samples span over a broad range in the scattering size parameter domain. This work is part of
an ongoing experimental project devoted to understand photopolarimetric observations of asteroids
and comets. In particular, we study the effect of the size on the scattering matrix elements, finding
a strong dependence of characteristic parameters, e.g. maximum of polarization and inversion angle,
on particles size.
Introduction
Polarimetric observations of dust clouds are a powerful tool in planetary science. They allow us
investigating the nature and properties of solar system bodies and planetary systems in different
stages of evolution, e.g. asteroids, comets, and protoplanetary disks. For example, they can be
used as a reference to refine the taxonomic classification of asteroids [1, 2] or they can help in the
discrimination of objects with cometary origin [3]. Some dust materials, like olivine and spinel,
are remarkably interesting for the investigation and characterization of solar system small bodies.
In particular, olivine is an extensively diffuse silicate mineral and spinel, a magnesium/aluminum
mineral, is a characteristic component of the unusual class of presumably ancient Barbarian asteroids
as well as an important component of Calcium Aluminium rich Inclusions (CAI) found in primitive
meteorites [6, 7]. Physical and optical properties of the dust, such as their refractive index, size,
composition, and structure define their ability to scatter the light. Therefore, in order to study these
materials, we need to experimentally characterize their photopolarimetric curves.
Measurements
We analyze six samples of olivine and spinel with different sizes. The samples denoted as Pebble
consist of millimeter-sized grains and lie in the geometrical optics regime. Further, two size
distributions consisting of particles smaller than 30 and 100 micrometers are produced out of the
olivine and spinel bulk samples. The measurements have been performed at the IAA Cosmic Dust
Laboratory (CODULAB), Granada, Spain [4]. The instrument allows to measure the scattering
matrix of a cloud of particles and can be set also to retrieve the scattering matrix of single mm-sized
particles [5]. The measurements have been obtained at 520 nm for the mm-sized grains and at 514
nm for the micron-sized samples. The scattering angle covers the range from 3° to 177°.
Results
Figures 1 and 2 show the phase function and degree of linear polarization (DLP) respectively of
olivine and of spinel samples.
The phase function curves show a strong dependence on particle size. We see that the micron-sized
samples have lower values with a rather flat trend at side- and back-scattering regions and a strong
increase in the forward direction. In contrast, the pebbles show u-shaped phase functions. The slope
of the phase function at side- and back-scattering regions is stronger in the case of the spinel.
The DLP curves also show a dependence on the size. They have the typical bell shape with a
negative branch at low phase angles. Spinel Pebble shows the higher maximum of polarization. The
three spinel samples show a well-defined negative polarization branch with an inversion angle located
around 28° regardless of the particle size. It is interesting to note in the case of the olivine samples
the inversion angle is highly dependent on particle size. The high inversion angle of Barbarian
asteroids polarization curves could be related to the presence of spinel in the form of millimeter
grains of regolith.
Figure 1: Phase function curves (left) and degree of linear polarization (right) for the three olivine
samples.
Figure 2: Phase function curves (left) and degree of linear polarization (right) for the three spinel
samples.
References
[1] Belskaya I.N. et al., Refining the asteroid taxonomy by polarimetric observations. ICARUS, Vol.
284, pp. 30-42, 2017.
[2] López-Sisterna C. et al., Polarimetric survey of main-belt asteroids. VII. New results for 82
main-belt objects. A&A, Vol. 626, A42, 2019.
[3] Cellino A. et al., Unusual polarimetric properties of (101955) Bennu: similarities with F-class
asteroids and cometary bodies. MNRAS, Vol.481, pp.L49-L53, 2018.
[4] Muñoz O. et al., Experimental determination of scattering matrices of dust particles at visible
wavelengths: The IAA light scattering apparatus. JQSRT, Vol. 111, 187 196, 2009.
[5] Muñoz O. et al., Experimental Phase Function and Degree of Linear Polarization Curves of
Millimeter sized Cosmic Dust Analogs ApJSS, Vol. 247, pp.19, 2020.
[6] Cellino A. et al., A successful search for hidden Barbarians in the Watsonia asteroid family.
MNRAS, Vol. 439, L75-L79, 2014.
[7] Devogéle M. et al., New polarimetric and spectroscopic evidence of anomalous enrichment in
spinel-bearing calcium-aluminium-rich inclusions among L-type asteroids. ICARUS, Vol. 304,
pp. 31-57. 2018.
How to cite: Frattin, E., Muñoz, O., Jardiel, T., Gómez Martín, J. C., Moreno, F., Peiteado, M., Tanga, P., Libourel, G., and Cellino, A.: Experimental phase function and degree of linear polarization of mm-sized and micron-sized olivine and spinel particles., Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-236, https://doi.org/10.5194/epsc2021-236, 2021.
Asteroids with an average heliocentric distance of 1 au present special challenges to surveys. Because of the very slow Earth-relative net motion from one orbital revolution to the next, they can remain far from our planet and close to the Sun's location in the sky (Fig 1). For this reason, the likelihood of discovering objects for this type should be generally lower than for other near-Earth asteroids (NEAs). Observational incompleteness for these Earth coorbitals was quantified by Tricarico (2017) and is now readily apparent in the NEA inventory as a deficit of asteroids with a semimajor axis of 1 au (Fig 2).
Figure 1: Illustration of Earth-relative motion of an asteroid with a = 1.001 au and initially 180o away in orbital mean longitude. The asteroid is initially located behind the sun as seen from Earth and drifts towards the Earth’s location at a rate of 0.5o/year. After 180 yr, solar elongation has increased from 0 to 45o.
Figure 2: Number of NEAs in the NEODYS database (https://newton.spacedys.com/neodys/) on 16 May 2021 as a function of semimajor axis counted with a bin size of 0.02 au. Only asteroids with 1-sigma semimajor axis uncertainty of 0.001 au or better were included. The error bars correspond to Poisson counting statistics for each bin. Note the lack of asteroids with a semimajor axis of 1 au.
We have constructed a simple survey simulator to understand how this bias behaves for different asteroid orbits. The relative longitude λ - λEarth between the Earth and the asteroid is a key parameter determining whether an asteroid is discovered or not, affecting even bright asteroids that should otherwise be easy to discover even far from the Earth. Figure 3 shows the observational completeness for H=14 (D=4 km for pv=0.25) asteroids on a 40-yr synthetic survey down to a limiting magnitude of V=20.7 and a solar elongation cutoff of 70o. At a=1 au - the exact co-orbital condition - the asteroid is stationary as seen from the Earth and completeness is determined solely by the fraction of the orbit that resides within the solar elongation limit. Orbits away from 1 au gradually drift away from the anti-solar point and eventually exit the ``blind spot’’ caused by the solar elongation limit, allowing their detection. An important implication is that the gap in Fig 2 could contain undiscovered km-sized or larger asteroids which may be potentially hazardous (PHAs). To eliminate or significantly reduce the gap in a few decades or sooner, it would be necessary either to operate a survey with a much reduced solar elongation limit or move the detector away from the Earth.
Figure 3: Observational completeness for asteroids with semimajor axis within 0.01 au of Earth’s for a synthetic 40-year survey with a solar elongation cutoff of 70o and a limiting magnitude V=20.7. The asteroid parameters were H=14, e=0.1 and I=5o. Completeness takes values from 0 to 1 and is linearly proportional to greyscale intensity. The region of near-zero completeness centred at a = 1.000 au and Δλ = 180o is caused by the asteroid not exceeding the elongation cutoff for the duration of the survey.
At the meeting we will show model results to demonstrate how the observational completeness for co-orbital asteroids depends on the elements of the orbit: eccentricity, inclination, periapsis and node. An estimate for the number of as-yet-undiscovered co-orbital asteroids as a function of size will also be provided. In addition, we will be applying the simulator to known asteroids presently observed in different libration modes of the 1:1 resonance: Trojans (2010 TK7; Connors et al, 2011), horseshoes (419624 2010 SO16; Christou & Asher, 2011) and quasi-satellites (469219 Kamoʻoalewa; Chodas, 2016) and aim to report the results at the conference.
Acknowledgements: This work was supported via grant ST/R000573/1 from the UK Science and Technology Facilities Council (STFC).
References:
Chodas, P., 2016, The orbit and future motion of Earth quasi-satellite 2016 HO3, DPS meeting #48, id.311.04.
Christou, A. A., Asher, D. J., 2011, A long-lived horseshoe companion to the Earth, MNRAS, 414, 2965-2969.
Connors, M., Wiegert, P., Veillet, Ch., 2011, Earth’s Trojan asteroid, Nature, 475, 481-483.
Tricarico, P., 2017, The near-Earth asteroid population from two decades of observations, Icarus, 284, 416-423.
How to cite: Christou, A., Nedelchev, B., Borisov, G., Dell’Oro, A., and Cellino, A.: Earth's blind spot: A closer look at observational biases for Earth coorbital asteroids, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-92, https://doi.org/10.5194/epsc2021-92, 2021.
The knowledge of even some basic physical properties of a NEO such as the composition and the internal structure has strong implications for both science and impact mitigation. Depending on its composition and internal structure a meter-size object can completely burn in the atmosphere or reach the ground excavating an impact crater. To date, only 20% of the known NEO population has been characterized. The percentage rises 30% when considering only objects larger than 1 km. The reason is that physical characterization requires availability of large aperture telescopes, accurate ephemerides, and can be performed only if the object is sufficiently bright.
International efforts devoted to NEO physical characterization have undoubtedly succeeded in the last decade in addressing this problem through the organization of extensive observational campaigns within the framework of international cooperative programs. Yet the observational work and the associated modelling and simulation research is far from being exhausted in particular as far as the physical characterization of PHOs and smaller objects (D<140 m) passing close or colliding with the Earth are concerned.
The aim of the NEOROCKS project is to look at the 2020 horizon and beyond, by proposing an innovative approach that takes into consideration the incoming operations of the next generation sky surveys (with wide-field high-sensitivity telescopes), which will dramatically change the NEO discovery scenario.
The Project
NEOROCKS utilizes an innovative approach focused on:
- a) performing high-quality physical observations and related data reduction processes;
- b) investigating the strong relationship between the orbit determination of newly discovered objects and the quick execution of follow-up observations in order to face the threat posed by the “imminent impactors”;
- c) profiting of the European industrial expertise in on-going Space Situational Awareness initiatives to plan and execute breakthrough experiments foreseeing the remote tasking of highly automatized robotic telescopes, in order to provide a proof-of-concept rapid-response system;
- d) guarantee extremely high standards in the data dissemination through the involvement at agency level of a data center facility already operating in a European and international context.
The key issue, which marks the radical difference of this approach, is the early onset (from discovery) of a direct link between orbital and physical characterization. Our process continuously analyses the new published detections, in order to find out those which deserve attention as potentially hazardous. For each object identified, the astrometric follow-up and the associated orbit improvements are activated in closed loop until the accuracy of the ephemerides enables successful attempts of observations devoted to physical characterization. Speeding up this process, to complete it within the typical period of visibility of a newly discovered object in the vicinity of our planet (days to weeks), provides an innovative pre-operational scenario for addressing the “imminent impactors” threat. This is particularly relevant since small objects in route of collision with the Earth are likely to be routinely discovered by the new generation NEO sky surveys. Therefore, our approach aims to introduce an entirely new methodology into future operational NEO hazard monitoring systems.
The introduction of novel methods for orbit determination and for the prioritization of follow-up observations are at the core of our approach. To assess performances that it can reach, a real-time telescope tasking experiment is envisaged as a test case scenario with the potential to scale up to a global level.
Observation campaigns focussed on already known objects and the associated data reduction and analysis are also performed throughout the project, in order to provide high-quality data on specific interesting targets for science and mitigation. This goal is achieved thanks to the participation of astronomical institutions and observatories that can access top-class instrumentation (e.g. 3-10m aperture telescopes) and to perform challenging radar observations within the framework of international collaborations.
NEOROCKS also sets up necessary infrastructure to store, maintain and disseminate data produced and tools developed, well beyond the nominal lifetime of the project, thus granting the continuation of its approach and the update of its results. This is achieved through partnership with ASI Space Science Data Centre (SSDC https://www.ssdc.asi.it/), which is equipped with necessary HW/SW environment.
Team and activities
The main subject of NEOROCKS is to boost the NEO follow-up observations scenario devoted to determine the parameters characterizing asteroid properties, such as composition, shape, spin and mass: these quantities are relevant for our understanding of the nature of NEOs and the potential hazard they pose to human beings.
Another fundamental activity is focused in orbit determination and data management: special attention will be given to the timely detection and characterization of small potential imminent impactors of the Earth, which are likely to represent the next real threat.
Fig. 1 shows the Work Package Breakdown and Fig. 2 the Work Logic.
NEOROCKS has the potential to perpetuate the approach followed during the project and the results obtained, through the in-kind contribution of the ASI-SSDC in hosting the project products. The possibility of profiting from a well-established facility devoted to science data exploitation after the project is finished ensures a high-level dissemination toward the scientific and technological communities involved in NEO research as well as to the public at large.
The NEOROCKS team includes also industrial partnerships actively participating to European Space Awareness programmes. The goal of this activity is to probe the engagement of European and international partners in a proactive contribution to the detection of NEO potential threats, as well as to the planning and implementation of effective mitigation measures in a highly synergic and complementary scenario.
Acknowledgements. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870403.
How to cite: Dotto, E., Banaszkiewicz, M., Banchi, S., Barucci, M. A., Bernardi, F., Birlan, M., Carry, B., Cellino, A., De Léon, J., Lazzarin, M., Mazzotta Epifani, E., Mediavilla, A., Nomen Torres, J., Perna, D., Perozzi, E., Pravec, P., Snodgrass, C., and Teodorescu, C. and the NEOROCKS team: The EU Project NEOROCKS — NEO Rapid Observation, Characterization, and Key Simulations Project, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-389, https://doi.org/10.5194/epsc2021-389, 2021.
Introduction. The NEO Rapid Observation, Characterization and Key Simulations (NEOROCKS) project is funded (2020-2022) through the H2020 European Commission programme to improve our knowledge on near-Earth objects by connecting expertise in performing small body astronomical observations and the related modelling needed to derive their dynamical and physical properties. The Instituto de Astrofísica de Canarias (IAC), and in particular members of the Solar System Group, participate in the NEOROCKS project and currently lead one specific task: to collect observational data, mainly in the visible and near-infrared wavelength regions, of NEAs that have been observed in the past using the Arecibo Planetary Radar. In this work we present preliminary results, focusing on those targets having high signal-to-noise ratio radar data.
Observations. Our observations include spectroscopy, color photometry and lightcurves. They are performed using the facilities located at the Observatorios de Canarias (OOCC), that include the El Teide Observatory in the island of Tenerife and the El Roque de los Muchachos Observatory in the island of La Palma. Visible and near-infrared spectra are mainly obtained using the 10.4-m Gran Telescopio de Canarias (GTC) and its visible (OSIRIS) and near-infrared (EMIR) spectrographs. We also use the ALFOSC spectrograph at the 2.5-m Nordic Optical Telescope (NOT). Visible color photometry is obtained using the MuSCAT2 instrument at the 1.5-m Telescopio Carlos Sánchez (TCS). The setup allows to obtain simultaneous imaging in the g, r, i, and zsvisible bands. Time-series photometry in the visible is obtained using several telescopes, including the 46-cm TAR2, 80-cm IAC-80, and 1-m Jacobus Kapteyn Telescope (JKT).
Results. Spectra in the visible and/or the near-infrared wavelengths, as well as color photometry in the visible, are used to taxonomically classify the targets and to infer their composition (Fig 1). In the case of having no albedo measurements for one object, we can also use the taxonomy to have an estimation of the albedo based on the spectral class, and therefore determine the size of the asteroid. Lightcurves are used to both get the asteroid rotational period and, together with radar data, to obtain the shape and the spin axis orientation of the target (Fig. 2). In this way, a full characterization can be obtained for every asteroid observed within this program.
Acknowledgements. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870403.
How to cite: de León, J., Licandro, J., Popescu, M., Medeiros, H., Morate, D., Pinilla-Alonso, N., Perez-Toledo, F., and Planetary Radar Team*, A. and the NEOROCKS Team: NEOROCKS characterization programme of near-Earth asteroids previously observed with radar, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-221, https://doi.org/10.5194/epsc2021-221, 2021.
Introduction. The near-Earth object (NEO) population is composed of asteroids and comets that have orbits close to the Earth. This population is the most accesible vestige from the building blocks that formed the Solar System, for spacecrafts, and for detailed observations from ground-based facilities. The proximity of these objects give us advantages, but also risks. The NEO Rapid Observation, Characterization and Key Simulations (NEOROCKS) project has been recently funded (2020-2022) through the H2020 European Commission programme to improve the knowledge on NEOs by connecting expertise in performing small body astronomical observations and the related modelling needed to derive their dynamical and physical properties. The IAC, and in particular members of the Solar System Group, participate in the NEOROCKS project and are currently leading one specific task to do observations of NEOs in support of the Arecibo Planetary Radar Program, using the facilities located at the Observatorios de Canarias (OOCC) and managed by IAC. These observations include times-series photometry (light curves), visible to near-infrared spectroscopy, and color photometry. We are focusing in those targets observed in the past by the Arecibo telescope and which have high signal-to-noise (SNR) radar data. In this work we present the results obtained for asteroid (159402) 1999 AP10.
Observations. Our observations included spectroscopy and time-series photometry – over the visible wavelength. Spectroscopic data were obtained with the ALFOSC spectrograph at the 2.5-m Nordical Optical Telescope (NOT), located at the El Roque de Los Muchachos Observatory (La Palma). A solar analogue star was observed at the same airmass as that of the asteroid. Data reduction followed standard procedures and was done using IRAF tasks. The spectra were bias and flat-field corrected before extracted and collapsed to one dimension. We wavelength calibrated both the spectra of the asteroid and solar analogue using ThAr+Ne+He lamps. In a final step, we divided the spectrum of the asteroid by the spectrum of the solar analogue to obtain the asteroid reflectance. In the attempt to obtain the rotational properties as rotational period, spin direction and shape model for the asteroid (159402) 1999 AP10, we did light curve observations between 2020 and 2021 using the TAR2 at TAR (Remote Open Telescope, Telescopio Abierto Remoto) installation. This telescope is a robotic observatory with two 42 cm diameter Centurion telescopes (TAR1 and TAR2), equipped with high-sensitivity FLI-Kepler sCMOS cameras and located at Teide Observatory (Tenerife). The observations at TAR2 were performed using the clear filter. To process the photometric images and to obtain the magnitudes we used the Photometry Pipeline (PP) developed by Mommert (2017). We used the software MPO Canopus to obtain the rotational period from the light curves. For the determination of the photometric shape model, we used the programs described by the model from Kaasalainen and Torppa (2001) and Kaasalainen et al., (2001).
Results. In Fig. 1, we present the spectrum over the visible wavelengths of the asteroid (159402) 1999 AP10, it is normalized to unity at 0.55 μm (black points). We used the M4AST Tool (Popescu et al. 2012; http://spectre.imcce.fr/m4ast/index.php/index/home) to obtain a taxonomical classification of this object, finding that it best fits into the S-complex (DeMeo et al. 2009), i.e., it is composed mainly of silicates.
Figure 1: The spectrum of (159402) 1999 AP10 (black points). The spectral curve is normalized to unity at 0.55 μm. Using the M4AST we have the curve of the best fit in red lines from taxonomic classification of Sv-type.
Time-series photometry is a very efficient technique to obtain asteroid physical properties like rotation period, spin orientation, size, and shape. In the JPL webpage (https://ssd.jpl.nasa.gov/sbdb.cgi) the rotational period for the asteroid (159402) 1999 AP10 is 7.908 h. Using our light curves (with MPO Canopus), we obtain a rotational period of 7.9176 +/- 0.0152 h, and a light curve amplitude of 0.28 mag. The Fig.2 shows the light curves used to find the best fit and the rotational period. The obtained value for the period is in good agreement with the one listed at JPL.
Figure 2: Three light curves of the asteroid (159402) 1999 AP10 from January, 2021. We did the fit on MPO Canopus and we obtained the rotational period of 7.917 +/- 0.0152 h and a light curve amplitude of 0.28.
By obtaining rotational data from an asteroid at different viewing geometries allows to determine its photometric shape model (Kaasalainen and Torppa 2001; Kaasalainen et al. 2001). We observed the asteroid (159402) 1999 AP10 at several viewing geometries. Thus, we will present two preliminary photometric shape models, the first with only the data obtained by us and the second with our data plus data from the Asteroid Lightcurve Photometry Database.
References.
Mommert, M. PHOTOMETRYPIPELINE: An Automated Pipeline for Calibrated Photometry, Astronomy & Computing, 18, 47, 2017.
Kaasalainen, M., Torppa, J., Optimization Methods for Asteroid Lightcurve Inversion. I. Shape Determination, Icarus, 153, 24-36, 2001.
Kaasalainen, M., Torppa, J., Muinonen, K., Optimization Methods for Asteroid Lightcurve Inversion. II. The Complete Inverse Problem, Icarus, 153, 37-51, 2001.
Popescu, M., Biirlan M., Nedelcu D. A., Modeling of asteroid spectra - M4AST, Astronomy & Astrophysics, Volume 544, id.A130, 10 pp, 2012.
DeMeo, F. E., Binzel R. P., Silvan, S. M., Bus, S.J., An extension of the Bus asteroid taxonomy into the near-infrared, Icarus, 202, 160-180, 2009.
Acknowledgements. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870403.
How to cite: Medeiros, H., de León, J., Licandro, J., Popescu, M., and Pinilla-Alonso, N. and the Arecibo Planetary Radar Team* and NEOROCKS Team**: Physical characterization of near-Earth asteroid (159402) 1999 AP10 in support of the Arecibo Planetary Radar Program within the NEOROCKS project., Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-783, https://doi.org/10.5194/epsc2021-783, 2021.
- Introduction
The study of near-Earth objects (NEOs) is crucial to better understand the origin, formation and the evolution of the solar system. In particular, compositional, morphological and orbital characterisation of NEOs sheds light on the delivery of water and organics [1,2,3] to the prebiotic Earth, while ironically, some NEOs could be potential hazards for life on Earth [4], as it has been witnessed in the past during impacts. Furthermore, these objects are also of interest for the future of humankind, for they could be useful as vital resources during interplanetary travel. Given this context, we apply the G-mode multivariate statistical clustering method [5,6,7] on the orbital parameters of the currently available NEOs population, to probe potential associations with their spectral classification [8,9,10].
- Data and methods
We apply the G-Mode multivariate statistical clustering analysis to selected orbital elements of NEOs to determine any dynamical clustering of objects. Once the clusters of objects are found, we proceed to investigate whether they have any correlations with spectral classes. The G-mode method leads to an automatic statistical clustering of a sample containing N objects (NEOs in this case), described by M variables (orbital elements) with the only control imposed by the user being the confidence level q1, expressed in terms of σ.
Our sample consists of 10669 NEOs belonging to the dynamical groups Atiras, Atens, Apollos and Amors, available from the Minor Planet Center, filtered based on their orbital uncertainty (excluding those with an uncertainty parameter > 4). Our input parameters to the G-mode method are twofold. First, we use three variables: inclination (i), eccentricity (e) and semi-major axis (a) of the orbit as these are the main three parameters that define an orbit around the Sun. Secondly, we include three pseudo-parameters: mean orbital intersection distance with respect to the Earth (eMOID), perihelion distance (q) and aphelion distance (Q) of the orbit, in addition to the aforementioned three parameters, thus using six variables.
- Preliminary results
Using i, e and a of the NEOs in our sample as inputs for G-mode, we obtain three clusters of NEOs at q1=1.9σ (with an accurate classification probability of 94.26%). The mean parameter values of each cluster with the median absolute deviation are given in Table 1. We have also reported some other parameters of interest, which include, Tisserand parameter with respect to Jupiter (TJ) and the absolute magnitude H. At this criterion, the vast majority of objects are clustered in the cluster #1. The cluster #2 with only 20 objects, appears interesting, as it is constrained by low-inclined, quasi-circular Earth-like orbits. The objects of the final cluster #3 are constrained by their relatively larger inclinations.
We next used six variables: i, e, a, eMOID, q and Q as inputs for G-mode, while still holding q1 fixed at 1.9σ, in which case six clusters are found as reported in Table 2. Among the reported clusters, clusters #3,4 and 6 are of particular interest, for they could be associated with Jupiter-family cometary nuclei (2 < TJ < 3) as per their Tisserand parameter with respect to Jupiter. As such, the objects in these three clusters could potentially be extinct cometary nuclei. Interestingly, these clusters also have relatively higher eccentricities. We have checked available taxonomic classifications of NEOs [11,12,13] in the literature to get an insight into the composition of the objects found in our G-Mode clusters. Although taxonomic classifications are not available for the majority of members in the clusters, we find that (i) cluster #3 contains 4 C-type objects, (ii) cluster #4 contains 1 C-type, 2 D-type, 1 L-type, 5 S-type and 1 X-type objects, (iii) cluster #5 contains 1 B-type, 1 C-type, 1 T-type and 1 X-type objects. Apart from the S-type objects, the others usually have dark and red spectra indicative of primitive origin, which does not reject a cometary composition.
We will augment this on-going study with more data and final results will be presented and discussed.
- Acknowledgements
We acknowledge the financial support from Agenzia Spaziale Italiana (ASI, contract No. 2017-37-H.0 CUP F82F17000630005). We also acknowledge funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 870403.
References
[1] Marty, B., Guillaume, A. et al. 2016, Earth and Planetary Science Letters, Volume 441, Pages 91-102
[2] Altwegg, K, Balsiger, H, Bar-Nun, A. et al. 2015, Science, Vol. 347, Issue 6220, 1261952
[3] Ehrenfreund, P. & Sephton 2006, Faraday Discuss., The Royal Society of Chemistry, 133, 277-288
[4]Perna, D., Barucci M. A., Fulchignoni M. 2013, Astronomy and Astrophysics Review, Vol. 21,65
[5] Barucci, M.A., Capria, M.T., Coradini, A. et al. 1987, Icarus 72, 304
[6] Gavrishin, A. I., et al. 1992, Earth, Moon and Planets, 59, 141-152
[7] Barucci, M.A., Belskaya, I., Fulchignoni, M. et al. 2005, AJ 130, 1291
[8] Bus, S. J., & Binzel, R.P. 2002, Icarus 158, 146
[9] DeMeo, F. E., Binzel, R. P., Slivan, S. M. & Bus, S. J. 2009, Icarus, 202, 160-180
[10] DeMeo, F. E., Alexander, C. M. O., Walsh, K. J.et al. 2015, Asteroids IV, 13-41
[11] Perna, D., Barucci, M.A. et al. 2018, Planetary and Space Science, 157, 82-95
[12]Devogèle, M., Moskovitz, N. et al. 2019, The Astronomical Journal, American Astronomical Society, 158, 196
[13] Ieva, S., Dotto, E. et al. 2020, A&A, 644, A23
How to cite: Deshapriya, J. D. P., Perna, D., Bott, N., Hasselmann, P. H., Giunta, A., Dotto, E., Perozzi, E., Ieva, S., and Mazzotta Epifani, E.: Statistical clustering analysis of NEOs using their orbital parameters to find correlations with spectral classes, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-614, https://doi.org/10.5194/epsc2021-614, 2021.
1.Introduction
In recent decades, we have been observing an exponential increase in near-Earth asteroids(NEAs) discoveries especially smaller than 200m(VSAs). According to the Holsapple model and observational data[2], VSAs can rotate much faster than larger asteroids. The reason for this is the monolithic structure as opposed to the larger asteroids made of smaller stones, the so-called rubble pile. VSA holds together mainly due to cohesive forces, not gravity, so many of them have rotational periods shorter than the 2.2h spin limit typical of rubble piles.
However, we do not know much about these objects, especially in terms of their taxonomy, which may turn out to be the key to a better understanding of the composition of VSAs, thereby their threats, and a better determination of the rotation limit taking into account the taxonomic type. Only ~1\% of these bodies are assigned a taxonomic class[7].
2.VSA observation issues and methods
VSAs are faint, with a mid-class telescope(<=2m), they can only be observed during close approaches, when they move quickly on the celestial sphere. This makes observations difficult using the classical methods used for further objects.
In our photometric observation, the telescope follows the asteroid keeping the NEA image circular on CCD frame, but the star images extend into long trails. An example of such observations at extremely high speed NEA on the sky was presented at the last year's EPSC(see[4]). Luckily, there was a photometric night then and instrumental measurements were enough to determine the rotation period. In worse conditions and/or when we want to determine the colour indices, we need accurate differential photometry. For this purpose, we use a circular aperture for the asteroid image and a pill aperture[1] for comparison stars images. We raised the issue of the use of the pill aperture in NEA photometry in[5]. Solar analogs from the PanSTARRS catalog were used as comparison stars.
An appropriate observation strategy is essential in determining the color indices of newly discovered NEAs. We need to know the rotation period. Many VSAs are superfast rotators(P<2.2h), and our observations of new objects are adapted to effectively detect periods between almost the entire range at relatively high S/N.
The general idea is to make 10s exposures for 15min (detection period ~1-15min) followed by 60s exposures for 2h (detection period ~5-120min) and, depending on the observation time, repeat these observation blocks several times. Exposures in these blocks are made with wideband filters.
Between these blocks we make a sequence of B,L,V,L,R blocks - each with 60s exposures taken for 15-20min, where L is our broadband filter.
Then, by moving the B,V,R lightcurves to the most accurate L lightcurve, one can determine the magnitude shift in relation to the L lightcurve, obtaining L-B,L-V,L-R, hence we get B-V and V-R.
We noticed that in the case of rotation periods close to the time of colour exposures, we can assume that each measurement is averaged brightness over the period. Then we determined the brightness in a given filter from the arithmetic mean, and the uncertainty from the standard deviation of the mean. The same can be done when the exposure time is a multiple of the period.
To check the impact of the assumption of ideal averaging over period on the results, we run simulations. We assume that the synthetic composite lightcurve obtained from 10-second exposures is the ideal curve. We integrate this synthetic composite lightcurve over the period to get the brightness we would get if the exposure time were equal to the period. Then we integrate the part of the curve corresponding to the color exposure time and repeat this by slightly shifting the phase from which we start to integrate, until we return to the initial phase. In this way, we get all possible values that we can get at a given exposure time. Then we compare the mean result with the value obtained by the integration over the period.
3.Observation and results
We conducted our observations in search of super-fast rotating VSAs between October 2020 and April 2021. We were able to determine the physical properties of several objects. Most of the observations were made with the 0.7-m RBT/PST2 telescope at the Winer Observatory in Arizona. For 2021 DW1, we organized a larger campaign involving telescopes from around the world. We devoted a separate poster to this object at this conference[6].
Below are the results for 2020 UA, which we observed on 20th October 2020. More details and results for the remaining asteroids will be announced at the conference.
In Fig.1, we present the composite lightcurve for the best solution of the rotation period P=64.60+/-0.015s and amplitude 0.25mag. Since the time of colour exposures is 93% of the rotation period, we checked whether we can assume that P=texp for the determination of indices. It turned out that the impact was negligible, the average difference between the true average brightness period and our results is 0.0003+/-0.0047mag. The final indices are presented in Fig.2.
Fig.1.Composite lightcurve for 2020 UA. We used two 10-s exposure blocks during 15min each. The break between the blocks was 6.5h.
Fig.2.Colour-colour plot. The blue point is the result for 2020 UA(brightness in g,r,i obtained using PanSTARRS solar analogs), the uncertainty range is marked with a cross. Other symbols represent data for NEAs of various taxonomic types taken from[3].
References
[1]Fraser et al.(2016) AJ,151,151-158
[2]Holsapple(2007) Icarus,187,500-509
[3]Ivezic et al.(2001) AJ,122,2749-2784
[4]Koleńczuk et al. (2020) EPSC Abstracts,Vol.14,EPSC2020-809,https://doi.org/10.5194/epsc2020-809
[5]Koleńczuk, Proceedings of the Polish Astronomical Society,Vol.10,ISBN:978-83-950430-8-6,2020,101-104
[6]Kwiatkowski et al. Photometry and model of near-Earth asteroid 2021 DW1 from one apparition, EPSC 2021
[7]Perna et al.(2018) P&SS,157,82-95
How to cite: Koleńczuk, P. and Kwiatkowski, T.: Determination of colour indices of super-fast rotator near-Earth asteroids, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-758, https://doi.org/10.5194/epsc2021-758, 2021.
The near-Earth asteroid (3200) Phaethon is classified as an active asteroid and is one of the largest objects with a perihelion within the orbit of Mercury. A dust tail has been observed during each of the last 3 closest approaches with the Sun. The activity, which is likely not driven by volatile sublimation, strongly suggests that Phaethon is the most likely parent body of the annual Geminid meteor shower. Phaethon is the main target for the JAXA DESTINY+ mission that will measure the dust environment, among other goals.
Regolith properties in the near-surface of asteroid can be inferred from the thermal inertia, Γ = √kρc. The effective thermal conductivity, k, is the most influential controlling factor in thermal inertia, as opposed to heat capacity (c) and bulk density (ρ). The effective thermal conductivity can expressed as a sum of the radiative conductivity and solid conductivity, which are controlled by the grain size and porosity of the regolith: specifically, the conduction through contacts through the regolith grains and the radiative transfer within the pores between them. Gundlach and Blum (2013) presented a thermal conductivity model that accurately models both these effects for planetary regoliths.
Because the radiative component of conductivity is temperature dependent (T3) it implies that thermal inertia is also temperature dependent. By extension, the strong inverse dependence that temperature has on heliocentric distance means that thermal inertia will increase with decreasing heliocentric distance. Rozitis et al., (2018) calculated this dependence for 3 NEAs: (1036) Ganymed, (1580) Betulia, and (276049) 2002 CE26. They found a wide variation in the variability, with Ganymed showing a strong dependence and Betulia showing a weak dependence.
The thermal inertia of Phaethon was previously estimated to be 600 ± 200 J m-2 K-1 s-1/2 by Hanus et al. (2018) and 880+580-330 J m-2 K-1 s-1/2 by Masiero et al. (2019). While Hanus et al. (2018) used a convex shape model derived from lightcurve inversion techniques, Masiero et al. (2019) used assumed a spherical shape. Furthermore these two different thermal inertia estimates were derived using two distinct datatsets: thermal emission spectrum from Spitzer and photometric data from IRAS and UKIRT Green et al (1995) was used by Hanus et al. (2018) and 5 epochs of WISE/NEOWISE photometry was used by Masiero et al. (2019). Both of these works alos reported diameter estimates of Phaethon (~5.1 and ~4.6 km) that are noticeably smaller than the reported effective diameter from delay-Doppler radar observations (5.5 - 6 km; Taylor et al. 2017).
Using a radar-derived shape model and thermal infrared observations from 10 observing epochs, we estimate Phaethon's thermal inertia for each epoch. We independently derive an effective diameter of ~5.5-5.6 km that is consistent with the radar observations and find that Phaethon's thermal inertia increases with decreasing heliocentric distance. Using the regolith thermal conductivity model presented by Gundlach and Blum (2013), we model the thermal inertia as a function of heliocentric distance for various grain sizes and porosities (Figure 1). We find that larger grain sizes are consistent with smaller heliocentric distances and smaller grain sizes are consistent with larger heliocentric distances.
Figure 1. Phaethon's thermal inertia as a function of heliocentric distance (black points) and modeled thermal inertia for different regoolith grain sizes and porosities.
We consider two other possibilities for Phaethon's regolith: 1) a depth-dependent layered model and 2) a two component latitude-dependnt model. The layered model consists of a fine-grained regolith covering solid bedrock and the two component model consists of two distinct grain sizes for each of Phaethon's northern and southern hemispheres. The effective thermal inertia of the layered regolith model exhibits a stronger dependence on heliocentric distance, as expected, but does not fit the observed thermal inertia estimates well. On the other hand, the model that consisters distinct grain sizes is very consistent with Phaethon's observed thermal inertia. We conclude that Phaethon's northern hemisphere consists of larger regolith grains compared to its southern hemisphere.
How to cite: MacLennan, E., Marshall, S., and Granvik, M.: Evidence for Regolith Heterogeneity on (3200) Phaethon, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-804, https://doi.org/10.5194/epsc2021-804, 2021.
Introduction
Planetary surfaces not protected by dense atmospheres suffered by many impacts by asteroids and comets, leaving craters as a reminders of it. Among all craters observed on surfaces of Earth, Mars, Moon, and Venus, about 3-4% are binary craters. It is believed they formed by the simultaneous impacts of the two components of binary asteroid systems.
Binary asteroids represent 15% of near-Earth asteroids, apparently at odd with the rate of binary craters on planetary surfaces. Miljkovic et al. showed with 3-D hydrocode simulations that only a fraction of impacts by binary asteroids create distinguishable binary craters, solving the apparent discrepancy with the fraction of binary craters of 3-4%. However, the few binary crater examples in have striking properties: nearly similar size and North-South orientation, unexpected from a population of binary asteroids displaying a typical size ratio of 0.3 and with a mutual orbit closely aligned with the ecliptic.
Survey and simulations
A large fraction of impact craters on Mars exhibits thick and continuous ejecta blanket emplaced in a pyroclastic flow-like regime due to the presence of volatile material at the moment of the impact. This facilitates the recognition of synchronous impact events, making the surface of Mars an ideal case to survey for the existence of binary craters and infer the binary asteroids properties.
Our study focuses on craters more than 4km in diameter located between latitudes 50°N and 50°S compiled in the database and recently revised by A. Lagain in 2021. We chose this minimum diameter to remove potential bias that could be caused by isolated secondary impacts and this range of latitude to avoid high-latitudes resurfacing processes. Binary craters are recognized based on the morphology of their cavity or their ejecta blanket.
The presence of a septum (i.e. a linear contact perpendicular to the direction of both crater centers on their shared rim or ejecta blanket), is one of the main morphological characteristics allowing to identify them, as illustrated on Fig.1. We classify candidates binary craters following Miljkovic scheme: Elliptical, Peanut, Doublet, Tear drop, Overlapping and Circular. We will not analyze the last category as it represents craters whose a binary asteroid impact origin is more uncertain.
In parallel, we conduct three-body dynamical simulations to predict the orientation or binary craters on Mars surface as inferred from the known population of binary asteroids, extending the previous work by Melosh and Stansberry.
Results and Conclusions
Out of the 31,778 craters we inspected, we identify 28 doublet, 44 peanut, 17 overlapping, 23 tear, and 13 elliptical craters. Using crater scaling laws adapted for Mars impact condition, the size of impactors having formed those craters range between approximately 100 m and 5 km. 28 doublet craters indicate on largely separated binary asteroids with more than 10 diameters of the primary asteroid size.
The observed distribution of orientation angle θ of doublet craters as well as the simulated one are presented in Fig.2. It is clearly seen that the distributions are different. We also performed a Kolmogorov-Smirnov test on the two distributions and we can reject with a 99.99% confidence that the two distributions are similar.
Our numerical simulations show that neither the separation nor the orientation of the binary asteroid components is affected by tidal forces of Mars. It means that there is an unobserved population of widely separated binaries, whose mutual orbits is not coplanar with their heliocentric orbits. These binary systems are very difficult to be detected by typical lightcurve programs but our results reveal the existence of these systems.
How to cite: Vavilov, D., Carry, B., Lagain, A., Guimpier, A., Conway, S., Devillepoix, H., and Bouley, S.: Unknown population of binary asteroids, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-316, https://doi.org/10.5194/epsc2021-316, 2021.
Introduction
The identification of binary systems among the near-Earth asteroids (NEAs) has grown considerably in recent years, mainly due to detections made by radar observations and to the increase in the number of photometric lightcurves. It is estimated that about 15% of the NEAs population large than 0.3 km are to be binaries, while other 15% can be contact binaries (Pravec et al. 2006; Margot et al. 2015). Most of these binaries consist of one larger primary component and a small secondary component (or satellite), with the primaries having almost spherical shapes and fast rotations. On the other hand, less than 1% of the binary asteroids discovered among the NEA population have components of almost equal size, such as (69230) Hermes, (190166) 2005 UP156, 1994 CJ1 and 2017 YE5. Here, we report a complete physical characterization of the 2017 YE5 system.
Observations and data reduction
Photometric lightcurve observations of the nearly equal-mass binary near-Earth asteroid 2017 YE5 were carried out at the Observatório Astronômico do Sertão de Itaparica (OASI, Brazil) and the Blue Mountains Observatory (BMO, Australia) between July and August 2018. Additionally, using the Observatorio Astronómico Nacional de San Pedro Mártir (OAN-SPM, Mexico), we observed 2017 YE5 system using photometry with four different broadband filters (BVRI Johnson-Cousins filters) to obtain its photometric spectrum and color indices. Data reduction was performed using the MaxIm DL software following the standard procedures of flat-field correction and sky subtraction. To generate the lightcurves, we obtained the reduced magnitude, i.e., the corrected magnitude to a unity distance by applying -5 log(rΔ) to the observed magnitudes with r and Δ being, respectively, the asteroid's distances from the Sun and from the Earth in AU. To investigate binary periods we used the "Dual Period Search" tool in MPO Canopus software which is based on the method described by Pravec and collaborators (Pravec et al. 2006). To obtain the color indices and the photometric spectrum of 2017 YE5, we used standard field stars to calculate the zero-point of the night and, consequently, the calibrated magnitude of the asteroid. Thus, the photometric spectrum was derived from the observed color indices minus the solar color indices and transfomed to normalized reflectance at the V filter.
Results
We found that 2017 YE5 system has a mutual orbital period of Porb = 23.7 ± 0.01 h and a secondary short period of P2 = 14.88 ± 0.02 h, indicating a possible asynchronous component or non-principal axis rotator in this system (Monteiro et al., submitted). These results are in good agreement with those reported by radar observations (Taylor et al. 2018, 2019). Our result for the orbital period of the binary system is shown in the Figure below. We derived the mean density of 2017 YE5 is from 0.6 to 1.2 g/cm3, implying a rubble-pile internal structure for the components.
We found that the color indices determined for 2017 YE5 from OAN-SPM data indicate a very red surface, falling among the D-type asteroids and JFCs in the color-color diagram (V-R vs. V-I) shown in the Figure below. This is in line with the high spectral slope observed in the photometric spectrum of 2017 YE5, which was classified as D-type (Monteiro et al., submitted).
Infrared data obtained at the NASA's IRTF, made available by the MIT-Hawaii Near-Earth Object Survey (MITHNEOS), exhibited a thermal emission in the 2.5 μm range for which we adjusted a low albedo of 2-4% by applying a thermal model (Rivkin et al. 2005). Figure below shows the original infrared spectrum of 2017 YE5 displaying a thermal emission at long wavelengths in the 2.5 μm range and also shows the corrected spectrum after removal of the thermal tail. In addition, we classified the thermally corrected spectrum of 2017 YE5 as a D-type asteroid in the Bus-DeMeo taxonomy. All results presented in this section were recently submitted (Monteiro et al., submitted).
Conclusions
Our physical characterization of this binary system sheds light on its physical properties, including rotational and orbital period, albedo and taxonomic type. We suggest that 2017 YE5 has a cometary origin, due to its comet-like albedo and orbit (TJ = 2.87). It is important to mention that, while suggesting that 2017 YE5 is a dormant Jupiter-family binary comet, we do not reject that it came from the outer main-belt.
Acknowledgements
F.M. thanks the financial support given by FAPERJ (E-26/201.877/2020). E.R., M.S., M.C. and P.A. would like to thank CAPES and CNPq (Brazilian funding agencies) for supporting this work through diverse fellowships. Support by CNPq (305409/2016-6) and FAPERJ (E-26/202.841/2017) is acknowledged by D.L. The authors are grateful to the IMPACTON team and, in particular, to R. Souza and A. Santiago for the technical support, and the OAN-SPM team. The authors are also grateful to Andy Rivkin for help with the correction of spectrum for thermal excess in order to constrain the albedo.
References
Harris A. W., et al., 1989, Icarus, 77, 171
Margot J.-L., Pravec P., Taylor P., Carry B., Jacobson S., 2015, in Michel P., DeMeo F. E., Bottke W. F., eds, Asteroids IV. Pp 355–374
Pravec P., et al., 2006, icarus, 181, 63
Rivkin A. S., Binzel R. P., Bus S. J., 2005, Icarus, 175, 175
Taylor P. A., et al., 2018, in AAS/Division for Planetary Sciences Meeting Abstracts #50. p. 508.07
Taylor P. A., et al., 2019, in Lunar and Planetary Science Conference. Lunar and Planetary Science Conference. p. 2945
How to cite: Monteiro, F., Rondón, E., Lazzaro, D., Oey, J., Evangelista-Santana, M., Arcoverde, P., De Cicco, M., Silva-Cabrera, J. S., and Rodrigues, T.: Physical characterization of equal-mass binary near-Earth asteroid 2017 YE5: a possible dormant Jupiter-family comet, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-400, https://doi.org/10.5194/epsc2021-400, 2021.
Due to their proximity Near-Earth objects (NEOs) provide us with a unique opportunity to investigate asteroids with diameters down to dozens of meters. Moreover, NEOs create a constant potential hazard to the Earth, and thus the study of their physical properties is crucial for estimating the potential risks. A new photometric survey was carried out in the framework of the NEOROCKS (NEO Rapid Observation, Characterization, and Key Simulations) project funded by the European Union’s Horizon 2020 program with the aim to derive the visible colors of NEOs and perform the initial taxonomic classification.
The photometric survey was performed with a use of a 1.2m telescope at the Haute-Provence observatory and a 1.0m telescope at the Pic du Midi observatory, both located in France. Standard broadband Johnson-Cousins and Sloan photometric systems were used.
Color indexes were measured for a total of 51 NEOs. Among them, 24 objects belong to a group of potentially hazardous asteroids (PHAs). The majority of objects have absolute magnitude H in a 17-20 mag range.
The preliminary taxonomy was done following the classification by [1] using M4AST service [2]. In order to have better statistics only the main taxons S-, C-, and X-complexes, and A-, D-, V-types were considered. Fig. 1 shows color-color diagrams for the observed NEOs. One can see that different classes of objects are concentrated in the different areas of the plots, which suggests that our taxonomic classification is rather reliable. Additionally, our taxonomic classification was confirmed by albedo values that are available for about a third of objects in our sample. About 43% of objects in our sample belong to the S+Q-complex, about 19% to X-complex, 16% to C-complex, 12% were classified as D-types, and, finally, 6% and 4% as A- and V-types, respectively. The found distribution is in a general agreement with the previous works (e.g. [3, 4, 5]).
Fig. 1. Color-color diagrams for the objects in our survey showing their classification into the main taxonomic classes. The boxes represent the 1σ deviation from the mean colors for the groups of “carbonaceous” and “silicate” objects.
The median values of absolute magnitudes and estimated diameters vary for different groups of objects in our sample: H=18.10±0.95 and D=1219±729 m for low-albedo "carbonaceous" objects, whereas H=19.50±1.20 and D=344±226 m for "silicate" objects. This could be a result of an observational bias towards higher albedo objects. The absolute magnitude versus Minimal Orbital Intersection Distance (MOID) was also derived (Fig. 2). PHAs by almost 65% represented by “silicate” objects, however there are also a few low albedo objects that could be more challenging in terms of mitigation that relies on the porosity of the object (e.g. [6]).
Fig. 2. Earth’s MOID vs. absolute magnitude for different groups of NEOs. The line at MOID=0.05 au separates PHAs from the rest of the NEOs.
Acknowledgements. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870403.
References
[1] DeMeo, F., Binzel, R., Stephen M. Slivan, S., Bus, S. Icarus, 202, 160, 2009.
[2] Popescu, M., Birlan, M., Nedelcu, D. A&A, 544, 130, 2012.
[3] Binzel, R. P., DeMeo, F. E., Turtelboom, E. V., et al. Icarus, 324, 41, 2019.
[4] Devogèle, M., Moskovitz, N., Thirouin, A., et al. AJ, 158, 196, 2019.
[5] Ieva, S., Dotto, E., Mazzotta Epifani, E., et al. A&A, 644, A23, 2020.
[6] Perna, D., Barucci, M. A., Fulchignoni, M. The Astronomy and Astrophysics Review, 21, 65, 2013.
How to cite: Hromakina, T., Birlan, M., Barucci, M. A., Fulchignoni, M., Colas, F., Fornasier, S., Merlin, F., Sonka, A., Petrescu, E., Perna, D., and Dotto, E. and the NEOROCKS team: NEOROCKS project: results from photometric survey of Near-Earth objects, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-114, https://doi.org/10.5194/epsc2021-114, 2021.
The near-Earth asteroids (NEAs) represent excellent scientific opportunities to study the dynamical and physical properties of small bodies of the Solar System. Moreover, the celestial bodies with sizes lower than one km can be studied using a variety of techniques, thanks to the fact that they come close to Earth orbit.
We report the preliminary results of an ongoing observational program for obtaining the visible color indexes of NEAs. Our survey use the MuSCAT2 instrument [1] mounted on the 1.52 m Telescopio Carlos Sánchez located at Teide Observatory (Canary Islands, Spain). The setup allows us to obtain simultaneous imaging in the g (400–550nm), r (550–700 nm), i( 700–820 nm), and zs (820–920nm) bands. The visible colors have proven to be efficient to broadly differentiate between the major compositional groups [2]. Thus, by using MuSCAT2 instrument we can obtain the spectro-photometric classification for a large number of NEOs. The simultaneous imaging allows to study the relation between the rotational properties and the taxonomic type. It can also reveal possible heterogeneous compositions of the observed targets.
Fig. 1 The absolute magnitude distribution of NEAs observed with TCS – MuSCAT2 instrument
The program started in March 2018 with one or two observing nights allocated on every month. A total of 267 spectro-photometric observational sets were collected. They correspond to 198 NEAs with the absolute magnitudes distributed in the range of 12 -24 mag (Fig. 1). Our schedule gave priority to the targets observed by radar, to potentially hazardous asteroids and to those suitable for a space mission. We also considered the newly discovered objects. Most of these are very small objects (in general smaller than 300m) and the opportunities to study them are rare.
Fig. 2 The color-color diagrams of objects with known visible colors and spectral classification, used as training sets in the K-Nearest Neighbors algorithm.
We used the Photometry Pipeline (PP) software [3] and several Python scripts for reducing the data. We applied the K-Nearest Neighbors (KNN) algorithm to obtain the spectro-photometric classification. For the training set we used the 86 asteroids for which spectral data is also available and the taxonomic type is known ([4], [5]). We grouped the taxonomic classes in seven groups, namely Q-type and S-complex (similar to silicate asteroids), V-type (specific to basaltic objects), A-type (an olivine-dominated composition), B/C-complex (similar to carbonaceous meteorites), X-complex and D-type (reddish surfaces – possible cometary nature). The color-color diagrams of this sample used for training is shown in Fig. 2. The classification results are shown in Fig. 3.
Fig 3. The taxonomic distribution of the observed sample
By assigning a probability for each classification we quantified the effect of color errors. This was derived by applying a Monte-Carlo approach. We generated 10000 simulated values for each of the colors of an asteroid by using a normal distribution where the mean is the observed color and the standard deviation is the color error. The KNN classifier was applied for each of these colors. The reported class is the one predicted in most cases and the probability is the occurrence rate.
Acknowledgments
MP, JL, JdL, and DM acknowledge support from the ESA P3NEOI and NEOROCKS projects. The work of MP, GNS, and RMG was supported by a grant of the Romanian National Authority for Scientific Research – UEFISCDI, project number PN-III-P1-1.1-TE-2019-1504. This work was developed in the framework of EURONEAR collaboration.
References
[1] Narita, Norio et al.; Journal of Astronomical Telescopes, Instruments, and Systems, Volume 5, id. 015001 (2019).
[2] Parker, A.; Icarus, Volume 198, Issue 1, p. 138-155 (2008).
[3] Mommert, Michael; Astronomy and Computing, Volume 18, p. 47-53 (2017).
[4] Popescu, M et al.; Astronomy & Astrophysics, Volume 627, id.A124, 21 pp (2019).
[5] Binzel R. P., et al. 2019, Icarus, 324, 41
How to cite: Popescu, M., de León, J., Licandro, J., Nicolae Simion, G., Morate, D., Văduvescu, O., Luis Rizos, J., Medeiros, H., and Mihai Gherase, R.: Simultaneous observations in four optical bands of near-Earth asteroids using TCS/MuSCAT2 instrument, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-820, https://doi.org/10.5194/epsc2021-820, 2021.
INTRODUCTION
The Asteroid Terrestrial Last-impact Alert System (ATLAS) currently consists of two robotic telescopes in Hawaii. Together they scan the entire visible night sky every two nights in wideband orange and cyan filters down to ~19.5 mag. In addition to rapid discovery and follow up of Near-Earth Objects, ATLAS serendipitously observes a large number of asteroids and other moving objects. Since operations began in 2015 ATLAS has collected a substantial photometric database of ~7x107 observations for ~430,000 asteroids.
Asteroids are valuable compositional and dynamical tracers that can be used to constrain the processes of Solar System evolution. The observed size distribution of an asteroid population can inform us of its primordial formation and subsequent collisional evolution. Composition of a population can indicate a common origin; such as a protoplanetary disk formation region or a relation through asteroid collisional families. We aim to utilise the ATLAS database to investigate the physical properties of a large number of asteroids, by fitting phase curve models to the photometric observations.
The form of the phase curve depends on the physical properties of the asteroid and is parameterised by a variety of models which are each described by absolute magnitude and slope parameters. Absolute magnitude, H, is related to the size and albedo of the body. The form of the phase curve is determined by the slope parameter in the phase function and depends on the surface composition and structure. Hence these parameters may be used as proxies for the properties of asteroids when more detailed information is unavailable.
METHODS
An analysis of an earlier dataset has been performed using MCMC techniques by Mahlke et al. (2021), providing phase curves in the H, G1, G2 and H, G12* systems (Muinonen et al. 2010, Penttilä et al. 2016). In this work we fit both these systems plus the original H, G system (Bowell et al., 1989) to all asteroids in the ATLAS dataset, using Levenberg-Marquardt least squares fitting. We perform a separate fit in both the o and c ATLAS filters. We have investigated various methods of outlier rejection, and use techniques such as initial data cuts, iterative sigma clipping, and avoidance of low galactic latitudes. These have considerably improved the quality of the dataset. However, in some cases the photometric observations may not be well described by the phase curve model due to physical phenomena such as large amplitude rotational variation, or changing aspect angle for asteroids with high spin obliquities.
We have created a dataset of phase curve parameters for ~370,000 asteroids, and identify a subset of high quality phase curves where the phase curve model describes the data well and absolute magnitude and slope have low formal uncertainties. We analyse in detail the distribution of these phase curve parameters and verify them with comparison to previous work and catalogue values.
RESULTS
In general we find good agreement between our phase curve results and previously published studies, especially for well observed bright asteroids. We identify metrics that indicate the ability to obtain a good fit to the phase function, such as number of observations and phase angle coverage. Furthermore, we demonstrate the scientific value of our database by comparing the properties of the leading and trailing Jupiter Trojans observed with ATLAS.
The ability to determine phase curves for large numbers of asteroids, and studying the statistics of their properties, highlights the potential value of sparse photometric survey data for asteroid science. This is especially relevant to the upcoming Legacy Survey of Space and Time (LSST) which will perform photometry of asteroids at a similar cadence to ATLAS.
FIGURES
Figure 1. The semimajor axis distribution of asteroids in the ATLAS database between 1.5 and 5.5 AU. ATLAS samples a wide range of populations; including the main belt, Hildas and Jupiter Trojans.
Figure 2. The distribution of detections for asteroids observed by ATLAS in the o and c filters.
Figure 3. Proper orbital elements (semimajor axis versus inclination) of selected asteroids from our database of phase curve fits. Asteroid families appear as distinct clusters with similar surface scattering properties as measured by the phase curve parameter G12*.
ACKNOWLEDGEMENTS
This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. ATLAS is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory (SAAO), and the Millennium Institute of Astrophysics (MAS), Chile.
JR acknowledges the support of STFC Consolidated Grant ST/P000304/1.
REFERENCES
Bowell, E., Hapke, B., Domingue, D., et al. 1989, in Asteroids II, ed. R. P. Binzel, T. Gehrels, & M. S. Matthews, 524–556
Mahlke, M., Carry, B., & Denneau, L. 2021, Icarus, 354, 114094, doi: 10.1016/j.icarus.2020.114094
Muinonen, K., Belskaya, I. N., Cellino, A., et al. 2010, Icarus, 209, 542, doi: 10.1016/j.icarus.2010.04.003
Penttilä, A., Shevchenko, V. G., Wilkman, O., & Muinonen, K. 2016, Planet. Space Sci., 123, 117, doi: 10.1016/j.pss.2015.08.010
How to cite: Robinson, J. E., Fitzsimmons, A., Young, D. R., Denneau, L., Heinze, A., Tonry, J., and Bannister, M.: Asteroid Phase Curves with ATLAS: Requirements for Sparse Survey Observations, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-706, https://doi.org/10.5194/epsc2021-706, 2021.
The asteroids’ brightness is not generally constant, but presents time variations that depend on the asteroid shape, albedo, rotation period, and other factors. In 1901, Von Oppolzer first noted changes in the brightness of (433) Eros (von Oppolzer 1901), and the first correct period for this asteroid was published in Bailey & Pickering (1913). Today, lightcurves, time-series data for brightness variations, are available for more than 10,000 asteroids, and periods are known for more than 8,300 bodies (Warner et al. 2009). Data from asteroid lightcurves can be used, through lightcurve inversion methods, to infer information on the asteroid shapes, rotation periods, and spin axis directions. The Database of Asteroid Models from Inversion Techniques (DAMIT, (Durech et al. 2010)) currently has models for 3303 asteroids. Asteroid photometric lightcurves in a “FITS-like”, self-describing, style are publicly available for several bodies at the Asteroid Lightcurve Data Exchange Format (ALCDEF), website (http://alcdef.org (Stephens & Warner 2018; Warner et al. 2011; Stephens et al. 2010)).
Asteroid lightcurves data are, in essence, a time series, and, as such, may be considered part of the discipline that Griffin et al. (2012) call “time-domain astronomy”. In statistical literature, dominant methods for studying time series are time-domain parametric modelling. Popular introductory (Brockwell & Davis 2016) and graduate-level (Shumway & Stoffer 2017) textbooks mostly focus on auto-regressive time-domain models, with only brief mentions of Fourier frequency-domain methods. Yet, while the latter methods have been used for several decades to study asteroid lightcurves and obtain asteroid periods (see for instance Lenz & Breger (2005); Szabó et al. (2016) and references therein), auto-regressive models, like the ARIMA methods, have not received as much attention. ARIMA stands for Auto-regressive (AR), integrated (I), moving average (MA). The AR part indicates that the variable of interest is regressed on its own lagged values. The MA indicates that the regression error is a linear combination of error terms that occurred at present and various past times. The I means that the variable values have been replaced by differences in their values and the previous ones.
In this work, we attempt to use ARIMA methods to model observed lightcurves of main-belt asteroids, as available at the ALCDEF database. The ideal lightcurve shape would display “smooth, double-waved, quasi-sinusoidal” form Cellino et al. (1989). This kind of perfect shape is, however, very rare. Some features deforming the lightcurve are very common, and, for the same asteroid, can be caused by changes of the aspect angle, the angle between the asteroid spin axis and the direction of observation of the body from Earth, at different observing epochs. Cellino et al. (1989) introduced four categories for classifying irregularities in the shape of lightcurves:
(i) Irregular morphology of one or more extrema
(ii) Different levels of the extrema
(iii) Different time intervals between the extrema
(iv) More or less than two maxima or minima per cycle
More recently, Harris et al. (2014) identified cases of very complex lightcurves with six maxima, for asteroids (5404) Uemura and 2010 RC130, which were later also retrieved by Szabó et al. (2016) for the asteroids (29628) 1998 TX30 and (37201) 2000WS94 observed during the K2 Kepler space telescope mission. For this work, we will define three categories of lightcurves:
(i) Regular lightcurves, with no prominent irregularities as defined by Cellino et al. (1989). Examples of asteroids with these kinds of lightcurves in the ALCDEF database are (8) Flora, (16) Psyche, and (593) Titania.
(ii) Complex lightcurves, with at least one shape irregularity. Examples are (21) Lutetia, (39) Laetitia, and (43) Ariadne.
(iii) Very complex lightcurves, as defined by Harris et al. (2014). Examples are (5404) Uemura and (37201) 2000WS94.
Figure (1) displays the ARIMA best-fits for (43) Ariadne and (5404) Uemura. ARIMA models were able to fit even very complex lightcurves with six maxima, like those of (5404) Uemura and (37201) 2000 WS94. Most models obtained in this work achieved a precision, measured in terms of mean relative error, of less than 1%, and future forecast of lightcurve data on timescales of a few hours is possible for most studied asteroids.
Article submitted to MNRAS. This is publication from the MASB (Machine Learning applied to Small bodies https://valeriocarruba.github.io/Site-MASB/) research group.
References
Bailey, S. I. and Pickering, E. C. (1913). Observations of Eros and other asteroids. Annals of Harvard College Observatory, 72(5):165–189.
Brockwell, P. J. and Davis, R. A. (2016). Introduction to Time Series and Forecasting. Springer, New York City, NY, USA.
Cellino, A., Zappala, V., and Farinella, P. (1989). Asteroid shapes and lightcurve morphology. ICARUS, 78(2): 298–310.
Durech, J., Sidorin, V., and Kaasalainen, M. (2010). DAMIT: a database of asteroid models. A&A, 513:A46.
Griffin, E., Hanisch, R., and Seaman, R., editors (2012). New Horizons in Time Domain Astronomy (IAU S285), volume 285 of 285.
Harris, A. W., Pravec, P., Galád, A., Skiff, B. A., Warner, B. D., Világi, J., Gajdoš, Š., Carbognani, A., Hornoch, K., Kušnirák, P., Cooney, W. R., Gross, J., Terrell, D., Higgins, D., Bowell, E., and Koehn, B. W. (2014). On the maximum amplitude of harmonics of an asteroid lightcurve. ICARUS, 235:55–59.
Lenz, P. and Breger, M. (2005). Period04 User Guide. Communications in Asteroseismology, 146:53–136.
Shumway, R. H. and Stoffer, D. S. (2017). Time Series Analysis and Its Applications with R Examples. Springer, New York City, NY, USA.
Stephens, R. and Warner, B. D. (2018). The ALCDEF Database and the NASA SBN/PDS: The Perfect Merger. In AAS/Division for Planetary Sciences Meeting Abstracts #50, volume 50 of AAS/Division for Planetary Sciences Meeting Abstracts, page 417.03.
Stephens, R. D., Warner, B. D., and Harris, A. W. (2010). A Proposed Standard For Reporting Asteroid Lightcurve Data. In AAS/Division for Planetary Sciences Meeting Abstracts #42, volume 42 of AAS/Division for Planetary Sciences Meeting Abstracts, page 39.14.
Szabó, R., Pál, A., Sárneczky, K., Szabó, G. M., Molnár, L., Kiss, L. L., Hanyecz, O., Plachy, E., and Kiss, C. (2016). Uninterrupted optical light curves of main-belt asteroids from the K2 mission. A&A, 596:A40.
von Oppolzer, E. (1901). Notiz betr. Planet (433) Eros. Astronomische Nachrichten, 154(14):297.
How to cite: Carruba, V. and Aljbaae, S.: Predicting asteroid lightcurves using ARIMA models, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-36, https://doi.org/10.5194/epsc2021-36, 2021.