Introduction: Ryugu is a second-generation C-type asteroid formed by the reassembly of fragments of a previous larger body in the main belt. While the majority of Ryugu samples returned by Hayabusa2 are composed of a lithology dominated by aqueously altered minerals, clasts of a more pristine olivine-pyroxene lithology remain in the least-altered samples [1]. These clasts are objects of prime interest for revealing the composition of the original building blocks of Ryugu’s parent asteroid and of the dust from which they formed.

We used infrared hyperspectral imaging to analyze four mm-sized sections of Ryugu samples extracted from Chamber A (A0026) and Chamber C (C0002, C0023, C0025). We compare the Ryugu IR spectra to observations of asteroids, comets, meteorites and interplanetary dust particles (IDPs), to study the potential links between the original building blocks of Ryugu’s parent asteroid and objects that retained dust from the outer Solar System.

Methods: We used different FTIR microscopes at the SMIS beamline of synchrotron SOLEIL [2]: (1) a synchrotron-radiation-fed microscope equipped with a large mid-IR range MCT/B-detector, (2) a far-IR bolometer-equipped microscope, (3) an imaging microscope equipped with a 128×128 pixels focal plane array detector. For (1) and (2), different apertures were used from 5 to 100 µm. For (3), we used a field of view of ~420 µm and pixel size of 3.3 µm, and several IR tiles were accumulated in mosaic IR hyperspectral images, to analyze mm-sized areas in Ryugu stones. Complementary point-to-point micro-IR measurements were performed at Tohoku University (globar source), with spots of ~100-200 µm.

Results and discussion: While a large fraction of the matrix of C0002 shows the 10-µm feature of phyllosilicates similar to aqueously altered chondrites, very different silicate spectral features are observed at some clasts detected by Nakamura et al. [1], because of the presence of anhydrous inclusions. Most of these inclusions have a double-peak structure, due to the intimate mixture of hydrated and anhydrous silicates, in particular olivine with a band at ~880 cm^-1 (11.36 µm). Some of them show the signature of pure olivine, while others show a strong spectral contribution of pyroxene at ~1075 cm^-1 (9.3 µm). A very few grains have a large spectral profile indicating a significant contribution of amorphous phases. Several olivine grains are also observed in C0023 and C0025, in the less-altered lithologies. These features are absent from A0026.

In a principal component analysis, spectra of Ryugu samples, CI chondrites and hydrated IDPs reveal a pattern that correlates with increasing alteration, from the least altered clasts of Ryugu stones, to weakly altered Ryugu clasts, and then major (most altered) lithology of Ryugu, Alais, Tagish-Lake, Orgueil, and the hydrated IDPs.

Some grains enriched in amorphous silicates discovered in C0002 have IR spectra similar to D-type asteroid Hektor (a Jupiter Trojan) [3], to comet Hale-Bopp [4], and to anhydrous chondritic porous IDPs of cometary origin [5]. They can be identified with anhydrous grains rich in GEMS (Glass with Embedded Metal and Sulfides) [1], which in turn are similar in texture and composition to the GEMS found in IDPs of probably cometary origin, formed in the protoplanetary disk.

Conclusions: The amorphous-rich grains in C0002 are one of the most interesting reservoirs of anhydrous “cometary-like” dust found in Ryugu. Their IR spectra suggest a possible link between at least one of the reservoirs from which Ryugu’s parent asteroid originated and the reservoir that formed comets and D-type asteroids in the outer protoplanetary disk [6].

Acknowledgments: This work is part of the multi-analytical sequence of the Hayabusa2 “Stone” MIN-PET group, led by T. Nakamura. It was supported by the Centre National d’Etudes Spatiales (CNES-France, Hayabusa2 mission) and by the ANR project LARCAS (Grant ANR-22-CE49-0009-01) of the French Agence Nationale de la Recherche. The micro-spectroscopy measurements were supported by grants from Region Ile-de-France (DIM-ACAV) and SOLEIL.

References: [1] Nakamura T. et al. (2022). Science doi:10.1126/science.abn8671. [2] Rubino S. et al. (2023). Earth, Planets and Space 75. doi:10.1186/s40623-022-01762-8. [3] Emery J.P. et al. (2006). Icarus, 182, 496–512. [4] Crovisier J. et al. (1997) Science, 275, 1904. [5] Brunetto R. et al. (2011). Icarus, 212, 896–910. [6] Brunetto R. et al. (2023). ApJL, 951:L33. doi:10.3847/2041-8213/acdf5c.

How to cite: Brunetto, R., Nakamura, T., Lantz, C., Fukuda, Y., Aléon-Toppani, A., and Dionnet, Z. and the Hayabusa2 Stone team: IR spectra of Ryugu's anhydrous ingredients compared with primitive dust from the outer solar system, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-58, https://doi.org/10.5194/epsc2024-58, 2024.

Carbonate minerals are tracers of the chemical and temporal evolution of aqueous alteration on the parent bodies of meteorites, in particular of the hydrated CI and CM carbonaceous chondrites. While principal differences in the carbonate abundances of CI and CM chondrites representative of  different alteration scenarios are well established [1, 2], detailed timelines concerning e.g. the variability in the composition of the alteration fluid and the physical conditions on the parent bodies during alteration remain open questions and require further investigations.

The samples of (162173) Ryugu returned by the JAXA Hayabusa2 mission show similarities with CI chondrites [3, 4]. Thanks to the MicrOmega instrument in the Extraterrestrial Curation Center in Sagamihara, Japan [5, 6], Loizeau et al. [7] identified areas enriched in carbonates in more than 180 Ryugu grains, showing that, consistent with CI chondrites, dolomite-like and breunnerite-like are the most abundant, while the relative abundance between the two depends on the size of the carbonate inclusion. Fujiya et al. [8] reported the presence of rare and small calcite grains in Ryugu, in combination with anhydrous silicates (olivine and Mg-rich pyroxene), indicating that less aqueous alteration occurred in these regions. Using O and C isotopes, they conclude that calcites precipitated first among the carbonates. Yamaguchi et al. [9] further report oscillatory zoning of Mn, Fe, and Ca in dolomites, indicating varying fluid compositions during carbonate formations.

The hyperspectral microscope MicrOmega is in the unique position of analysing the entire returned material of Ryugu under a controlled N₂-purged environment within the ISAS, JAXA, curation facility. This enables us to perform a large-scale, statistical description of mineral distributions in the sample. MicrOmega obtains spectra from 1-3.6μm in a 256x256 pixel grid with a spatial pixel scale of 22.5μm. We present here the distribution of carbonates in over 50% of the Ryugu sample in terms of mass, with a focus on small-scale variability (tens of microns, refer to Fig. 1) within carbonates. A particular emphasis is placed on the identification of calcites, given their established link to pristine lithologies in CI chondrites and on Ryugu [2, 8]. Our results show that carbonates follow different compositional distributions between the two  chambers A and C, the former representing Ryugu surface material and the latter material excavated via an impactor. We explore different hypotheses concerning the origin of this discrepancy in the chambers' carbonates.

Fig. 1: Top: False-RGB images of carbonate-rich regions on grains C0181 and A0360, colour-coded by the best-matching carbonate references. C0181 is rich in breunnerite-like inclusions, while carbonates in A0360 are predominantly  dolomite-like. Carbonates in C0181 show indications of Fe-zoning from the interior to the exterior regions of the inclusion. Bottom: The average spectrum of the breunnerite-like (left) and dolomite-like (left) pixel in C0181 and A0360 respectively (solid lines), together with the best-matching reference spectrum (faded line). N gives the number of pixel matched to the respective best-matching reference spectra.

A more recent addition to the collection of pristine asteroidal material on Earth are the samples of (101955) Bennu collected by NASA’s OSIRIS-REx mission and returned in September 2023. While initially suspected to be of CM-like composition [10], the analysis of bulk major and trace elements suggests that Bennu consists of CI-like material [11]. Unlike for Ryugu, remote-sensing data indicates the presence of large-scale carbonate veins on Bennu’s surface, showing relative species-abundances typical for CM chondrites, with calcite, dolomite, and magnesite as predominant carbonates [12]. At small scales on the returned sample, several carbonate species (e.g. dolomite, calcite, and breunnerite) have been identified [13]. We conclude with an outlook on MicrOmega’'s analyses of Bennu samples, scheduled for delivery by NASA to JAXA in August 2024. This delivery presents an excellent opportunity to compare Bennu and Ryugu samples using a consistent instrumental and experimental setup at ISAS, laying the groundwork for a direct comparison of Ryugu and Bennu in the near future.

References:
[1] Lee, M. R. et al. (2014) Geochim. Cosmochim., 144, 126-156.
[2] Endreß, M. and Bischoff, A. (1996) Geochim. Cosmochim., 60, 489-507.
[3] Yokoyama T. et al. (2023), Science 379, 786.
[4] Nakamura, T. et al. (2023), Science 379, 8671
[5] Bibring, J.-P. et al. (2017), Astrobiology, 17, 621-626.
[6] Pilorget, C. et al. (2022), Nature Astronomy, 6, 221-225
[7] Loizeau, D. et al. (2023), Nature Astronomy, 7, 391–397
[8] Fujiya, W. et al. (2023), Nature Geoscience, 8, 675-782
[9] Yamaguchi, A. et al. (2023), Nature Astronomy, 4, 398-405
[10] Hamilton, V. E. et al. (2019) Nat. Astron. 3, 332-340.
[11] Koefoed, P. et al. (2024), LPSC2024,
[12] Kaplan H. H. et al. (2020) Science, 370.
[13] Thomas-Keprta, K. et al. (2024), LPSC2024

How to cite: Mahlke, M., Lantz, C., Pilorget, C., Bibring, J.-P., Aléon-Toppani, A., Baklouti, D., Brunetto, R., Hatakeda, K., Jiang, T., Loizeau, D., Okada, T., Yada, T., and Yogata, K.: Aqueous alteration of Ryugu's parent body: Insights from carbonates seen by MicrOmega, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-174, https://doi.org/10.5194/epsc2024-174, 2024.

In December 2020, the Hayabusa2/JAXA mission returned to Earth ~5.4g of primitive material from the carbonaceous asteroid (162173) Ryugu. Since their return, the samples are stored and analysed in the ISAS (Institute of Space and Astronautical Science) Curation Facility. All the analyses in the Curation Facility are conducted under clean and controlled environment [Yada et al., 2023]. The measurements in the Curation Facility offer the opportunity to characterise the physical and chemical properties of Ryugu samples without any bias from the terrestrial atmosphere.

A systematic non-destructive characterisation of bulk samples and individual grains (a few mm in size) have been performed by the near-infrared (0.99 – 3.65 µm) hyperspectral microscope MicrOmega in the Curation Facility [Bibring et al., 2017, Riu et al., 2022]. To be specific, MicrOmega is able to characterise the feature around 2.7 µm, associated with the O-H stretching vibration in phyllosilicates. This absorption band has been detected at the surface of Ryugu by the NIRS3 spectrometer [Kitazato et al., 2019], and was also observed by MicrOmega at cm-scale, in the bulk samples [Pilorget et al., 2022]. With a spatial resolution of 22.5 x 22.5 µm² and a total field of view of ~ 5.7 x 5.7 mm², MicrOmega enables a study of the variations of spectral features at small scales. For example, variations in the depth and the position of the ~2.7 µm feature have been detected between the average spectra of ~200 mm-sized grains [Le Pivert-Jolivet et al., 2023]. In this study, we aim at characterising the spatial variations of the O-H feature at the surface of the grains. To study the feature at sub-mm scales, we averaged groups of 8x8 pixels at the surface of 233 individual mm-sized grains. We used different spectral parameters to estimate the position and the depth of the ~2.7 µm feature.

At sub-mm scales, we detect heterogeneities in the peak position and depth of the ~2.7 µm feature. In most cases, the spectral heterogeneities observed are at small scales (~200 µm). However, out of the 233 mm-sized grains characterised in this study, we observed large-scale heterogeneities on ~30 of them (some detections are to be confirmed). On these grains, the variations of the spectral parameters are consistent on several contiguous pixels (i.e. areas sizes ranging from several hundreds of microns to ~1.5 mm) and are observed at different illumination angles of the grains. The large-scale spectral heterogeneities exhibit variations in peak position, in band depth, or in both parameters. In some cases, the large-scale spectral heterogeneities are spatially correlated with a variation in the surface aspect of the grain or the reflectance level. For all grains, we observe variations of the degree of heterogeneity of the peak position from one grain to another. Grains with average peak position at lower wavelengths tend to have more homogeneous peak positions (i.e., the peak position varies little at the surface) and have stronger values of band depth than the grains with average peak position at higher wavelengths.

Previous work has shown that some Ryugu grains exhibit various sub-mm (<500 µm) lithologies with different degrees of aqueous alteration [Nakamura et al., 2022]. The next step of this work is to investigate whether our results could be partly related to these lithologies, or if the variation in heterogeneity degree and large-scale dichotomies reflects other physical or chemical processes. For example, a variation in the abundance of opaque phases could also affect the spectral parameters.

References:

Yada, T. et al., 2023, Earth, Planets and Space. 75, 170; Bibring, J.-P., et al., 2017, Space Sci. Rev. 208, 401-412; Riu, L. et al., 2022, Rev. Sci. Instrum. 93, 054503 ;Kitazato, K. et al., 2019, Science. 364, 272-275; Pilorget, C. et al., 2022, Nature Astronomy, 6, 221-225; Le Pivert-Jolivet, T. et al., 2023, Nature Astronomy, 7, 1445-1453; Nakamura, T. et al., 2022, Science, 379, 6634

How to cite: Le Pivert-Jolivet, T., Riu, L., Brunetto, R., Pilorget, C., Baklouti, D., Bibring, J.-P., Nakato, A., Lantz, C., Hamm, V., Hatakeda, K., Loizeau, D., Yogata, K., Poulet, F., Aléon-Toppani, A., Carter, J., Langevin, Y., Okada, T., Yada, T., and Usui, T.: Spectral variations of the 2.7 µm feature at sub-mm scales in Ryugu samples, within the ISAS Curation Facility, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-526, https://doi.org/10.5194/epsc2024-526, 2024.

Introduction:  The JAXA’s Hayabusa2 mission [1] rendezvoused with the Ryugu near Earth, C-type asteroid from June 2018 to November 2019, performing two touchdown operations with related sampling, as well as an artificial impact experiment.

Hayabusa2 studied the Ryugu’s morphology and color by means of the Optical Navigation Camera (ONC [2]) and studied its composition through spectra provided by the Near InfraRed Spectrometer (NIRS3 [3]). The mission revealed that Ryugu is one of the darkest object explored so far, given its geometric albedo of 0.043 [4].

In this work, we studied the average photometric properties of Ryugu and of the artificial impact crater area, defined between 4.5-10°N latitudes and 299-305°E longitudes by means of the ONC images. Then, we compared the phase functions with other asteroids explored by space missions, as well as with results obtained on Ryugu by applying different approaches [5] and in different spectral ranges [6].

Data and methods: We selected all images acquired in the mission stages close to the artificial impact event (occurred on 5^th April 2019), i.e., CRA-1, SCI and CRA-2: These images were collected from March to April 2019 at phase angles between 15° and 40°. In particular, we considered images provided by the ONC’s v band, centred at 0.55 mm.

The Ryugu’s average phase function was retrieved by applying an empirical method (e.g. [7-8], based on a statistical analysis and consisting of the following steps: 1) retrieval of the equigonal albedo (i.e., topography-corrected) by applying the Akimov disk function [9]; 2) retrieval of the median equigonal albedo at each phase angle; 3) retrieval of phase function; 4) comparison with disk-resolved phase functions of other asteroids, based on R20 (i.e., radiance factor at 20° phase angle) and PCS₁₅₄₀(i.e., phase function steepness between 15° and 40° phase angles).

The same procedure is then applied to a restricted dataset, including only the images covering the artificial impact area, acquired before and after the impact, respectively.

Results and discussion: The Ryugu’s average equigonal albedo’s phase function is shown in Figure 1.

Figure 1: Ryugu’s phase function.

This phase function is very similar (i.e., within two times the uncertainty) to that obtained from NIRS3 data [6], i.e., in the near-infrared range. This reflects the similar Ryugu’s optical properties in the two spectral intervals.

Figure 2 shows the PCS₁₅₄₀ vs R20 scatterplot for all disk-resolved phase functions of asteroids explored by space missions.

Figure 2. Steepness of phase function as a function of radiance factor at 20° phase for asteroids explored by space missions. Diamonds indicate C-type asteroids, crosses S-type asteroids, triangles X-type asteroids, asterisks V-type asteroids and squares E-type asteroids.

In Figure 2, asteroids belonging to the same taxonomic class are grouped together. Two exceptions arise: the Vesta dark regions, since they are a mixture of achondrites and carbonaceous chondrites, and Ryugu.

In order to verify the reliability of our result, we calculated the Ryugu’s PCS₁₅₄₀ on other phase functions obtained with different approaches on Ryugu’s ONC data [5]. A good agreement is found with the [5]’s disk-resolved phase function, while the disk-integrated Ryugu’s phase function shows a different PCS₁₅₄₀, more similar to other C-type asteroids.

We infer that the increasing spatial resolution results in a phase function flattening, due to reducing role of shadowing. A similar behaviour was observed on other dark asteroids, e.g., Ceres [7] and Bennu [10].

The artificial impact area’s phase function is found to be constant within errors between before and after the impact, suggesting similar photometric properties between surface and subsurface. Nevertheless, this could be due to the very narrow phase angle interval covering this area (having a 10° width), therefore a larger dataset is required to confirm this result.

Conclusions and future perspectives: We found that Ryugu’s visible and near infrared phase functions are similar within uncertainties, in agreement with the similar albedo in the two ranges.

While the Ryugu’s disk-integrated phase function is similar to other C-type asteroids, its disk-resolved phase function is flatter, due to the better spatial resolution of ONC images.

No phase function variation is observed after the impact event, but this could be due to the small dataset considered.

Acknowledgements: We thank the ONC development and operations Team.

This work is funded by Italian Space Agency through the ASI-INAF Agreement 2022-12-HH.0

References:

[1] Tachibana, S. (2021), In: Sample Return Missions: The Last Frontieer of Solar System Exploration, ed. A. Longobardo (Amsterdam: Elsevier)

[2] Kameda, S. et al. (2017), Space Science Reviews, 208, 17.

[3] Iwata, T. et al. (2017), Space Science Reviews, 208, 317.

[4] Sugita, S. et al. (2019), Science, 364, eaaw0422

[5] Tatsumi, E. et al. (2020), A&A, 639, A83

[6] Longobardo, A. et al. (2022), A&A, 666, A185

[7] Longobardo, A. et al. (2019), Icarus, 320, 97

[8] Longobardo, A. et al. (2014), Icarus, 240, 20

[9] Shkuratov, Y.G. et al. (1999), Icarus, 141, 132

[10] Golish, D. et al. (2021), Icarus, 357, 113724

How to cite: Longobardo, A., Angrisani, M., Palomba, E., Dirri, F., Yokota, Y., Kouyama, T., Amodio, A., and Olivieri, A.: Photometric properties of Ryugu and its artificial impact crater, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-749, https://doi.org/10.5194/epsc2024-749, 2024.

Introduction: The planned NASA-ESA Mars Sample Return (MSR) Campaign is a multi-mission effort intended to bring scientifically selected samples of Mars rock cores, regolith, and atmosphere to Earth for the purpose of scientific investigation and discovery. The Mars 2020 Perseverance Rover is collecting a stunningly diverse set of samples for potential return. and the planning for the missions to retrieve and deliver the samples is underway.

The currently envisaged high containment facility to which the samples would initially be delivered is referred to as the Sample Receiving Facility (SRF). It is strongly preferred to do as many measurements on the samples as possible in existing laboratories outside of containment for reasons including scientific quality and cost, but certain measurements will be needed to be made within the SRF. Sample investigations within the SRF would need to be carried out in support of the following three elements:

Initial Sample Characterization: required to plan properly for the optimized use of the samples for curation, safety, and scientific purposes (for a recent summary, see [1]);

Safety Assessment: implement a protocol derived from the Sample Safety Assessment Framework [2];

Science Investigations: support time-sensitive [3] and sterilization-sensitive [4] investigations that cannot be done using sterilized samples outside of high containment.

To minimize the footprint, cost, and complexity of the SRF in handling the samples from Mars, it is crucial to define properly the minimum set of investigations, measurements, instrumentation, and operations concept required to cover the initial characterization, safety assessment, and science investigation needs.

NASA and ESA appointed the international Measurement Definition Team Phase 1 (MDT-1). While the overall process of the MDT is similar to traditional Science Definition Teams (SDTs), the scope of this MDT is distinct because they must focus on the specifics of the measurement implementation plan, as well measurements needed for sample characterization and planetary protection. 

MDT-1 Statement of Task: The MDT was asked to perform four tasks (Figure 1):

• Overarching Investigation Strategy​: Determine options and priorities for activities inside and outside the SRF, providing a narrative rationale for the scientific basis underpinning the proposed investigations. ​
• Measurement Traceability Matrices​: Develop traceability matrices flowing from objectives to investigations to measurements and required capabilities within the SRF.​
• Reference Instruments: Provide descriptions of proposed suites of instruments capable of collecting the needed measurements, as well as interface requirements and any special accommodation considerations.​
• Concept of Operations (ConOps)​: Describe a feasible model concept of operations for activities to be conducted within the SRF that will maximize overall science return.

Figure 1. Generalized flow chart of MDT-1 Tasks.

MDT Composition: The MDT-1 committee consists of twenty competitively selected members of the international science community, co-chaired by Heather Graham and Chris Herd, an executive team consisting of Project Science representatives, and six ex-officio members representing NASA and ESA curation, the Centre for Disease Control (CDC), and liaisons with the Sample Safety Assessment Protocol Tiger Team (SSAP-TT).

MDT Process and Status: The essential deliverables of MDT are achieved via the sequential flow of Tasks 1-4 (Fig. 1), the starting point for which is a baseline set of science objectives. At a high-level, there are four proposed science objectives of Mars Sample Return, each of which are elaborated to form a total set of 17 proposed sub-objectives. These were formulated by the MSR Campaign Science Group (MCSG) [5], by adapting and building on proposed objectives laid out by numerous prior studies (e.g. [6]).

Since September 2023, MDT has first elaborated each of the 17 sub-objectives into specific research questions (Task 1), which were used to define specific measurements that can address them (Task 2).

A key step in MDT’s workflow has been to establish and apply logic to determine whether a measurement would need to be done inside the SRF. The model conceived produces a minimum set of measurements to be done in the SRF such that the scientific integrity of samples is preserved, and thus science objectives may be addressed.

Figure 2. Logic for determining whether a measurement must be done within the SRF (i.e. within biocontainment).

Measurements determined necessary to be in the SRF were then grouped and linked to the corresponding set of reference instruments and complemented with additional information, including measurement performance requirements, sample preparation needs, instrument accommodation considerations and sample mass requirements. With the resulting dataset, fully backward traceable to measurements, investigations and science objectives, Task 4 (ConOps) was addressed.

Two aspects required specific treatment in MDTs work plan: 1. Work by the SSAP-TT resulted in measurement requirements that are incorporated into MDT’s traceability matrix. Members of SSAP-TT and MDT-1 worked closely together to ensure that accurate and complete information was incorporated into measurement traceability. 2. Measurements necessary for initial sample characterization (e.g. box in Fig. 2) were established via a dedicated analysis of what sample properties must be known to properly allocate sub-samples for all the scientific investigations. 

Disclaimer: The decision to implement Mars Sample Return will not be finalized until NASA’s completion of the National Environmental Policy Act (NEPA) process.  This document is being made available for informational purposes only.

References

[1] Tait, K. T. et al. (2022). Preliminary Planning for Mars Sample Return (MSR) Curation Activities in a Sample Receiving Facility (SRF). Astrobiology, 22(S1), S-57-S-80. https://doi.org/10.1089/ast.2021.0105

[2] Kminek, G. et al., (2022). COSPAR Sample Safety Assessment Framework (SSAF). Astrobiology, 22(S1), S186–S216. https://doi.org/10.1089/ast.2022.0017

[3] Tosca, N. J. et al., (2022). Time-Sensitive Aspects of Mars Sample Return (MSR) Science. Astrobiology, 22(S1), S-81-S-111. https://doi.org/10.1089/ast.2021.0115

[4] Velbel, M. A. et al. (2022). Planning Implications Related to Sterilization-Sensitive Science Investigations Associated with Mars Sample Return (MSR). Astrobiology, 22(S1), S112–S164. https://doi.org/10.1089/ast.2021.0113

[5] MSR Campaign Science Group (MCSG) (2024). Mars Sample Return Campaign Science Objectives for the MSR Sample Receiving Project., 10^th International Conference on Mars, Pasadena CA, USA.

[6] Beaty, D. W. et al., (2019). The potential science and engineering value of samples delivered to Earth by Mars sample return: International MSR Objectives and Samples Team (iMOST). Meteoritics and Planetary Science, 54(S1), S3–S152. https://doi.org/10.1111/maps.13242

How to cite: Sefton-Nash, E., Carrier, B. L., Graham, H. V., Haltigin, T., Herd, C. D. K., Paardekooper, D., and Viotti, M.: Mars Sample Return (MSR) Sample Receiving Project (SRP) Measurement Definition Team (MDT-1): Overview and Status, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1142, https://doi.org/10.5194/epsc2024-1142, 2024.

Introduction: Now, the China National Space Administration has proposed an asteroid mission, Tianwen-2, which plans to return a sample of a sub-hundred-meter Earth quasi-satellite (469219) 2016 HO₃ Kamoʻoalewa. Early studies suggested Kamoʻoalewa originated from the Moon. However, here, we will report that Kamoʻoalewa is a space-weathering (SW)-matured LL-chondrite-like object.

Results: We first determined the composition of Kamoʻoalewa by comparing Kamoʻoalewa’s reflectance spectrum (which was previously reported by [1]) with that of meteorites. As a result, Kamoʻoalewa shows an absorption center at 0.984 µm, only falling into the range of LL-chondrites. (Fig. 1), suggesting that Kamoʻoalewa resembles LL chondrites in composition rather than other meteorite types.

Then we used an orbital dynamical calculation method [2] to trace the source region of Kamoʻoalewa. As a result, Kamoʻoalewa shows a probability of 72 ± 5% originating from the ν6 secular resonance. Given that Flora family adjacent to the ν6 secular resonance has been known as the major source region of LL-chondrite-like NEAs, such a high probability, therefore, emphasizes the possibility that Kamoʻoalewa is an LL-chondrite-like asteroid.

Particularly, Kamoʻoalewa shows an extremely red spectral slope (0.726, calculated within 0.45-2.194 µm) when compare with NEAs and main belt asteroids (MBAs), implying that Kamoʻoalewa is a strongly space-weathered asteroid. Our nanosecond laser irradiation experiment on LL5/6 chondrite Kheneg Ljouâd’s powder has successfully produced a slightly redder spectrum than Kamoʻoalewa (Fig. 2), proving that Kamoʻoalewa’s extremely red-sloped spectrum can indeed be contributed by SW processes. Furthermore, employing the radiative transfer mixing model [3-4], our calculation suggests that 0.29 ± 0.05 wt.% SMFe⁰ (sub-microphase metallic iron, a major SW product that darkens and reddens silicate asteroids) in Kamoʻoalewa’s regolith is required. This is higher than the average content of SMFe⁰ in the regolith of Itokawa (~ 0.2 wt.% [5]), suggesting that Kamoʻoalewa is indeed a SW-matured object. This is also consistent with our taxonomy of Kamoʻoalewa as S-type rather than Sq- or Q-type.

We also noted that Kamoʻoalewa’s spectrum is redder than the mean spectrum of its source region Flora family (which has an exposure age of 0.5-1 × 10⁹ year). Given that the SW rate at 1 AU area is about 10 times that of the main belt area, Kamoʻoalewa’s SW timescale is hence estimated as at least 0.5-1 × 10⁸ year. This exceeds the timescale of rapid reddening by solar wind irradiation (10⁶ yr [6]) and the average dynamical lifetimes of NEAs (10⁶ year [7]), indicating that Kamoʻoalewa broke as a fragment in the inner main belt very early and still retains most of the previous (non-near-Earth-space) SW information without significant later surface refreshing.

We also estimated Kamoʻoalewa’s rotation period as ~27 min (meaning that it is a single rock), size as 69.45 m × 58.49 m × 51.78 m, and its regolith size on 75.38 % of surface area was lower than 2 cm, suggesting that fine-sized grains dominate Kamoʻoalewa’s surface. Meanwhile, when we assumed Kamoʻoalewa has been accelerated to current rotation period with a uniform angular acceleration within the Flora family, the estimation suggests that YORP spin-up lifetime is 4.23 × 10⁴ to 4.23 × 10⁵ yr. It means that the loss of large-sized grains (fresher) may have started very early and significant accumulation of small-sized grains/dust (maturer) has continued over a very long time (10⁷ to 10⁸ yr).

Discussion: We explain that Kamoʻoalewa’s extremely red spectrum can be comprehensively contributed by long-term SW and weak resurface process: (1) long-term loss of young large-sized grains and the accumulation of mature small-sized materials, (2) small size of Kamoʻoalewa decreases the likelihood of surface refreshing caused by impact, (3) non-rubble pile structure may effectively avoid surface rejuvenation that would be driven by the inside-out movement of materials driven by spin-up and matter mixing driven by meteoroid impact, (4) Kamoʻoalewa did not underwent resurfacing by Earth encounters, because its minimum Earth orbit intersection distance (0.0345 AU) and perihelion (0.898 AU) is much larger than the range of Earth encounters (5-16 times Earth radius [8]), and quasi-satellites generally do not experience flybys with Earth as close as those observed for other co-orbital types.

We further predict that sub-hundred-meter, rapidly spinning silicate-rich NEAs with small perihelion may generally exhibit redder spectral slopes and SW matured surfaces. This is different from the current observation that the “Q-type/S-type” ratio increases with decreasing perihelion distance [9-10].

Fig. 1 Comparison of band I center and band area ratio (Band II/Band I) of Kamoʻoalewa with meteorites, the band I center of Kamoʻoalewa (0.984 µm) best matches to LL chondrites.

Fig. 2 Comparison of spectra of Kamoʻoalewa with fresh (blue line) and laser irradiated (red line) LL5/6 chondrite Kheneg Ljouâd. After irradiation, Kheneg Ljouâd’s spectrum significantly steeps and slightly steeper than Kamoʻoalewa, suggesting that Kamoʻoalewa-like extremely red spectra can indeed be contributed by long-term SW process

Reference: [1] Sharkey et al. (2021) Commun Earth Environ, 2, 1-7. [2] Granvik and Brown (2018) Icarus, 311, 271-287. [3] Lawrence et al. (2007) JGR: Planets, 112. [4] Lucey et al. (2011) Icarus, 212, 451-462. [5] Binzel et al. (2001) Meteorit Planet Sci, 36, 1167-1172. [6] Vernazza et al. (2009) Nature, 458, 993-995. [7] Nesvorný et al. (2017) AJ, 155, 42. [8] Nesvorný et al. (2010) Icarus, 209, 510-519. [9] Binzel et al. (2019) Icarus, 324, 41-76. [10] Demeo et al. (2023) Icarus, 389, 115264. [11] Demeo et al. (2009) Icarus, 202, 160-180.

How to cite: Zhang, P., Li, Y., Zhang, G., Yan, X., Zhang, Y., Vernazza, P., Cloutis, E., Hiroi, T., Granvik, M., Zhang, X., and Lin, Y.: (469219) Kamo'oalewa, A Space-Weathering-Matured LL-chondrite-like Small NEA: Target of the Tianwen-2 Sample Return Mission, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1281, https://doi.org/10.5194/epsc2024-1281, 2024.

Introduction:  A mission to (99942) Apophis would provide a unique opportunity to collect and return a regolith sample from a Near-Earth asteroid (NEA) as it passes very close to Earth [1,2].  ESA is currently investigating the possibility of an orbiter, as part of the RAMSES mission study, to fly close to (99942) Apophis before it makes its closest approach to Earth on Friday 13 April 2029, with the aim of observing the tidal and magnetospheric effects on the NEA during this close flyby [3]. Later, the asteroid will be well observed by the OSIRIS-APEX (or OSIRIS-REx Extended Mission to Asteroid Apophis) mission [4]. 
At present, none of these missions or mission studies are investigating the possibility of sample return with a very short duration sample return leg, requiring only a tiny additional momentum to return to Earth. We present the results of the concurrent engineering (CE) study on the feasibility of a sample return capsule based on "now-term technology" available from the space industry and the necessary mechanical, electrical and software interfaces based on the experience gained from previous small asteroid projects [5]. 

Overview of envisaged mission scenario baseline for APOSSUM - APOhiS SUrface saMpler: The Sample Return Probe or minisatellite should be launched as part of the RAMSES mission and be compatible with its mission requirements. We assume that RAMSES will rendezvous with asteroid (99942) Apophis in mid-February 2029. APOSSUM will be detached, land with partly autonomous navigation guidance, actively controlled by thrusters, sample the regolith, depart in mid-March 2029 and be guided towards Earth at a speed of a few tens of metres per second relative to the asteroid. This is orders of magnitude less than the speed required by previous sample-return missions because of the very close Earth flyby of (99942) Apophis on 13 April 2029. The spacecraft will cover the distance to Earth in about one month and arrive as the asteroid passes at a safe distance. The spacecraft's entry velocity is about 12.6 km/s, compared to the asteroid's 7.4 km/s fly-by, due to Earth's gravitational field. By entering the atmosphere in phase with the Earth's rotation, the entry velocity can be slightly reduced.

Design approach for Concurrent Engineering (CE) study :  The development follows a tailored concurrent engineering approach that considers the compressed timeline until the envisaged launch window of RAMSES. The selected subsystems must be available as "now-term technology", similar to “off-the-shelf" components. The entry capsule and the sampler are mission-specific developments.     

Brief sketch of storyline for CE study:  The envisaged operations are illustrated in the Operations Sketch: After launch, communication during cruise and near (99942) Apophis is via RAMSES (high bandwidth). Direct communication to Earth will be accomplished via the RAMSES satellite. APOSSUM approaches and scouts Apophis earlier. The initial mapping/reconnaissance phase identifies possible sampling targets. Asteroid approaches begin from a home position (≈5 km altitude) under ground control, similar to Hayabusa2. Tracking of features for final approach begins from ≈1 km down, for a simple mark-and-go "contrast seeker" with horizon tracking. In the final automatic approach, this effectively locks APOSSUM to Apophis‘ slow rotation at about 5 - 10 cm/s. A toroidal rotary brush is spun up before touchdown for sampling during an inertia- and thruster-supported touch-and-go ground contact. A reversible shutter is closed on bounce-back to prevent samples from drifting out again. A lift-off burn ensures APOSSUM clears the surface; later it is accelerated to near-escape velocity towards the parking position. A rehearsal and multiple sampling attempts can be performed. Return to Earth is achieved by the departure burn and successive correction burns into the re-entry corridor, with low-bandwidth communications and ranging with Earth.

APOSSUM System Design:  The spacecraft is designed around the selected entry capsule design. All other subsystems are attached and integrated. The attitude and orbit control systems are based on flight-proven cameras, sensors and propulsion units. An integrated core avionics approach using a mix of scalable on-board computers and communication equipment with off-the-shelf units such as antennae is envisaged, with new designs only where gap-fillers are needed. The outer shell of the structure provides space for thermal control and photovoltaics. 

References: [1] Binzel, Richard, et al.  Bulletin of the AAS 53.4 (2021). [2] Wagner, Sam, and Bong Wie.  Acta Astronautica 90.1 (2013): 72-79. [3] Kueppers, Michael, et al.  AAS/Division for Planetary Sciences Meeting Abstracts. Vol. 55. No. 8. 2023. [4] DellaGiustina, Daniella N., et al.  The Planetary Science Journal 4.10 (2023): 198. [5] Grimm, Christian D., et al.  Progress in Aerospace Sciences 104 (2019): 20-39. 

How to cite: Hilchenbach, M., Kleine, T., and Grundmann, J. T. and the APOSSUM TEAM: Snatching a sample of a genuine Near-Earth Asteroid: A very swift sample return opportunity, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-98, https://doi.org/10.5194/epsc2024-98, 2024.