OSIRIS-REx is a sample return mission to near-Earth Asteroid (101955) Bennu (Lauretta et al. 2017). The asteroid is spectrally classified as a B-type (Clark et al. 2011), and phyllosilicates similar to those found in carbonaceous chondrites have been detected on its surface (Hamilton et al. 2019). Bennu has a relatively flat (and blue) reflectance spectrum in the 0.4 to 3.7 micron spectral range and has a low albedo of ~4.5% (Golish et al. 2020).Bennu has a rough and rocky surface. Imaging data from the OSIRIS-REx Camera Suite (OCAMS; Rizk et al. 2018) reveals that boulders in the size range from 1 to 10 meters dominate the surface (Lauretta et al. 2019; DellaGiustina and Emery et al. 2019). Observed boulder textures range from smooth to hummocky and breccia-like (Walsh et al. 2019; DellaGiustina and Emery et al. 2019). The smoother rocks appear to be smaller, brighter, and more angular, while the rougher rocks appear to be larger, darker, and highly textured. Because spectral variations on Bennu are subtle and associated with albedo (Clark et al. 2019), the question arises: Could the observed color variations be due to texture variations alone, or are space-weathering variations required to explain the observations? To isolate the spectral effects of texture on the spectral properties of Bennu, we first simulate Bennu’s spectrum using a two-component mixture, then we check to see whether texture changes in this analog can account for the observed color and albedo trends. Simulated Bennu Spectral Analog: We synthesized physical mixtures of saponite (SAP105 with ~25 wt.% dolomite) with two forms of carbon:

1. Introduction Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) is a NASA New Frontiers mission to return a sample of near-Earth asteroid (101955) Bennu. The OSIRIS-REx spacecraft is equipped with a suite of scientific instruments [1], including the OSIRIS-REx Camera Suite (OCAMS) and the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS), among others. OCAMS’s high-spatial-resolution images of Bennu’s surface facilitate the identification of regions of interest, characterization of surface morphology, and mapping of relative surface albedo [2]. OVIRS is a point spectrometer that measures surface composition [3]. The OVIRS footprint during the Reconnaissance phase of the mission [1] had an observational field of view with diameters between 5 to 9 m. We search for and distinguish organics and carbonates on the surface of Bennu by studying the shape of the 3.4-micron feature, as observed by the OVIRS spectrometer during reconnaissance of candidate sampling sites [4]. Aliphatic organics have vibrational stretching bands at 3.4 microns, and the CO32- anion in carbonate minerals has an overtone of a fundamental asymmetric vibrational stretch, also at 3.4 microns. Organics on asteroids are hypothesized to be related to the organic materials delivered to Earth during the early bombardment phase of Earth’s development [5]. Carbonates record evidence of aqueous processes on Bennu [6], and together the organics and carbonates provide evidence for Bennu’s alteration history. We present the results of a search for Bennu spectral matches to specific laboratory carbonate spectra and meteoritic aliphatic organic spectra, in the wavelength range from 3.2 to 3.6 microns. The carbonate spectra were obtained from the RELAB facility at Brown University [7], and the insoluble organic material (IOM) spectra were obtained from [8]. For the carbonates, we test ~10 representative spectra each of calcite, dolomite, and magnesite. For the organic IOM, we test spectra such as Tagish Lake, Cold Bokkeveld, Mighei, Murchison, and Orgueil. 2 Data collection and preparation 2.1 Spectrum preparation To prepare laboratory and OVIRS spectra for band-match testing, we first divide every spectrum by a continuum, defined as a second order polynomial. The parabola is constrained using reflectance values at the wavelengths 2.95, 3.24, 3.6 microns. We then “stretch” the band by normalizing each spectrum such that the band minimum occurs at 0.0 and the maximum occurs at 1.0. Thus, we are only comparing the band shapes, as all other quantitative information has been removed by the continuum normalization and the band stretching. 2.2 K-S parameter test We apply a Kolmogorov-Smirnov (K-S) parameter test to find which laboratory spectra best fit the OVIRS spectra. We compare each laboratory spectrum to the entire OVIRS data set. The K-S parameter is an evaluation of the maximum discrepancy between two cumulative distribution functions (Figure 1). That is, we calculate the cumulative sum of the laboratory and OVIRS spectra and find the points of maximum discrepancy. The smaller the discrepancy, the better the fit. 3 Results Figure 1 shows an example match between an OVIRS spectrum from Bennu and a laboratory spectrum of calcite. Because the K-S parameter has a very low value (<0.013), we consider this a strong calcite detection. We perform the same test for the different types of carbonates and detect calcite more frequently than dolomite or magnesite. We perform the K-S test for all different types of IOM in our spectral library, and we find good matches on Bennu for the IOM in the Tagish Lake, Cold Bokkeveld, Mighei, Murchison, and Orgueil meteorites. We will present maps of where carbonate and organic material is detected on Bennu and discuss our search for associations or correlations with boulders or other surface properties. Acknowledgements This material is based upon work supported by NASA under Contract NNM10AA11C issued through the New Frontiers Program. INAF participation was supported by Italian Space Agency grant agreement n. 2017-37-H.0. We are grateful to the entire OSIRIS-REx Team for making the encounter with Bennu possible. References [1] Lauretta, D.S. et al. (2017). OSIRIS-REx: Sample Return from Asteroid (101955) Bennu. Space Sci. Rev. 212, 925–984. [2] Rizk, B. et al. OCAMS: the OSIRIS-REx camera suite. Space Sci Rev (2018) 214:26 https://doi.org/10.1007/s11214-017-0460-7 [3] Reuter, D.C. et al. (2018). The OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS): Spectral Maps of the Asteroid Bennu. Space Sci. Rev. 214, 54. [4] V. E. Hamilton. VNIR-TIR spectroscopy of (101955) Bennu. This conference. [5] Anders, Edward. Pre-biotic organic matter from comets and asteroids. Nature 342.6247 (1989): 255-257. [6] Kaplan, H. H., et al. Evidence of Organics and Carbonates on (101955) Bennu. LPI 2326 (2020): 1050. [7] Pieters, C.M., et al. Reflectance Experiment Laboratory (RELAB) Description and User's Manual. NASA Technical Reports Server. (2004). Document ID, 20040129713 [8] Kaplan, H.H., et al. Reflectance spectroscopy of insoluble organic matter (IOM) and carbonaceous meteorites. Meteorit Planet Sci, 54 (2019): 1051-1068. doi:10.1111/maps.13264

.IntroductionNASA’s OSIRIS-REx (Origins, Spectral Interpretations, Resource Identification, and Security–Regolith Explorer) asteroid sample return mission (Lauretta et al., 2017) began operating in proximity to near-Earth asteroid (101955) Bennu in December 2018. Here we present an analysis of the global photometry of Bennu from measurements by the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS; Reuter et al., 2018). This instrument is a point spectrometer with a wedged filter design. OVIRS is used for the spectral characterization of the surface of Bennu, with a field of view of 4 mrad and an effective spectral range from 0.4 to 4.3 μm. Our work focuses on OVIRS data acquired from December 9, 2018, to September 26, 2019.2.DatasetThis study comprises the global observation data from Preliminary Survey and the two sub-phases of Detailed Survey, Baseball Diamond (BBD) and Equatorial Stations (EQ) (campaigns described in Lauretta et al., 2017). We use a total of 299,702 calibrated spots. More details about the data selection and calibration are introduced by Zou et al. (submitted).3.Photometric analysesWe model the scattering properties of the surface of Bennu using the Lommel-Seeliger, Minnaert, McEwen, and Akimov photometric models. The best-fit model is a McEwen model with an exponential phase function and an exponential polynomial partition function. We use this model to correct the OVIRS spectra of Bennu to a standard reference viewing and illumination geometry at visible to infrared wavelengths for the purposes of global spectral mapping (Figure 1). We derive a bolometric Bond albedo map in which Bennu’s surface values range from 0.021 to 0.027. We find a phase reddening effect of 1.4±0.3 × 10−4 μm−1deg−1 across the wavelength range 0.48 to 2.5 μm, and our model is effective at removing this phase reddening.We compare our OVIRS results to Golish et al. (2020)’s report on the global photometry of Bennu, based on imaging data from the OSIRIS-REx Camera Suite (OCAMS; Rizk et al., 2018). We also compare the results to ground observation and other minor planets including Ryugu.Acknowledgements: This material is based upon work supported by NASA under Contract NNM10AA11C issued through the New Frontiers Program. We are grateful to the entire OSIRIS-REx Team for making the encounter with Bennu possible and the exploration highly successful. X.-D. Zou and J.-Y. Li also acknowledge partial support from the Solar System Exploration Research Virtual Institute 2016 (SSERVI16) Cooperative Agreement (Grant NNH16ZDA001N), SSERVI-TREX to the Planetary Science Institute. M. A. Barucci acknowledges funding support from CNES. ReferencesBennett, C.A., et al. 2020. A high-resolution global basemap of (101955) Bennu. Icarus. doi: 10.1016/j.icarus.2020.113690.Ernst et al., 2018, The Small Body Mapping Tool (SBMT) for Accessing, Visualizing, and Analyzing Spacecraft Data in Three Dimensions, LPSC 49, abstract no. 1043.Golish, D.R., et al. 2020. Disk-resolved photometric modeling and properties of asteroid (101955) Bennu. Icarus, doi:10.1016/j.icarus.2020.113724.Lauretta, D.S., et al. 2017. OSIRIS-REx: sample return from asteroid (101955) Bennu. Space Science Reviews 212(1-2):925-984.Reuter, D.C., et al. 2018. The OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS): spectral maps of the asteroid Bennu. Space Science Reviews 214(2):54.Rizk, B., et al. 2018. OCAMS: the OSIRIS-REx Camera Suite. Space Science Reviews 214(1):26.Zou et al. (submitted). Photometry of asteroid (101955) Bennu with OVIRS on OSIRIS-REx. Icarus.Figure 1. A global 3D facet-based map of the photometrically corrected (to 30°, 0°, 30°) OVIRS spots at a wavelength of 0.55 μm. The data are overlain on the OCAMS imaging basemap (Bennett et al., 2020), as viewed in the Small Body Mapping Tool (Ernst et al. 2018). Input spectra were obtained during Detailed Survey EQ3.

Manganese has been observed on Mars by the NASA Curiosity rover in a variety of contexts and is an important indicator of redox processes in hydrologic systems on Earth. Within the Murray formation, an ancient primarily fine-grained lacustrine sedimentary deposit in Gale crater, Mars, have observed up to 45x enrichment in manganese and up to 1.5x enrichment in iron within coarser grained bedrock targets compared to the mean Murray sediment composition. This enrichment in manganese coincides with the transition between two stratigraphic units within the Murray: Sutton Island, interpreted as a lake margin environment, and Blunts Point, interpreted as a lake environment. On Earth, lacustrine environments are common locations of manganese precipitation due to highly oxidizing conditions in the lakes. Here, we explore three mechanisms for ferromanganese oxide precipitation at this location: authigenic precipitation from lake water along a lake shore, authigenic precipitation from reduced groundwater discharging through porous sands along a lake shore, and early diagenetic precipitation from groundwater through porous sands. All three scenarios require highly oxidizing conditions and we discuss oxidants that may be responsible for the oxidation and precipitation of manganese oxides. This work has important implications for the habitability of Mars to microbes that could have used Mn redox reactions, owing to its multiple redox states, as an energy source for metabolism. In May 2017, the NASA Curiosity rover observed higher than usual amounts of manganese in the lakebed rocks within Gale crater, Mars. These sedimentary rocks have larger grain sizes than what is typical for the lakebed rocks in Gale crater. This may indicate that the original sediments were formed in a river, delta, or near the shoreline in the ancient lake. In this paper, we discuss how manganese could have been enriched in these rocks-for example, by percolation of groundwater through the original sediments or through the rock afterward-and what oxidant could be responsible for the precipitation of manganese in the rocks. On Earth, manganese becomes enriched because of oxygen in the atmosphere and this process is often sped up by the presence of microbes. Microbes on Earth can use the many oxidation states of manganese as energy for metabolism; if life was present on ancient Mars, the increased amounts of manganese in these rocks along the lake shore would be a helpful energy source for life. Enrichments of MnO are observed in bedrock and diagenetic features near a stratigraphic boundary between possible lake margin and lake sediments Manganese precipitation may have occurred along a lake shoreline via authigenic or early diagenetic scenarios All alteration scenarios require persistent water and highly oxidizing conditions in what would have been a habitable environment

NASA’s OSIRIS-REx mission set out in September of 2016 to survey and sample the near-Earth asteroid (101955) Bennu. During observations of Bennu, mission scientists observed centimeter-scale pebbles ejecting off the surface of the asteroid [1]. Many of these particles have been observed to follow hyperbolic trajectories, and the intersection of the orbits of Bennu and Earth suggests the possibility of particle flux at Earth [2]. We simulate the evolution of the motion of particles ejected from Bennu with a focus on potential meteor activity at Earth. We developed a complex simulated environment that accounts for the most potent perturbing gravitational bodies and solar radiation forces that are applicable to our centimeter-scale size range [3]. We use REBOUND, an orbital integration API developed by Hanno, Rien and Tamayo [4], augmented with REBOUNDx, developed by Tamayo et al. [5], to include solar radiation pressure and Poynting-Robertson (PR) drag. Bennu is modeled as a massless object, though great care is spent ensuring Bennu’s orbital accuracy as the particles are integrated towards well-defined close approaches in the near future [6]. Contrary to most meteoroid stream evolution studies, our simulations release particles from Bennu at a regular cadence (600 grams per week) throughout its orbit to resemble mission observations. To test the accuracy of the model and integrator, we prepared test cases for expected behavior. Recreating examples of particle resonance traps due to PR drag confirmed the implementation of the non-gravitational forces. Observations of the particle stream circularization (Fig. 1) and associability over time were also indicative of expected behavior. Additionally, planetary bodies were initialized from a JPL ephemeris (DE 431) and continuously compared to these values as a reference. The modeled solar system maintained an accuracy of 10-1 to 101 arcseconds of mean anomaly for their expected positions, giving us confidence in our methods. Towards the main objective of observing Earth-particle interactions, limitations in processing power and time encourage us to run simulations at particle production rates lower than the mass loss observed at Bennu by a factor of 100. Earth-particle close approaches are recorded annually during simulations. These data are later converted into stream density estimates and Earth impact probabilities through analysis on the B-plane [7]. This formalism enables the calculation of the statistical likelihood of impact with Earth for all of the particles produced in the simulation over the 348 years of interest (1788–2135); the years over which Bennu’s position is best constrained [6]. Such results now inform our conclusions on zenith hourly rate flux measurements at Earth. This work will be of practical importance for professional and amateur astronomers searching for Bennuid meteors. While the exact particle production mechanisms are still open to debate, we are hopeful that this initial work can be generalized to encompass the entire near-Earth asteroid population. This work, together with additional particle ejection observations and analyses from the OSIRIS-REx mission, will pave the way to a full understanding of this astronomical phenomenon.References:[1] D.S. Lauretta and C.W. Hergenrother et al. (2019). Science 366, 1217-1227.[2] Q. Ye (2019) Notes of the AAS 3, 56.[3] P. Jenniskens et al. (2011) Icarus 216, 40-61, & cams.seti.org[4] H. Rien and S.F. Liu (2012) Astronomy & Astrophysics 537, A128.[5] Tamayo, Daniel, et al. (2020) Monthly Notices of the Royal Astronomical Society 491.2[6] S.R. Chesley et al. (2014) Icarus 235, 5-22[7] D. Farnocchia et al. (2019) Springer, Celestial Mechanics and Dynamical Astronomy.

Two asteroid sample return missions studied, in-situ, two primitive asteroid targets to unravel their physical and chemical properties as well as obtain regolith samples for return to Earth. We describe remote observations from OSIRIS-REx and Hayabusa2 to determine the hydration content of these primitive asteroid surfaces and implications for their aqueous alteration histories. The NASA mission—Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer—OSIRIS-REx [1] studied the asteroid (101955) Bennu for two and a half years starting on its arrival at the asteroid on December 2018. The sample collection of surface regolith occurred on October 20th 2020 followed by the spacecraft departure from the asteroid on May 10th 2021 to begin its return cruise to deliver the sample to Earth in September 2023. The JAXA mission Hayabusa2 [2] studied the asteroid (162173) Ryugu for a year and a half (June 2018 to November 2019), and the twice-collected regolith samples with the re-entry capsule landed on Earth on December 5th 2020. These samples are currently being analyzed in Earth laboratories. Both missions had a near-infrared spectrometer onboard, amongst other instruments, which are the OVIRS spectrometer (OSIRIS-REx Visible and InfraRed Spectrometer) [3] and the NIRS3 spectrometer (Near-Infrared Spectrometer) [4]. The analysis of the asteroid surface reflectance spectra revealed the presence of an absorption band associated with OH/H2O centered near 2.74 microns [5] for asteroid Bennu and 2.72 microns for asteroid Ryugu [6]. This absorption band is caused by hydrated phyllosilicates across both asteroid surfaces. The absorption band, however, differs in center, shape and strength between the two asteroids with a weak and narrow band in the case of Ryugu and a wide asymmetric band for Bennu. This leads to the diagnoses of OH-bearing phyllosilicates on Ryugu [6] while H2O- and OH-bearing phyllosilicates on Bennu [5]. A similar absorption band has been observed in laboratory spectra of carbonaceous chondrite meteorites [7, 8]. Separately, the meteorite H content for many of these meteorites was measured by Alexander et al. [9, 10]. Correlations between spectral parameters computed on the hydrated phyllosilicate absorption band of clay minerals and their laboratory-measured water content was found by Milliken et al. [11, 12, 13] and absolute water estimation of Mars regolith was performed by [14]. As described in Praet et al. [15, 16], the normalized optical path length (NOPL) and effective single-scattering albedo (ESPAT) spectral parameters have been applied to estimate the hydrated phyllosilicates water and hydroxyl group hydrogen content (hereafter H content) of each asteroid global average surface. The estimation of the global mean H content of Bennu is 0.71 ± 0.28 wt.% and 0.52 −0.21+0.16 wt.% for Ryugu. In the case of Bennu, the H content surface distribution shows a correlation with the geomorphology with higher values in the high latitudes and lower values in the equatorial band (between –20° and 20° latitudes). Whereas no such correlation is evident in the case of Ryugu as the NOPL and ESPAT parameter computed across its surface do not display any correlation with its surface geomorphological structures. These estimates and spatial trends will be updated as new information is derived from the returned samples (e.g., with enhanced thermal tail removal). The estimated global H content value for Bennu is consistent with the H content range of aqueously altered meteorites such as heated CMs and C2 Tagish Lake, which is in agreement with [5, 16, 18]. As for Ryugu, its global H content is most similar to more strongly heated CMs, which is coherent with the best meteorite analogs for Ryugu near-infrared spectra (thermally metamorphosed CIs and shocked CMs) [6]. Our estimates of phyllosilicate water and hydroxyl group hydrogen content on Bennu and Ryugu, if confirmed by laboratory analysis on both returned samples, will allow the application of the same method to other asteroids, observed from the ground, and from space-telescopes. For asteroids with spectra exhibiting hydrated phyllosilicate absorption bands, such as the ones collected by the AKARI spectral survey [19] for example, estimation of their global mean H content will be possible. The study of water and hydroxyl abundance on primitive asteroids is important for understanding the origin of terrestrial water and to constrain dynamical models and evolutionary processes to better understand the origin and evolution of our Solar System. Acknowledgments We are grateful to the entire OSIRIS-REx Team for making the encounter with Bennu possible. This material is based upon work supported by NASA under Contract NNM10AA11C issued through the New Frontiers Program. We also thank the Hayabusa2 JAXA teams for their efforts in making the mission successful. AP and MAB acknowledge funding support from CNES. References [1] Lauretta D. S. et al. (2017) Space Sci. Rev., 212, 925-984. [2] Tsuda ,Y., Yoshikawa, M., Abe, M., Minamino, H., Nakazawa, S. (2013) Acta Astronaut., 91, 356–362. [3] Reuter, D.C. et al. (2018) Space Sci. Rev., 214, 54. [4] Iwata, T., Kitazato, K., Abe, M., et al. (2017), Space Science Reviews, 208, 317. [5] Hamilton, V.E. et al. (2019) Nature Astron., 3, 332. [6] Kitazato, K. et al. (2019) Science, DOI: 10.1126/science.aav7432. [7] Takir, D. et al. (2013) Meteorit. Planet. Sci., 48, 1618–1637. [8] Takir, D. et al. (2019) Icarus, 333, 243–251. [9] Alexander, C.M.O’D. et al. (2012) Science, 337, 721- 723. [10] Alexander, C.M.O’D. et al. (2013) Geochim. Cosmochim. Acta, 123, 244-260. [11] Milliken, R.E., Mustard J.F. (2005) JGR, 110, E12001. [12] Milliken, R.E., Mustard, J.F. (2007a) Icarus,189(2), 574-588. [13] Milliken, R.E., Mustard, J.F. (2007b) Icarus, 189, 550–573. [14] Milliken, R.E., et al. (2007). J. Geophys. Res. 112, E08S07, doi: 10.1029/2006JE002853. [15] Praet, A. et al. (2021a) Icarus, 363, 114427, doi: 10.1016/j.icarus.2021.114427. [16] Praet, A. et al. (2021b) Astron. Astrophys. doi: 10.1051/0004-6361/202140900. [17] Hamilton, V.E. et al., (2021) Astron. Astrophys. doi: 10.1051/0004-6361/202039728. [18] Hanna, R.D. et al. (2020) Icarus, 346, 113760. [19] Usui, F., Hasegawa, S., Ootsubo, T., Onaka, T. (2019). Publ. Astr. Soc. Japan 71.

OVIRS [1, 2] acquired visible to near-infrared spectra of asteroid Bennu’s surface showing an asymmetric absorption band centered at 2.74 ± 0.01 μm [3], attributed to the presence of hydrated phyllosilicates. This feature is widespread across Bennu’s surface. Such an absorption band has been detected in some carbonaceous chondrite meteorites [4, 5].In this study, we report the results from two distinct methods to estimate the hydration of Bennu’s surface. We calculated the normalized optical path length (NOPL) as well as the effective single particle absorption thickness (ESPAT) [6, 7, 8] on Bennu’s hydration band and on the selected meteorite spectra. For both methods, we compare meteorite results with their H2O/OH– H content, to estimate a H2O/OH– H content of Bennu’s average surface. Carbonaceous chondrite meteorite H2O/OH– H contents are derived from laboratory studies [9, 10]. Bennu spectra. Analysed spectra were acquired by OVIRS during Equatorial Station 3 (EQ3) of the Detailed Survey mission phase, on May 9, 2019, at 12:30 pm local solar time [11]. The reflectance spectra have been calibrated and photometrically corrected to an incidence angle of 0°, emission angle of 30°, and phase angle of 30°, using a McEwen photometrical model [12].Meteorite spectra. We used three sets of meteorite absolute reflectance spectra, from [4,5], [8], and [13]. For each set, powdered meteorite sample spectra were measured under vacuum (asteroid-like conditions).We selected over 40 meteorites for which bulk H values have been independently measured [9, 10]. In the case of Orgueil, Bells, and Tagish Lake, several samples were analysed and several H contents were ultimately derived [9, 14], all of which were used. Normalized Optical Path Length (NOPL). The NOPL parameter was calculated as described in [6, 7, 8] on each meteorite spectrum, each individual Bennu reflectance spectrum, and the global average spectrum of Bennu. A linear continuum was fitted from 2.67 to 3.3 μm. The wavelength, at which the NOPL parameter is calculated, is the mean band minimum position for the EQ3 data set at 2.73 μm. Methods used to locate the band minimum are described in [3].Effective Single Particle Absorption Thickness (ESPAT). The ESPAT parameter was calculated following the method of [6, 7, 8]. Absolute reflectance spectra of meteorites and Bennu’s surface were first converted into single-scattering albedo spectra [6, 7, 8]. A linear continuum was then fitted from 2.67 to 3.3 μm and the ESPAT parameter is calculated at 2.73 μm as well. Our analyses do not include the organic absorption bands, present longwards of ~3.3 μm [11, 15]. Thus, we compare NOPL and ESPAT results with the hydrogen content of H2O/OH– groups in hydrated phyllosilicates only, measured for the selected meteorites [9, 10]. Figure 1 shows the NOPL parameter variations across Bennu’s surface using EQ3 spectra.Figure 1: Map of NOPL values computed at 2.73 μm for each EQ3 spectrum of Bennu.We find a linear correlation (Figure 2) between the NOPL parameter calculated at 2.73 μm on meteorite spectra and the meteorite H2O/OH– H content.Using this linear correlation, for the NOPL calculated on Bennu’s EQ3 average spectrum, we estimate a H2O/OH– H content for Bennu’s average surface of 0.54 ± 0.11 wt.%. Figure 2: Linear correlation between NOPL calculated at 2.73 μm and H2O/OH– H content of the seven selected meteorites (in colored points), and for average Bennu (blue circle).As with the NOPL parameter, we also find a linear correlation between the ESPAT parameter calculated at 2.73 μm on meteorite spectra and the meteorite H2O/OH– H content. We therefore estimate a H2O/OH– H content for Bennu’s average surface of 0.49 ± 0.13 wt.%, using Bennu’s EQ3 mean ESPAT value and the latter correlation. Discussion and ConclusionThe H2O/OH– H content for Bennu’s average surface obtained using NOPL parameters is consistent with the range obtained with the ESPAT parameter. Both methods are based on estimating global H content (in H2O/OH– groups of hydrated phyllosilicates) by analogy with meteorite data. The values of H2O/OH– H content of Bennu’s average surface we obtained are 0.54 ± 0.11 and 0.49 ± 0.13 wt.% using the NOPL parameter and the ESPAT parameter, respectively. From our results (Figure 2), Bennu’s average surface is most similar to heated CMs and Tagish Lake. Both estimated H2O/OH– H content ranges of Bennu’s average surface are more consistent with those of CM meteorites (0.46–1.36 wt%), Tagish Lake (0.50–0.69 wt.%), CR meteorites (0.30–1.20 wt.%), and CO meteorites (0.49–0.52 wt.%) [3, 9]. The gaussian modeling of the hydration band will complete those results. AcknowledgementsThis material is based on work supported by NASA under Contract NNM10AA11C issued through the New Frontiers Program. AP, MAB, FM, SF, PH and JDPD acknowledge funding support by CNES. INAF participation was supported by Italian Space Agency grant agreement n. 2017-37-H.0. We are grateful to the entire OSIRIS-REx Team for making the encounter with Bennu possible. References[1] Lauretta D. S. et al. (2017) Space Sci. Rev. 212, 925-984. [2] Reuter D. C. et al. (2018) Space Sci. Rev. 214, 54. [3] Hamilton V. E. et al. (2019) Nat. Astron. 3, 332. [4] Takir D. et al. (2013) Meteorit. Planet. Sci. 48, 1618–1637. [5] Takir D. et al. (2019) Icarus 333, 243–251. [6] Milliken R. E. et Mustard J. F. (2005) JGR, 110, E12001. [7] Milliken R. E. et al. (2007) JGR, 112, E08S07. [8] Garenne A. et al. (2016) Icarus, 264, 172-183. [9] Alexander C.M.O’D. et al. (2012) Science, 337, 721-723. [10] Alexander C.M.O’D. et al. (2013) Geochim. Cosmochim. Acta, 123, 244-260. [11] Simon et al. (in revision) Science. [12] Zou X.-D. et al., this meeting. [13] Potin S. et al. (2020) Icarus, 348, 113826. [14] Gilmour C. M. et al. (2019) Meteorit. Planet. Sci. 54, 1951–1972. [15] Kaplan et al. (2020) LPSC LI, 1050.

Abstract Carbonaceous rubble pile asteroid 101955 Bennu was observed by the OSIRIS-REx Thermal Emission Spectrometer (OTES) at different times of the day with different surface temperatures. Prior results from OSIRIS-REx revealed that hydrated minerals are ubiquitous on Bennu, and OTES showed that Bennu’s surface is dominated by highly hydrated minerals, such those found in the bulk matrix of CI, CM and some CR carbonaceous chondrite meteorites. In this work, we analyzed the OTES spectroscopic behavior in response to the change in temperatures throughout the day, and we detected anomalous temperature-dependent variations of mid-infrared (5.71 to 100 µm) spectroscopic features. Correlating temperature-dependent variation of infrared features with mineralogical composition, we identified that 9% of Bennu surface is dominated by anhydrous minerals. This discovery further constraints Bennu's origin and evolutionary history. Bennu is made up of material reaccumulated after a catastrophic disruption of very different parent bodies. This identifies it as possible source of heterogeneous meteorite fall such as Kaidun and Almatha Sitta.

ABSTRACT The OSIRIS-REx spacecraft completed the first part of the primary objective by successfully sampling the surface of asteroid (101955) Bennu and storing the acquired sample in the re-entry capsule. The sampling ‘Touch-And-Go’ (TAG) maneuver was performed nominally at the primary sampling site, Nightingale, in Bennu’s Northern hemisphere. As a consequence of the TAG, material at the sampling site was mobilized and the morphology of the area was altered. This event offered a unique opportunity to investigate, in detail, the subsurface of asteroid Bennu giving access to fine grained and less altered material from Nightingale crater. We performed a detailed study on the infrared spectrum in the Nightingale region to search for modification resulting from the sampling event by analysing different features: slope, the H2O–OH− related absorption band in the $2.7\ \mu {\rm m}$ region, and other possible features. Our results show that, despite visible alteration of the TAG location detected by cameras, no strong variations are observed in the near-infrared bands and their quantitative evaluation is not possible beyond all the instrumental effects, although some changes may have occurred. We confirm that the infrared spectrum of the sampling site becomes redder with respect to the pre-TAG observations, conceivably due to fine material mobilization and exposure of less altered material, as confirmed by decreased spectral convexity. We identify possible modification of hydrated band at $2.7\ \mu {\rm m}$ but with some concerns due to data quality. However, our results place new constraints on the nature of Bennu’s subsurface material and the sample collected by OSIRIS-REx.

This paper summarizes the evidence for the optical effects of space weathering, as well as the properties of the surface that control optical changes, on asteroid (101955) Bennu. First, we set the stage by briefly reviewing what was known about space weathering of low-albedo materials from telescopic surveys, laboratory simulations, and sample return analysis. We then look at the evidence for the nature of space weathering on Bennu from recent spacecraft imaging and spectroscopy observations, including the visible to near-infrared and thermal infrared wavelengths, followed by other measurements such as normal albedo measurements from LIDAR scans. We synthesize these different lines of evidence in an effort to describe a general model of space weathering processes and resulting color effects on dark C-complex asteroids, with hypotheses that can be tested by analyzing samples returned by the mission.A working hypothesis that synthesizes findings thus far is that the optical effects of maturation in the space environment depend on the level of hydration of the silicate/phyllosilicate substrate. Subsequent variations in color depend on surface processes and exposure age. On strongly hydrated Bennu, in color imaging data, very young craters are darker and redder than their surroundings (more positive spectral slope in the wavelength range 0.4-0.7 mu m) as a result of their smaller particle sizes and/or fresh exposures of organics by impacts. Solar wind, dehydration, or migration of fines may cause intermediate-age surfaces to appear bluer than the very young craters. Exposed surfaces evolve toward Bennu's moderately blue global average spectral slope. However, in spectroscopic and LIDAR data, the equator, the oldest surface on Bennu, is darker and redder (wavelength range 0.55-2.0 mu m) than average and has shallower absorption bands, possibly due to dehydration and/or nanophase and/or microphase opaque production.Bennu is a rubble pile with an active surface, making age relationships, which are critical for determining space weathering signals, difficult to locate and quantify. Hence, the full story ultimately awaits analyses of the Bennu samples that will soon be delivered to Earth.

The first samples collected by the Mars 2020 mission represent units exposed on the Jezero Crater floor, from the potentially oldest Séítah formation outcrops to the potentially youngest rocks of the heavily cratered Máaz formation. Surface investigations reveal landscape‐to‐microscopic textural, mineralogical, and geochemical evidence for igneous lithologies, some possibly emplaced as lava flows. The samples contain major rock‐forming minerals such as pyroxene, olivine, and feldspar, accessory minerals including oxides and phosphates, and evidence for various degrees of aqueous activity in the form of water‐soluble salt, carbonate, sulfate, iron oxide, and iron silicate minerals. Following sample return, the compositions and ages of these variably altered igneous rocks are expected to reveal the geophysical and geochemical nature of the planet's interior at the time of emplacement, characterize martian magmatism, and place timing constraints on geologic processes, both in Jezero Crater and more widely on Mars. Petrographic observations and geochemical analyses, coupled with geochronology of secondary minerals, can also reveal the timing of aqueous activity as well as constrain the chemical and physical conditions of the environments in which these minerals precipitated, and the nature and composition of organic compounds preserved in association with these phases. Returned samples from these units will help constrain the crater chronology of Mars and the global evolution of the planet's interior, for understanding the processes that formed Jezero Crater floor units, and for constraining the style and duration of aqueous activity in Jezero Crater, past habitability, and cycling of organic elements in Jezero Crater.

Two of the instruments onboard the OSIRIS-REx spacecraft, the MapCam color imager and the OVIRS visible and infrared spectrometer, observed the surface of asteroid (101955) Bennu in partially overlapping wavelengths. Significant scientific advances have been enabled by using data from these two instruments in tandem, but a robust statistical understanding of their relationship is needed for future analyses to cross-compare their data as accurately and sensitively as possible. Here we present a cross-instrument comparison of data acquired by MapCam and OVIRS, including methods and results for all global and site-specific observation campaigns in which both instruments were active. In our analysis, we consider both the absolute radiometric offset and the relative (normalized) variation between the two instruments; we find that both depend strongly on the photometric and instrumental conditions during the observation. The two instruments have a large absolute offset (>15%) due to their independent radiometric calibrations. However, they are very consistent (relative offset as low as 1%) when each instrument's response is normalized at a single wavelength, particularly at low phase angles where shadows on Bennu's rough surface are minimized. We recommend using the global datasets acquired at 12:30 pm local solar time for cross-comparisons; data acquired at higher phase angles have larger uncertainties.

Samples returned from the carbonaceous (C-type) asteroid 162173 Ryugu by the Hayabusa2 mission were preliminarily analysed in a non-destructive manner. Their dark spectral features, small densities and absence of a high-temperature component imply that they are most similar to primitive CI group chondrites, but show some differences to known planetary materials.

NASA's first asteroid sample return mission, OSIRIS-REx, collected a sample from the surface of near-Earth asteroid Bennu in October 2020 and will deliver it to Earth in September 2023. Selecting a sample collection site on Bennu's surface was challenging due to the surprising lack of large ponded deposits of regolith particles exclusively fine enough ( ≤ 2 cm diameter) to be ingested by the spacecraft's Touch-and-Go Sample Acquisition Mechanism (TAGSAM). Here we describe the Sampleability Map of Bennu, which was constructed to aid in the selection of candidate sampling sites and to estimate the probability of collecting sufficient sample. "Sampleability" is a numeric score that expresses the compatibility of a given area's surface properties with the sampling mechanism. The algorithm that determines sampleability is a best fit functional form to an extensive suite of laboratory testing outcomes tracking the TAGSAM performance as a function of four observable properties of the target asteroid. The algorithm and testing were designed to measure and subsequently predict TAGSAM collection amounts as a function of the minimum particle size, maximum particle size, particle size frequency distribution, and the tilt of the TAGSAM head off the surface. The sampleability algorithm operated at two general scales, consistent with the resolution and coverage of data collected during the mission. The first scale was global and evaluated nearly the full surface. Due to Bennu's unexpected boulder coverage and lack of ponded regolith deposits, the global sampleability efforts relied heavily on additional strategies to find and characterize regions of interest based on quantifying and avoiding areas heavily covered by material too large to be collected. The second scale was site-specific and used higher-resolution data to predict collected mass at a given contact location. The rigorous sampleability assessments gave the mission confidence to select the best possible sample collection site and directly enabled successful collection of hundreds of grams of material.

Carbonaceous asteroids, such as (101955) Bennu, preserve material from the early Solar System, including volatile compounds and organic molecules. We report spacecraft imaging and spectral data collected during and after retrieval of a sample from Bennu’s surface. The sampling event mobilized rocks and dust into a debris plume, excavating a 9-meter-long elliptical crater. This exposed material is darker, spectrally redder, and more abundant in fine particulates than the original surface. The bulk density of the displaced subsurface material was 500 to 700 kilograms per cubic meter, which is about half that of the whole asteroid. Particulates that landed on instrument optics spectrally resemble aqueously altered carbonaceous meteorites. The spacecraft stored 250 ± 101 grams of material, which will be delivered to Earth in 2023.

The first robotically obtained samples of a carbonaceous asteroid have been safely returned to Earth. A non-destructive first-look analysis shows that asteroid Ryugu may be a CI chondrite with interesting variations.

SPECTRAL DATA. A. Praet, M. A. Barucci, P. H. Hasselmann, K. Kitazato, T. Iwata, M. Matsuoka, D. Domingue, and B. E. Clark. LESIA, Observatoire de Paris, PSL Research University, CNRS, Univ. de Paris, Sorbonne Université, 92195 Meudon, France (alice.praet@obspm.fr), The University of Aizu, Aizu-Wakamatsu 965-8580, Japan, ISAS, JAXA, Sagamihara 252-5210, Japan, Planetary Science Institute, Tucson, AZ 85710, USA, Department of Physics, Ithaca College, Ithaca, NY, USA.

The surfaces of airless bodies such as lunar and S-type asteroids typically become spectrally redder in visible to near-infrared reflectance with longer exposures to space weathering. However, some carbonaceous asteroids instead become spectrally bluer. Space weathering experiments on carbonaceous meteorites have provided some clues as to the space weathering products that could produce spectral bluing. We applied these experimental results to our Hapke radiative transfer model, with which we modeled spectral data from the OSIRIS-REx mission in order to determine whether these space weathering products-specifically, nanophase and microphase metallic iron, troilite, and magnetite-could explain the globally blue spectrum of the carbonaceous asteroid (101955) Bennu. The model suggests that the surface of Bennu has microphase iron, nanophase magnetite, and nanophase and microphase troilite. Considering previous space weathering experiments together with our spectral modeling of Bennu, we posit that the presence of nanophase magnetite is what causes a carbonaceous asteroid to become spectrally bluer with exposure time. Nanophase magnetite can form on asteroids that have Fe-bearing hydrated minerals (phyllosilicates). On anhydrous carbonaceous asteroids, nanophase iron forms instead of magnetite, leading to spectral reddening. We therefore predict that samples returned by the OSIRIS-REx mission from Bennu will have more nanophase magnetite than nanophase iron with nanophase and microphase sulfides, whereas samples returned by the Hayabusa2 mission from the carbonaceous asteroid (162173) Ryugu, which is spectrally red, will contain nanophase and microphase sulfides as well as more nanophase iron than nanophase magnetite.