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1. Comparison of optical spectra between asteroids Ryugu and Bennu: II. High-precision analysis for space weathering trends

Author

Yumoto, K., Tatsumi, E., Kouyama, T., Golish, D. R., Cho, Y., Morota, T., Kameda, S., Sato, H., Rizk, B., DellaGiustina, D. N., Yokota, Y., Suzuki, H., de León, J., Campins, H., Licandro, J., Popescu, M., Rizos, J. L., Honda, R., Yamada, M., Sakatani, N., Honda, C., Matsuoka, M., Hayakawa, M., Sawada, H., Ogawa, K., Yamamoto, Y., Lauretta, D. S., and Sugita, S.

Subjects
Astrophysics - Earth and Planetary Astrophysics, Physics - Space Physics
Abstract

The influence of space weathering on the observed spectra of C-complex asteroids remains uncertain. This has long hindered our understanding of their composition through telescope observations. Multi-band imaging of Ryugu by ONC-T on Hayabusa2 and that of Bennu by MapCam on OSIRIS-REx found opposite spectral trends of space weathering; Ryugu darkened/reddened while Bennu brightened/blued. How the spectra of Ryugu and Bennu evolved relative to each other would place a constraint for understanding their origins and evolutions. In this study, we compared the space weathering trends on Ryugu and Bennu by applying the results of cross calibration between ONC-T and MapCam. We show that the average Bennu surface is brighter by 18.0 $\pm$ 1.5% at 550 nm and bluer by 0.18 $\pm$ 0.03 $\mu$m$^{-1}$ (480-850 nm slope) than Ryugu. The spectral slopes of surface materials are more uniform on Bennu than on Ryugu at spatial scales $\gtrsim$1 m, but Bennu is more heterogeneous at $\lesssim$1 m. This suggests that lateral mixing due to resurfacing may have been more efficient on Bennu. The reflectance-spectral slope distributions of craters on Ryugu and Bennu appeared to follow two trend lines with an offset before cross calibration, but they converged to a single straight trend without a bend after cross calibration. We show that the spectra of the freshest craters on Ryugu and Bennu are indistinguishable within the uncertainty of cross calibration. These results suggest that Ryugu and Bennu initially had similar spectra before space weathering and that they evolved in completely opposite directions along the same trend line, subsequently evolving into asteroids with different disk-averaged spectra. These findings further suggest that space weathering likely expanded the spectral slope variation of C-complex asteroids, implying that they may have formed from materials with more uniform spectral slopes.

Published
2024
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2. Shaking and Tumbling: Short- and Long-Timescale Mechanisms for Resurfacing of Near-Earth Asteroid Surfaces from Planetary Tides and Predictions for the 2029 Earth Encounter by (99942) Apophis

Author

Ballouz, R. -L., Agrusa, H., Barnouin, O. S., Walsh, K. J., Zhang, Y., Binzel, R. P., Bray, V. J., DellaGiustina, D. N., Jawin, E. R., DeMartini, J. V., Marusiak, A., Michel, P., Murdoch, N., Richardson, D. C., Rivera-Valentín, E. G., Rivkin, A. S., and Tang, Y.

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

Spectral characterization of near-Earth asteroids (NEAs) has revealed a continuum of space-weathered states for the surfaces of S-complex NEAs, with Q-class NEAs, an S-complex subclass, most closely matching the un-weathered surfaces of ordinary chondrite meteorites. Dynamical calculations of the orbital evolution of S-complex NEAs revealed that Q-class NEAs tend to have close encounters with terrestrial planets, suggesting that planetary tides may play a role in refreshing NEA surfaces. However, the exact physical mechanism(s) that drive resurfacing through tidal encounters and the encounter distance at which these mechanisms are effective, has remained unclear. Through the lens of the upcoming (99942) Apophis encounter with Earth in 2029, we investigate the potential for surface mobilization through tidally-driven seismic shaking over short-timescales during encounter and subsequent surface slope evolution over longer-timescales driven by tumbling. We perform multi-scale numerical modeling and find that the 2029 encounter will induce short-term tidally-driven discrete seismic events that lead to high-frequency (>0.1 Hz) surface accelerations that reach magnitudes similar to Apophis' gravity, and that may be detectable by modern seismometers. It is still unclear if the shaking we model translates to widespread particle mobilization and/or lofting. We also find there will be a significant change in Apophis' tumbling spin state that could lead to longer-term surface refreshing in response to tumbling-induced surface slope changes. We propose that through these mechanisms, space-weathered S-class asteroid surfaces may become refreshed through the exposure of unweathered underlying material. These results will be tested by the future exploration of Apophis by NASA's OSIRIS-APEX., Comment: 39 pages, 11 figures, Accepted by The Planetary Science Journal

Published
2024

3. Comparison of optical spectra between asteroids Ryugu and Bennu:I. Cross calibration between Hayabusa2/ONC-T and OSIRIS-REx/MapCam

Author

Yumoto, K., Tatsumi, E., Kouyama, T., Golish, D. R., Cho, Y., Morota, T., Kameda, S., Sato, H., Rizk, B., DellaGiustina, D. N., Yokota, Y., Suzuki, H., de Leon, J., Campins, H., Licandro, J., Popescu, M., Rizos, J. L., Honda, R., Yamada, M., Sakatani, N., Honda, C., Matsuoka, M., Hayakawa, M., Sawada, H., Ogawa, K., Yamamoto, Y., Lauretta, D. S., and Sugita, S.

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

Asteroids (162173) Ryugu and (101955) Bennu observed by Hayabusa2 and OSIRIS-REx share many properties, but spectral observations by the telescopic Optical Navigation Camera (ONC-T) and MapCam detected subtle but significant differences, which may reflect differences in their origin and evolution. Comparing these differences on the same absolute scale is necessary for understanding their causes. However, ONC-T and MapCam have a large imager-to-imager systematic error of up to 15% caused by the difference in radiometric calibration targets. To resolve this problem, we cross calibrated albedo and color data between the two instruments using the Moon as the common calibration standard. The images of the Moon taken by ONC-T and MapCam were compared with those simulated using photometry models developed from lunar orbiter data. Our results show that the cross-calibrated reflectance of Ryugu and Bennu can be obtained by upscaling the pre-cross-calibrated reflectance of Bennu by 13.3 +/- 1.6% at b band, 13.2 +/- 1.5% at v band, 13.6 +/- 1.7% at w band, and 14.8 +/- 1.8% at x band, while those for Ryugu are kept the same. These factors compensate for the imager-to-imager bias caused by differences in targets used for radiometric calibration and solar irradiance models used for data reduction. Need for such large upscaling underscore the importance of using the cross-calibrated data for accurately comparing the Ryugu and Bennu data. The uncertainty in these factors show that the reflectance of Ryugu and Bennu can be compared with <2% accuracy after applying our results. By applying our cross calibration, the geometric albedo of Bennu became consistent with those observed by ground-based telescopes and OVIRS. Our result can be simply applied by multiplying a constant to the publicly available data and enables accurate comparison of the optical spectra of Ryugu and Bennu in future studies.

Published
2023
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5. Using artificial neural networks to improve photometric modeling in airless bodies

Author

Rizos, J. L., Asensio-Ramos, A., Golish, D. R., DellaGiustina, D. N., Licandro, J., de León, J., Campins, H., Tatsumi, E., and Popescu, M.

Subjects
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Earth and Planetary Astrophysics
Abstract

Relevant information about physical properties of the surface of airless bodies such as porosity, particle size, or roughness can be inferred knowing the dependence of the brightness with illumination and observing geometry. Additionally, this knowledge is necessary to standardize or photometrically correct data acquired under different illumination conditions. In this work we develop a robust, automatic, and efficient photometric modeling methodology which is tested and validated using Bennu images acquired by the camera MapCam from the OSIRIS-REx spacecraft. It consists of a supervised machine learning algorithm through an artificial neural network. Our system provides a more precise modeling for all color filters than the previous procedures which are already published, offering an improvement over this classic approach of up to 14.30%, as well as a considerable reduction in computing time.

Published
2021

6. Bennu's global surface and two candidate sample sites characterized by spectral clustering of OSIRIS-REx multispectral images

Author

Rizos, J. L., de Leon, J., Licandro, J., Golish, D. R., Campins, H., Tatsumi, E., Popescu, M., DellaGiustina, D. N., Pajola, M., Li, J. -Y., Becker, K. J., and Lauretta, D. S.

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

The OSIRIS-REx spacecraft encountered the asteroid (101955) Bennu on December 3, 2018, and has since acquired extensive data from the payload of scientific instruments on board. In 2019, the OSIRIS-REx team selected primary and backup sample collection sites, called Nightingale and Osprey, respectively. On October 20, 2020, OSIRIS-REx successfully collected material from Nightingale. In this work, we apply an unsupervised machine learning classification through the K-Means algorithm to spectrophotometrically characterize the surface of Bennu, and in particular Nightingale and Osprey. We first analyze a global mosaic of Bennu, from which we find four clusters scattered across the surface, reduced to three when we normalize the images at 550 nm. The three spectral clusters are associated with boulders and show significant differences in spectral slope and UV value. We do not see evidence of latitudinal non-uniformity, which suggests that Bennu's surface is well-mixed. In our higher-resolution analysis of the primary and backup sample sites, we find three representative normalized clusters, confirming an inverse correlation between reflectance and spectral slope (the darkest areas being the reddest ones) and between b' normalized reflectance and slope. Nightingale and Osprey are redder than the global surface of Bennu by more than $1\sigma$ from average, consistent with previous findings, with Nightingale being the reddest ($S' = (- 0.3 \pm 1.0) \times 10^{- 3}$ percent per thousand angstroms). We see hints of a weak absorption band at 550 nm at the candidate sample sites and globally, which lends support to the proposed presence of magnetite on Bennu.

Published
2021
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7. Overcoming the Challenges Associated with Image-based Mapping of Small Bodies in Preparation for the OSIRIS-REx Mission to (101955) Bennu

Author

DellaGiustina, D. N., Bennett, C. A., Becker, K., Golish, D. R, Corre, L. Le, Cook, D. A., Edmundson, K. L., Chojnacki, M., Sutton, S. S., Milazzo, M. P., Carcich, B., Nolan, M. C., Habib, N., Burke, K. N., Becker, T., Smith, P. H., Walsh, K. J., Getzandanner, K., Wibben, D. R., Leonard, J. M., Westermann, M. M., Polit, A. T., Kidd Jr., J. N., Hergenrother, C. W., Boynton, W. V., Backer, J., Sides, S., Mapel, J., Berry, K., Roper, H., d'Aubigny, C. Drouet, Rizk, B., Crombie, M. K., Kinney-Spano, E. K., de Leon, J., Rizos, J. L., Licandro, J., Campins, H. C., Clark, B. E., Enos, H. L., and Lauretta, D. S.

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

The OSIRIS-REx Asteroid Sample Return Mission is the third mission in NASA's New Frontiers Program and is the first U.S. mission to return samples from an asteroid to Earth. The most important decision ahead of the OSIRIS-REx team is the selection of a prime sample-site on the surface of asteroid (101955) Bennu. Mission success hinges on identifying a site that is safe and has regolith that can readily be ingested by the spacecraft's sampling mechanism. To inform this mission-critical decision, the surface of Bennu is mapped using the OSIRIS-REx Camera Suite and the images are used to develop several foundational data products. Acquiring the necessary inputs to these data products requires observational strategies that are defined specifically to overcome the challenges associated with mapping a small irregular body. We present these strategies in the context of assessing candidate sample-sites at Bennu according to a framework of decisions regarding the relative safety, sampleability, and scientific value across the asteroid's surface. To create data products that aid these assessments, we describe the best practices developed by the OSIRIS-REx team for image-based mapping of irregular small bodies. We emphasize the importance of using 3D shape models and the ability to work in body-fixed rectangular coordinates when dealing with planetary surfaces that cannot be uniquely addressed by body-fixed latitude and longitude., Comment: 31 pages, 10 figures, 2 tables

Published
2018

8. Expected spectral characteristics of (101955) Bennu and (162173) Ryugu, targets of the OSIRIS-REx and Hayabusa2 missions

Author

de León, J., Campins, H., Morate, D., De Prá, M., Alí-Lagoa, V., Licandro, J., Rizos, J. L., Pinilla-Alonso, N., DellaGiustina, D. N., Lauretta, D. S., Popescu, M., and Lorenzi, V.

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

NASA's OSIRIS-REx and JAXA's Hayabusa2 sample-return missions are currently on their way to encounter primitive near-Earth asteroids (101955) Bennu and (162173) Ryugu, respectively. Spectral and dynamical evidence indicates that these near-Earth asteroids originated in the inner part of the main belt. There are several primitive collisional families in this region, and both these asteroids are most likely to have originated in the Polana-Eulalia family complex. We present the expected spectral characteristics of both targets based on our studies of our primitive collisional families in the inner belt: Polana-Eulalia, Erigone, Sulamitis, and Clarissa. Observations were obtained in the framework of our PRIMitive Asteroids Spectroscopic Survey (PRIMASS). Our results are especially relevant to the planning and interpretation of in-situ images and spectra to be obtained by the two spacecraft during the encounters with their targets., Comment: 22 pages, 11 figures. Accepted for publication in Icarus on May 11, 2018

Published
2018
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9. OSIRIS-REx: Sample Return from Asteroid (101955) Bennu

Author

Lauretta, D. S., Balram-Knutson, S. S., Beshore, E., Boynton, W. V., dAubigny, C. Drouet, DellaGiustina, D. N., Enos, H. L., Gholish, D. R., Hergenrother, C. W., Howell, E. S., Johnson, C. A., Morton, E. T., Nolan, M. C., Rizk, B., Roper, H. L., Bartels, A. E., Bos, B. J., Dworkin, J. P., Highsmith, D. E., Lorenz, D. A., Lim, L. F., Mink, R., Moreau, M. C., Nuth, J. A., Reuter, D. C., Simon, A. A., Bierhaus, E. B., Bryan, B. H., Ballouz, R., Barnouin, O. S., Binzel, R. P., Bottke, W. F., Hamilton, V. E., Walsh, K. J., Chesley, S. R., Christensen, P. R., Clark, B. E., Connolly, H. C., Crombie, M. K., Daly, M. G., Emery, J. P., McCoy, T. J., McMahon, J. W., Scheeres, D. J., Messenger, S., Nakamura-Messenger, K., Righter, K., and Sandford, S. A.

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

In May of 2011, NASA selected the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) asteroid sample return mission as the third mission in the New Frontiers program. The other two New Frontiers missions are New Horizons, which explored Pluto during a flyby in July 2015 and is on its way for a flyby of Kuiper Belt object 2014 MU69 on Jan. 1, 2019, and Juno, an orbiting mission that is studying the origin, evolution, and internal structure of Jupiter. The spacecraft departed for near-Earth asteroid (101955) Bennu aboard an United Launch Alliance Atlas V 411 evolved expendable launch vehicle at 7:05 p.m. EDT on September 8, 2016, on a seven-year journey to return samples from Bennu. The spacecraft is on an outbound-cruise trajectory that will result in a rendezvous with Bennu in August 2018. The science instruments on the spacecraft will survey Bennu to measure its physical, geological, and chemical properties, and the team will use these data to select a site on the surface to collect at least 60 g of asteroid regolith. The team will also analyze the remote-sensing data to perform a detailed study of the sample site for context, assess Bennus resource potential, refine estimates of its impact probability with Earth, and provide ground-truth data for the extensive astronomical data set collected on this asteroid. The spacecraft will leave Bennu in 2021 and return the sample to the Utah Test and Training Range (UTTR) on September 24, 2023., Comment: 89 pages, 39 figures, submitted to Space Science Reviews - OSIRIS-REx special issue

Published
2017
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10. Fine-regolith production on asteroids controlled by rock porosity

Author

Cambioni, S., Delbo, M., Poggiali, G., Avdellidou, C., Ryan, A. J., Deshapriya, J. D. P., Asphaug, E., Ballouz, R.-L., Barucci, M. A., Bennett, C. A., Bottke, W. F., Brucato, J. R., Burke, K. N., Cloutis, E., DellaGiustina, D. N., Emery, J. P., Rozitis, B., Walsh, K. J., and Lauretta, D. S.

Published
2021
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12. Bennu's near-Earth lifetime of 1.75 million years inferred from craters on its boulders

Author

Ballouz, R.-L., Walsh, K. J., Barnouin, O. S., DellaGiustina, D. N., Asad, M. Al, Jawin, E. R., and Daly, M. G.

Subjects
Asteroids -- Natural history -- Observations, Craters -- Analysis, Chronology -- Analysis, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

An asteroid's history is determined in large part by its strength against collisions with other objects.sup.1,2 (impact strength). Laboratory experiments on centimetre-scale meteorites.sup.3 have been extrapolated and buttressed with numerical simulations to derive the impact strength at the asteroid scale.sup.4,5. In situ evidence of impacts on boulders on airless planetary bodies has come from Apollo lunar samples.sup.6 and images of the asteroid (25143) Itokawa.sup.7. It has not yet been possible, however, to assess directly the impact strength, and thus the absolute surface age, of the boulders that constitute the building blocks of a rubble-pile asteroid. Here we report an analysis of the size and depth of craters observed on boulders on the asteroid (101955) Bennu. We show that the impact strength of metre-sized boulders is 0.44 to 1.7 megapascals, which is low compared to that of solid terrestrial materials. We infer that Bennu's metre-sized boulders record its history of impact by millimetre- to centimetre-scale objects in near-Earth space. We conclude that this population of near-Earth impactors has a size frequency distribution similar to that of metre-scale bolides and originates from the asteroidal population. Our results indicate that Bennu has been dynamically decoupled from the main asteroid belt for 1.75 [plus or minus] 0.75 million years. Analysis of the size and depth of craters on boulders on the asteroid (101955) Bennu indicates that Bennu has been in near-Earth space for 1.75 [plus or minus] 0.75 million years., Author(s): R.-L. Ballouz [sup.1] , K. J. Walsh [sup.2] , O. S. Barnouin [sup.3] , D. N. DellaGiustina [sup.1] , M. Al Asad [sup.4] , E. R. Jawin [sup.5] , [...]

Published
2020
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13. The unexpected surface of asteroid (101955) Bennu

Author

Lauretta, D. S., DellaGiustina, D. N., Bennett, C. A., Golish, D. R., Becker, K. J., Balram-Knutson, S. S., Barnouin, O. S., Becker, T. L., Bottke, W. F., Boynton, W. V., Campins, H., Clark, B. E., Connolly, Jr, H. C., Drouet d’Aubigny, C. Y., Dworkin, J. P., Emery, J. P., Enos, H. L., Hamilton, V. E., Hergenrother, C. W., Howell, E. S., Izawa, M. R. M., Kaplan, H. H., Nolan, M. C., Rizk, B., Roper, H. L., Scheeres, D. J., Smith, P. H., Walsh, K. J., Wolner, C. W. V., and The OSIRIS-REx Team

Published
2019
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15. Cross calibration between Hayabusa2/ONC-T and OSIRIS-REx/MapCam for comparative analyses between asteroids Ryugu and Bennu

Author

Yumoto, K., Tatsumi, E., Kouyama, T., Golish, D. R., Kameda, S., Sato, H., Rizk, B., DellaGiustina, D. N., Yokota, Y., Suzuki, H., de León, J., Campins, H., Licandro, J., Popescu, M., Rizos, J. L., Honda, R., Yamada, M., Morota, T., Sakatani, N., Cho, Y., Honda, C., Matsuoka, M., Hayakawa, M., Sawada, H., Ogawa, K., Yamamoto, Y., Sugita, S., Lauretta, D. S., Yumoto, K., Tatsumi, E., Kouyama, T., Golish, D. R., Kameda, S., Sato, H., Rizk, B., DellaGiustina, D. N., Yokota, Y., Suzuki, H., de León, J., Campins, H., Licandro, J., Popescu, M., Rizos, J. L., Honda, R., Yamada, M., Morota, T., Sakatani, N., Cho, Y., Honda, C., Matsuoka, M., Hayakawa, M., Sawada, H., Ogawa, K., Yamamoto, Y., Sugita, S., and Lauretta, D. S.

Abstract

Proximity observations of (162173) Ryugu by the telescopic Optical Navigation Camera onboard Hayabusa2 and (101955) Bennu by MapCam onboard Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer found opposite spectral trends of space weathering on these carbonaceous asteroids. Whether the space weathering trends on these asteroids evolved from the same starting spectra would place an important constraint for understanding their relation. However, systematic error between data obtained by the two imagers needed to be reduced for accurate comparison. To resolve this problem, we cross calibrated albedo and color data using the Moon as the common standard. We show that the cross-calibrated reflectance can be obtained by upscaling the pre-cross-calibrated reflectance of Bennu by 12 +/- 2% at v-band, reducing the systematic errors down to 2%. The cross-calibrated data show that Bennu is brighter by 16 +/- 2% at v-band and bluer in spectral slope by 0.19 +/- 0.05 (/um) than Ryugu. The spectra of fresh craters on Ryugu and Bennu before cross calibration appeared to follow two parallel trend lines with offset, but they converged to a single trend after cross calibration. Such a post-cross-calibration perspective raise the possibility that Ryugu and Bennu evolved from materials with similar visible spectra but evolved in diverging directions by space weathering. The divergent evolution can be caused by the difference in space weathering dose/process and/or composition of the starting material. Thus, comparing the composition of samples returned from Ryugu and Bennu may change the way we interpret the spectral variation of C-complex asteroids.

Published
2023

16. The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations

Author

Hergenrother, C. W., Maleszewski, C. K., Nolan, M. C., Li, J.-Y., Drouet d’Aubigny, C. Y., Shelly, F. C., Howell, E. S., Kareta, T. R., Izawa, M. R. M., Barucci, M. A., Bierhaus, E. B., Campins, H., Chesley, S. R., Clark, B. E., Christensen, E. J., DellaGiustina, D. N., Fornasier, S., Golish, D. R., Hartzell, C. M., Rizk, B., Scheeres, D. J., Smith, P. H., Zou, X.-D., Lauretta, D. S., and The OSIRIS-REx Team

Published
2019
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17. OSIRIS‐REx Visible and Near‐Infrared Observations of the Moon

Author

Simon, A. A, Hanna, K. L. Donaldson, d'Aubigny, C. Y. Drouet, Poggiali, G, Emery, J. P, Brucato, J, Cosentino, R. G, Reuter, D. C, Golish, D. R, DellaGiustina, D. N, Lunsford, A, Gorius, N, Smith, P. H, and Lauretta, D. S

Subjects
Lunar And Planetary Science And Exploration
Abstract

The Origins, Spectral Interpretation, Resource Identification, and Security Regolith Explorer(OSIRISREx) mission observed the The Origins, Spectral Interpretation, Resource Identification, and Security‐Regolith Explorer (OSIRIS‐REx) mission observed the Moon during the spacecraft's Earth gravity assist in 2017. From the spacecraft view, the lunar phase was 42°, and the in‐view hemisphere was dominated by anorthositic highlands terrain. Lunar spectra obtained by the OSIRIS‐REx Visible and InfraRed Spectrometer show evidence of several candidate absorption features. We observe the 2.8‐μm hydration band, confirming the spectral results from other missions, but detected in full‐disk spectra. We also tentatively identify weak spectral features near 0.9 and 1.3 μm, consistent with lunar regolith containing a mixture of plagioclase and orthopyroxene minerals, as expected for highlands terrain.

Published
2019
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19. Regional Photometric Modeling of Asteroid (101955) Bennu

Author

Golish, D. R., primary, Li, J.-Y., additional, Clark, B. E., additional, DellaGiustina, D. N., additional, Zou, X.-D., additional, Rizos, J. L., additional, Hasselmann, P. H., additional, Bennett, C. A., additional, Fornasier, S., additional, Drouet d’Aubigny, C., additional, Rizk, B., additional, Daly, M. G., additional, Barnouin, O. S., additional, Seabrook, J. A., additional, Philpott, L., additional, Al Asad, M. M., additional, Johnson, C. L., additional, Rozitis, B., additional, Ryan, A. J., additional, Emery, J. P., additional, and Lauretta, D. S., additional

Published
2021
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20. Hemispherical differences in the shape and topography of asteroid (101955) Bennu

Author

Daly, M. G., primary, Barnouin, O. S., additional, Seabrook, J. A., additional, Roberts, J., additional, Dickinson, C., additional, Walsh, K. J., additional, Jawin, E. R., additional, Palmer, E. E., additional, Gaskell, R., additional, Weirich, J., additional, Haltigin, T., additional, Gaudreau, D., additional, Brunet, C., additional, Cunningham, G., additional, Michel, P., additional, Zhang, Y., additional, Ballouz, R.-L., additional, Neumann, G., additional, Perry, M. E., additional, Philpott, L., additional, Al Asad, M. M., additional, Johnson, C. L., additional, Adam, C. D., additional, Leonard, J. M., additional, Geeraert, J. L., additional, Getzandanner, K., additional, Nolan, M. C., additional, Daly, R. T., additional, Bierhaus, E. B., additional, Mazarico, E., additional, Rozitis, B., additional, Ryan, A. J., additional, DellaGiustina, D. N., additional, Rizk, B., additional, Susorney, H. C. M., additional, Enos, H. L., additional, and Lauretta, D. S., additional

Published
2020
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21. Asteroid (101955) Bennu’s weak boulders and thermally anomalous equator

Author

Rozitis, B., primary, Ryan, A. J., additional, Emery, J. P., additional, Christensen, P. R., additional, Hamilton, V. E., additional, Simon, A. A., additional, Reuter, D. C., additional, Al Asad, M., additional, Ballouz, R.-L., additional, Bandfield, J. L., additional, Barnouin, O. S., additional, Bennett, C. A., additional, Bernacki, M., additional, Burke, K. N., additional, Cambioni, S., additional, Clark, B. E., additional, Daly, M. G., additional, Delbo, M., additional, DellaGiustina, D. N., additional, Elder, C. M., additional, Hanna, R. D., additional, Haberle, C. W., additional, Howell, E. S., additional, Golish, D. R., additional, Jawin, E. R., additional, Kaplan, H. H., additional, Lim, L. F., additional, Molaro, J. L., additional, Munoz, D. Pino, additional, Nolan, M. C., additional, Rizk, B., additional, Siegler, M. A., additional, Susorney, H. C. M., additional, Walsh, K. J., additional, and Lauretta, D. S., additional

Published
2020
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22. OSIRIS-REx spectral analysis of (101955) Bennu by multivariate statistics

Author

Barucci, M. A., primary, Hasselmann, P. H., additional, Praet, A., additional, Fulchignoni, M., additional, Deshapriya, J. D. P., additional, Fornasier, S., additional, Merlin, F., additional, Clark, B. E., additional, Simon, A. A., additional, Hamilton, V. E., additional, Emery, J. P., additional, Howell, E. S., additional, Brucato, J. R., additional, Cloutis, E. A., additional, Zou, X. D., additional, Li, J.-Y., additional, Michel, P., additional, Ferrone, S., additional, Poggiali, G., additional, Reuter, D. C., additional, DellaGiustina, D. N., additional, and Lauretta, D. S., additional

Published
2020
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23. Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis

Author

DellaGiustina, D. N., Emery, J. P., Golish, D. R., Rozitis, B., Bennett, C. A., Burke, K. N., Ballouz, R.-L., Becker, K. J., Christensen, P. R., Drouet d’Aubigny, C. Y., Ireland, Trevor, DellaGiustina, D. N., Emery, J. P., Golish, D. R., Rozitis, B., Bennett, C. A., Burke, K. N., Ballouz, R.-L., Becker, K. J., Christensen, P. R., Drouet d’Aubigny, C. Y., and Ireland, Trevor

Abstract

Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennu’s surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennu’s moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennu’s surface particles span from the disruption of the asteroid’s parent body (boulders) to recent in situ production (micrometre-scale particles).

Published
2019

24. Overcoming the Challenges Associated with Image‐Based Mapping of Small Bodies in Preparation for the OSIRIS‐REx Mission to (101955) Bennu

Author

DellaGiustina, D. N., primary, Bennett, C. A., additional, Becker, K., additional, Golish, D. R., additional, Le Corre, L., additional, Cook, D. A., additional, Edmundson, K. L., additional, Chojnacki, M., additional, Sutton, S. S., additional, Milazzo, M. P., additional, Carcich, B., additional, Nolan, M. C., additional, Habib, N., additional, Burke, K. N., additional, Becker, T., additional, Smith, P. H., additional, Walsh, K. J., additional, Getzandanner, K., additional, Wibben, D. R., additional, Leonard, J. M., additional, Westermann, M. M., additional, Polit, A. T., additional, Kidd, J. N., additional, Hergenrother, C. W., additional, Boynton, W. V., additional, Backer, J., additional, Sides, S., additional, Mapel, J., additional, Berry, K., additional, Roper, H., additional, Drouet d'Aubigny, C., additional, Rizk, B., additional, Crombie, M. K., additional, Kinney‐Spano, E. K., additional, de León, J., additional, Rizos, J. L., additional, Licandro, J., additional, Campins, H. C., additional, Clark, B. E., additional, Enos, H. L., additional, and Lauretta, D. S., additional

Published
2018
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25. Episodes of particle ejection from the surface of the active asteroid (101955) Bennu.

Author

Lauretta, D. S., Hergenrother, C. W., Chesley, S. R., Leonard, J. M., Pelgrift, J. Y., Adam, C. D., Al Asad, M., Antreasian, P. G., Ballouz, R.-L., Becker, K. J., Bennett, C. A., Bos, B. J., Bottke, W. F., Brozović, M., Campins, H., Connolly Jr., H. C., Daly, M. G., Davis, A. B., de León, J., and DellaGiustina, D. N.

Subjects
ASTEROIDS, STRESS fractures (Orthopedics), THERMAL stresses, METEOROIDS
Abstract

Active asteroids are those that show evidence of ongoing mass loss. We report repeated instances of particle ejection from the surface of (101955) Bennu, demonstrating that it is an active asteroid. The ejection events were imaged by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) spacecraft. For the three largest observed events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. We also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the Bennu environment. We consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteoroid impacts, thermal stress fracturing, and secondary impacts. [ABSTRACT FROM AUTHOR]

Published
2021
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26. PHOTOGRAMMETRIC PROCESSING OF OSIRIS-REX IMAGES OF ASTEROID (101955) BENNU.

Author

Edmundson, K. L., Becker, K. J., Becker, T. L., Bennett, C. A., DellaGiustina, D. N., Golish, D. R., Porter, N. A., Rizk, B., Drouet d'Aubigny, C., Daly, M. G., Palmer, E., Weirich, J., Barnouin, O. S., Philpott, L., Al Asad, M. M., Seabrook, J. A., Johnson, C. L., and Lauretta, D. S.

Subjects
IMAGE processing, LASER altimeters, ASTEROIDS, IMAGE sensors, ELECTRONIC data processing
Abstract

The principal objective of the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission is to retrieve a sample of the asteroid (101955) Bennu and return it to Earth. OSIRIS-REx arrived at Bennu in December 2018. Images of the asteroid by the OSIRIS-REx Camera Suite (OCAMS) were photogrammetrically controlled to produce a global basemap and site-specific image mosaics essential to the selection of a primary and backup sample site, which were announced in December 2019. In the control process, OCAMS images were registered to shape models created from OSIRIS-REx Laser Altimeter (OLA) data and from the process of stereophotoclinometry. This paper summarizes the photogrammetric control to date of images collected at Bennu. We briefly review the mission and the OCAMS imaging sensors. We then describe the photogrammetric control process for the global mapping campaign and targeted reconnaissance surveys of candidate sample sites. Finally, we discuss ongoing and future work. [ABSTRACT FROM AUTHOR]

Published
2020
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27. QUANTITATIVE REFLECTANCE IMAGING OF SAMPLES RETURNED FROM ASTEROID BENNU.

Author

Fulford, R. E., Lauretta, D. S., Golish, D. R., and DellaGiustina, D. N.

Subjects
SPECTRAL reflectance, NEAR-earth asteroids, REFLECTANCE, COLD storage, IMAGING systems, SOLAR system, MULTISPECTRAL imaging, IMAGE analysis
Abstract

Instroduction: The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft arrived at its target, near-Earth asteroid (101955) Bennu, in December 2018. After one year of operating in proximity, the team selected a primary site for sample collection. In October 2020, the spacecraft descended to the surface of Bennu and collected a sample. The spacecraft departed Bennu in May 2021 and will return the sample to Earth in September 2023 [3]. The analysis of the returned sample will produce key data to determine this B-type asteroid's history and that of its components and precursor objects. Bennu's mineralogy, as inferred from spectral characterization [2], is dominated by (1) hydrated silicates, (2) carbonates, (3) magnetite, (4) organic components. Other phases, such as sulfides, that are not spectrally active may also be abundant in the returned sample. The presence of organics on its surface make it an object of astrobiological interest, as it may hold important information early solar system conditions, the origin of organics on Earth, and the delivery of water to Earth. Preliminary Examination: The Preliminary Examination phase of the mission will begin once the sample canister is opened at NASA's Johnson Space Center (JSC). One of the primary goals of Preliminary Examination is the selection of returned samples for the OSIRIS-REx Sample Analysis Team to address mission science goals (up to 25 wt. percent), and samples archived by NASA (75 wt. percent) to include samples for international agencies (CSA 4 wt. percent and JAXA 0.5 wt. percent), samples for remote storage at White Sands Complex (WSC), and samples for hermetically sealed or cold storage. Imaging Objectives: Quantitative reflectance imaging of the returned sample will occur soon after the Sample Return Capsule is opened at JSC. This characterization provides quantitative information on the reflectance of the sample for discrete wavelengths comparable to the filter set on MapCam [5] with additional wavelength bands added for more comprehensive broadband spectral characterization. The objective of this investigation is to rapidly assess the lithological diversity using normal reflectance and spectral band ratios, similar to the color imaging of Bennu [1]. After evaluating the number of distinct lithologies, we will organize our scientific investigations with reference to our coordinated analysis investigation plan to ensure characterization of all major lithologies and a subset of minor lithologies, depending the heterogeneity of the material. Science Operations Proficiency Integrated Exercise 1 (SOPIE-1): A prototype Quantitative Reflectance Imaging System (QRIS) was used at OSIRIS-REx's Sample Analysis SOPIE-1 in February 2022 to image a sample of unknown composition under five wavelengths of light. Through analysis of the SOPIE-1 images, the OSIRIS-REx team identified 6 of the 8 unique lithologies present in the sample. Following SOPIE-1, we conducted further analysis and identified a candidate stone to represent one of the missing lithologies. Conclusion: The successful use of the prototype QRIS in this exercise suggests that a similar system, with a more sophisticated camera, mount, and software, will be sufficient for subsequent SOPIEs and the real Bennu sample selection. The detector, lighting, and optics procured during this project will be key components in producing sciencequality images at the SOPIE-2 in August 2022. [ABSTRACT FROM AUTHOR]

Published
2022

28. Fine-regolith production on asteroids controlled by rock porosity

Author

Cambioni, S., Delbo, M., Poggiali, G., Avdellidou, C., Ryan, A. J., Deshapriya, J. D. P., Asphaug, E., Ballouz, R.-L., Barucci, M. A., Bennett, C. A., Bottke, W. F., Brucato, J. R., Burke, K. N., Cloutis, E., DellaGiustina, D. N., Emery, J. P., Rozitis, B., Walsh, K. J., Lauretta, D. S., Cambioni, S., Delbo, M., Poggiali, G., Avdellidou, C., Ryan, A. J., Deshapriya, J. D. P., Asphaug, E., Ballouz, R.-L., Barucci, M. A., Bennett, C. A., Bottke, W. F., Brucato, J. R., Burke, K. N., Cloutis, E., DellaGiustina, D. N., Emery, J. P., Rozitis, B., Walsh, K. J., and Lauretta, D. S.

Abstract

Spacecraft missions have observed regolith blankets of unconsolidated subcentimetre particles on stony asteroids. Telescopic data have suggested the presence of regolith blankets also on carbonaceous asteroids, including (101955) Bennu and (162173) Ryugu. However, despite observations of processes that are capable of comminuting boulders into unconsolidated materials, such as meteoroid bombardment and thermal cracking, Bennu and Ryugu lack extensive areas covered in subcentimetre particles. Here we report an inverse correlation between the local abundance of subcentimetre particles and the porosity of rocks on Bennu. We interpret this finding to mean that accumulation of unconsolidated subcentimetre particles is frustrated where the rocks are highly porous, which appears to be most of the surface. The highly porous rocks are compressed rather than fragmented by meteoroid impacts, consistent with laboratory experiments, and thermal cracking proceeds more slowly than in denser rocks. We infer that regolith blankets are uncommon on carbonaceous asteroids, which are the most numerous type of asteroid. By contrast, these terrains should be common on stony asteroids, which have less porous rocks and are the second-most populous group by composition. The higher porosity of carbonaceous asteroid materials may have aided in their compaction and cementation to form breccias, which dominate the carbonaceous chondrite meteorites.

29. Regional Photometric Modeling of Asteroid (101955) Bennu

Author

Golish, D. R., Li, J.-Y., Clark, B. E., DellaGiustina, D. N., Zou, X.-D., Rizos, J. L., Hasselmann, P. H., Bennett, C. A., Fornasier, S., Drouet d’Aubigny, C., Rizk, B., Daly, M. G., Barnouin, O. S., Seabrook, J. A., Philpott, L., Al Asad, M. M., Johnson, C. L., Rozitis, B., Ryan, A. J., Emery, J. P., Lauretta, D. S., Golish, D. R., Li, J.-Y., Clark, B. E., DellaGiustina, D. N., Zou, X.-D., Rizos, J. L., Hasselmann, P. H., Bennett, C. A., Fornasier, S., Drouet d’Aubigny, C., Rizk, B., Daly, M. G., Barnouin, O. S., Seabrook, J. A., Philpott, L., Al Asad, M. M., Johnson, C. L., Rozitis, B., Ryan, A. J., Emery, J. P., and Lauretta, D. S.

Abstract

We present a regional photometric analysis of asteroid (101955) Bennu, using image data from the MapCam color imager of the OSIRIS-REx Camera Suite (OCAMS). This analysis follows the previously reported global photometric analysis of Bennu, which found that Bennu’s roughness was difficult to photometrically model owing to unresolved surface variation. Here we find that, even with a high-resolution shape model (20 cm per facet) and automatic image registration (<1 pixel error), Bennu remains a challenging surface to photometrically model: neither a suite of empirical photometric models nor the physically motivated Hapke model were able to eliminate the scatter in the data due to pixel-scale variations. Nonetheless, the models improved on the global analysis by identifying regional variations in Bennu’s photometric response. A linear empirical model, when compared with independent measures of surface roughness and albedo, revealed correlations between those characteristics and phase slope. A regional Hapke analysis showed the same structure in its single-scattering albedo and asymmetry factors; although the Hapke parameters were loosely constrained, complicating interpretation of their spatial variation, the regional variation in relative parameter sensitivity also correlated with shallower phase slope, higher albedo, and less macroscopic roughness.

30. Variations in color and reflectance on the surface of asteroid (101955) Bennu

Author

DellaGiustina, D. N., Burke, K. N., Walsh, K. J., Smith, P. H., Golish, D. R., Bierhaus, E. B., Ballouz, R.-L., Becker, T. L., Campins, H., Tatsumi, E., Yumoto, K., Sugita, S., Deshapriya, J. D. Prasanna, Cloutis, E. A., Clark, B. E., Hendrix, A. R., Sen, A., Al Asad, M. M., Daly, M. G., Applin, D. M., Avdellidou, C., Barucci, M. A., Becker, K. J., Bennett, C. A., Bottke, W. F., Brodbeck, J. I., Connolly, H. C., Delbo, M., de Leon, J., Drouet d’Aubigny, C. Y., Edmundson, K. L., Fornasier, S., Hamilton, V. E., Hasselmann, P. H., Hergenrother, C. W., Howell, E. S., Jawin, E. R., Kaplan, H. H., Le Corre, L., Lim, L. F., Li, J. Y., Michel, P., Molaro, J. L., Nolan, M. C., Nolau, J., Pajola, M., Parkinson, A., Popescu, M., Porter, N. A., Rizk, B., Rizos, J. L., Ryan, A. J., Rozitis, B., Shultz, N. K., Simon, A. A., Trang, D., Van Auken, R. B., Wolner, C. W. V., Lauretta, D. S., DellaGiustina, D. N., Burke, K. N., Walsh, K. J., Smith, P. H., Golish, D. R., Bierhaus, E. B., Ballouz, R.-L., Becker, T. L., Campins, H., Tatsumi, E., Yumoto, K., Sugita, S., Deshapriya, J. D. Prasanna, Cloutis, E. A., Clark, B. E., Hendrix, A. R., Sen, A., Al Asad, M. M., Daly, M. G., Applin, D. M., Avdellidou, C., Barucci, M. A., Becker, K. J., Bennett, C. A., Bottke, W. F., Brodbeck, J. I., Connolly, H. C., Delbo, M., de Leon, J., Drouet d’Aubigny, C. Y., Edmundson, K. L., Fornasier, S., Hamilton, V. E., Hasselmann, P. H., Hergenrother, C. W., Howell, E. S., Jawin, E. R., Kaplan, H. H., Le Corre, L., Lim, L. F., Li, J. Y., Michel, P., Molaro, J. L., Nolan, M. C., Nolau, J., Pajola, M., Parkinson, A., Popescu, M., Porter, N. A., Rizk, B., Rizos, J. L., Ryan, A. J., Rozitis, B., Shultz, N. K., Simon, A. A., Trang, D., Van Auken, R. B., Wolner, C. W. V., and Lauretta, D. S.

Abstract

Visible-wavelength color and reflectance provide information about the geologic history of planetary surfaces. We present multispectral images (0.44 to 0.89 microns) of near-Earth asteroid (101955) Bennu. The surface has variable colors overlain on a moderately blue global terrain. Two primary boulder types are distinguishable by their reflectance and texture. Space weathering of Bennu surface materials does not simply progress from red to blue (or vice versa). Instead, freshly exposed, redder surfaces initially brighten in the near-ultraviolet (become bluer at shorter wavelengths), then brighten in the visible to near-infrared, leading to Bennu’s moderately blue average color. Craters indicate that the timescale of these color changes is ~105 years. We attribute the reflectance and color variation to a combination of primordial heterogeneity and varying exposure ages.

31. Asteroid (101955) Bennu’s weak boulders and thermally anomalous equator

Author

Rozitis, B., Ryan, A. J., Emery, J. P., Christensen, P. R., Hamilton, V. E., Simon, A. A., Reuter, D. C., Al Asad, M., Ballouz, R.-L., Bandfield, J. L., Barnouin, O. S., Bennett, C. A., Bernacki, M., Burke, K. N., Cambioni, S., Clark, B. E., Daly, M. G., Delbo, M., DellaGiustina, D. N., Elder, C. M., Hanna, R. D., Haberle, C. W., Howell, E. S., Golish, D. R., Jawin, E. R., Kaplan, H. H., Lim, L. F., Molaro, J. L., Munoz, D. Pino, Nolan, M. C., Rizk, B., Siegler, M. A., Susorney, H. C. M., Walsh, K. J., Lauretta, D. S., Rozitis, B., Ryan, A. J., Emery, J. P., Christensen, P. R., Hamilton, V. E., Simon, A. A., Reuter, D. C., Al Asad, M., Ballouz, R.-L., Bandfield, J. L., Barnouin, O. S., Bennett, C. A., Bernacki, M., Burke, K. N., Cambioni, S., Clark, B. E., Daly, M. G., Delbo, M., DellaGiustina, D. N., Elder, C. M., Hanna, R. D., Haberle, C. W., Howell, E. S., Golish, D. R., Jawin, E. R., Kaplan, H. H., Lim, L. F., Molaro, J. L., Munoz, D. Pino, Nolan, M. C., Rizk, B., Siegler, M. A., Susorney, H. C. M., Walsh, K. J., and Lauretta, D. S.

Abstract

Thermal inertia and surface roughness are proxies for the physical characteristics of planetary surfaces. Global maps of these two properties distinguish the boulder population on near-Earth asteroid (NEA) (101955) Bennu into two types that differ in strength, and both have lower thermal inertia than expected for boulders and meteorites. Neither has strongly temperature-dependent thermal properties. The weaker boulder type probably would not survive atmospheric entry and thus may not be represented in the meteorite collection. The maps also show a high–thermal inertia band at Bennu’s equator, which might be explained by processes such as compaction or strength sorting during mass movement, but these explanations are not wholly consistent with other data. Our findings imply that other C-complex NEAs likely have boulders similar to those on Bennu rather than finer-particulate regoliths. A tentative correlation between albedo and thermal inertia of C-complex NEAs may be due to relative abundances of boulder types.

32. Episodes of particle ejection from the surface of the active asteroid (101955) Bennu

Author

Lauretta, D. S., Hergenrother, C. W., Chesley, S. R., Leonard, J. M., Pelgrift, J. Y., Adam, C. D., Al Asad, M., Antreasian, P. G., Ballouz, R.-L., Becker, K. J., Bennett, C. A., Bos, B. J., Bottke, W. F., Brozovic, M., Campins, H., Connolly Jr., H. C., Daly, M. G., Davis, A. B., de Leon, J., DellaGiustina, D. N., Drouet d'Aubigny, C. Y., Dworkin, J. P., Emery, J. P., Farnocchia, D., Glavin, D. P., Golish, D. R., Hartzell, C. M., Jacobson, R. A., Jawin, E. R., Jenniskens, P., Kidd Jr., J. N., Lessac-Chenen, E. J., Li, J.-Y., Libourel, G., Licandro, J., Liounis, A. J., Maleszewski, C. K., Manzoni, C., May, B., McCarthy, L. K., McMahon, J., Michel, P., Molaro, J. L., Moreau, M. C., Nelson, D. S., Owen Jr., W. M., Rizk, B., Roper, H. L., Rozitis, B., Sahr, E. M., Scheeres, D. J., Seabrook, J. A., Selznick, S. H., Takahashi, Y., Thuillet, F., Tricarico, P., Vokrouhlicky, D., Wolner, C. W. V., Lauretta, D. S., Hergenrother, C. W., Chesley, S. R., Leonard, J. M., Pelgrift, J. Y., Adam, C. D., Al Asad, M., Antreasian, P. G., Ballouz, R.-L., Becker, K. J., Bennett, C. A., Bos, B. J., Bottke, W. F., Brozovic, M., Campins, H., Connolly Jr., H. C., Daly, M. G., Davis, A. B., de Leon, J., DellaGiustina, D. N., Drouet d'Aubigny, C. Y., Dworkin, J. P., Emery, J. P., Farnocchia, D., Glavin, D. P., Golish, D. R., Hartzell, C. M., Jacobson, R. A., Jawin, E. R., Jenniskens, P., Kidd Jr., J. N., Lessac-Chenen, E. J., Li, J.-Y., Libourel, G., Licandro, J., Liounis, A. J., Maleszewski, C. K., Manzoni, C., May, B., McCarthy, L. K., McMahon, J., Michel, P., Molaro, J. L., Moreau, M. C., Nelson, D. S., Owen Jr., W. M., Rizk, B., Roper, H. L., Rozitis, B., Sahr, E. M., Scheeres, D. J., Seabrook, J. A., Selznick, S. H., Takahashi, Y., Thuillet, F., Tricarico, P., Vokrouhlicky, D., and Wolner, C. W. V.

Abstract

Active asteroids are those that show evidence of ongoing mass loss. We report repeated instances of particle ejection from the surface of (101955) Bennu, demonstrating that it is an active asteroid. The ejection events were imaged by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) spacecraft. For the three largest events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. We also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the Bennu environment. We consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteroid impacts, thermal stress fracturing, and secondary impacts.

33. Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis

Author

DellaGiustina, D. N., Emery, J. P., Golish, D. R., Rozitis, Benjamin, Bennett, C. A., Burke, K. N., Ballouz, R.-L., Becker, K. J., Christensen, P. R., Drouet d’Aubigny, C. Y., Hamilton, V. E., Reuter, D. C., Rizk, B., Simon, A. A., Asphaug, E., Bandfield, J. L., Barnouin, O. S., Barucci, M. A., Bierhaus, E. B., Binzel, R. P., Bottke, W. F., Bowles, N. E., Campins, H., Clark, B. C., Clark, B. E., Connolly, H. C., Daly, M. G., Leon, J. de, Delbo’, M., Deshapriya, J. D. P., Elder, C. M., Fornasier, S., Hergenrother, C. W., Howell, E. S., Jawin, E. R., Kaplan, H. H., Kareta, T. R., Le Corre, L., Li, J.-Y., Licandro, J., Lim, L. F., Michel, P., Molaro, J., Nolan, M. C., Pajola, M., Popescu, M., Garcia, J. L. Rizos, Ryan, A., Schwartz, S. R., Shultz, N., Siegler, M. A., Smith, P. H., Tatsumi, E., Thomas, C. A., Walsh, K. J., Wolner, C. W. V., Zou, X.-D., Lauretta, D. S., DellaGiustina, D. N., Emery, J. P., Golish, D. R., Rozitis, Benjamin, Bennett, C. A., Burke, K. N., Ballouz, R.-L., Becker, K. J., Christensen, P. R., Drouet d’Aubigny, C. Y., Hamilton, V. E., Reuter, D. C., Rizk, B., Simon, A. A., Asphaug, E., Bandfield, J. L., Barnouin, O. S., Barucci, M. A., Bierhaus, E. B., Binzel, R. P., Bottke, W. F., Bowles, N. E., Campins, H., Clark, B. C., Clark, B. E., Connolly, H. C., Daly, M. G., Leon, J. de, Delbo’, M., Deshapriya, J. D. P., Elder, C. M., Fornasier, S., Hergenrother, C. W., Howell, E. S., Jawin, E. R., Kaplan, H. H., Kareta, T. R., Le Corre, L., Li, J.-Y., Licandro, J., Lim, L. F., Michel, P., Molaro, J., Nolan, M. C., Pajola, M., Popescu, M., Garcia, J. L. Rizos, Ryan, A., Schwartz, S. R., Shultz, N., Siegler, M. A., Smith, P. H., Tatsumi, E., Thomas, C. A., Walsh, K. J., Wolner, C. W. V., Zou, X.-D., and Lauretta, D. S.

Abstract

Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennu’s surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennu’s moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennu’s surface particles span from the disruption of the asteroid’s parent body (boulders) to recent in situ production (micrometre-scale particles).

34. Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis

Author

DellaGiustina, D. N., Emery, J. P., Golish, D. R., Rozitis, Benjamin, Bennett, C. A., Burke, K. N., Ballouz, R.-L., Becker, K. J., Christensen, P. R., Drouet d’Aubigny, C. Y., Hamilton, V. E., Reuter, D. C., Rizk, B., Simon, A. A., Asphaug, E., Bandfield, J. L., Barnouin, O. S., Barucci, M. A., Bierhaus, E. B., Binzel, R. P., Bottke, W. F., Bowles, N. E., Campins, H., Clark, B. C., Clark, B. E., Connolly, H. C., Daly, M. G., Leon, J. de, Delbo’, M., Deshapriya, J. D. P., Elder, C. M., Fornasier, S., Hergenrother, C. W., Howell, E. S., Jawin, E. R., Kaplan, H. H., Kareta, T. R., Le Corre, L., Li, J.-Y., Licandro, J., Lim, L. F., Michel, P., Molaro, J., Nolan, M. C., Pajola, M., Popescu, M., Garcia, J. L. Rizos, Ryan, A., Schwartz, S. R., Shultz, N., Siegler, M. A., Smith, P. H., Tatsumi, E., Thomas, C. A., Walsh, K. J., Wolner, C. W. V., Zou, X.-D., Lauretta, D. S., DellaGiustina, D. N., Emery, J. P., Golish, D. R., Rozitis, Benjamin, Bennett, C. A., Burke, K. N., Ballouz, R.-L., Becker, K. J., Christensen, P. R., Drouet d’Aubigny, C. Y., Hamilton, V. E., Reuter, D. C., Rizk, B., Simon, A. A., Asphaug, E., Bandfield, J. L., Barnouin, O. S., Barucci, M. A., Bierhaus, E. B., Binzel, R. P., Bottke, W. F., Bowles, N. E., Campins, H., Clark, B. C., Clark, B. E., Connolly, H. C., Daly, M. G., Leon, J. de, Delbo’, M., Deshapriya, J. D. P., Elder, C. M., Fornasier, S., Hergenrother, C. W., Howell, E. S., Jawin, E. R., Kaplan, H. H., Kareta, T. R., Le Corre, L., Li, J.-Y., Licandro, J., Lim, L. F., Michel, P., Molaro, J., Nolan, M. C., Pajola, M., Popescu, M., Garcia, J. L. Rizos, Ryan, A., Schwartz, S. R., Shultz, N., Siegler, M. A., Smith, P. H., Tatsumi, E., Thomas, C. A., Walsh, K. J., Wolner, C. W. V., Zou, X.-D., and Lauretta, D. S.

Abstract

Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennu’s surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennu’s moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennu’s surface particles span from the disruption of the asteroid’s parent body (boulders) to recent in situ production (micrometre-scale particles).

35. Asteroid (101955) Bennu’s weak boulders and thermally anomalous equator

Author

Rozitis, B., Ryan, A. J., Emery, J. P., Christensen, P. R., Hamilton, V. E., Simon, A. A., Reuter, D. C., Al Asad, M., Ballouz, R.-L., Bandfield, J. L., Barnouin, O. S., Bennett, C. A., Bernacki, M., Burke, K. N., Cambioni, S., Clark, B. E., Daly, M. G., Delbo, M., DellaGiustina, D. N., Elder, C. M., Hanna, R. D., Haberle, C. W., Howell, E. S., Golish, D. R., Jawin, E. R., Kaplan, H. H., Lim, L. F., Molaro, J. L., Munoz, D. Pino, Nolan, M. C., Rizk, B., Siegler, M. A., Susorney, H. C. M., Walsh, K. J., Lauretta, D. S., Rozitis, B., Ryan, A. J., Emery, J. P., Christensen, P. R., Hamilton, V. E., Simon, A. A., Reuter, D. C., Al Asad, M., Ballouz, R.-L., Bandfield, J. L., Barnouin, O. S., Bennett, C. A., Bernacki, M., Burke, K. N., Cambioni, S., Clark, B. E., Daly, M. G., Delbo, M., DellaGiustina, D. N., Elder, C. M., Hanna, R. D., Haberle, C. W., Howell, E. S., Golish, D. R., Jawin, E. R., Kaplan, H. H., Lim, L. F., Molaro, J. L., Munoz, D. Pino, Nolan, M. C., Rizk, B., Siegler, M. A., Susorney, H. C. M., Walsh, K. J., and Lauretta, D. S.

Abstract

Thermal inertia and surface roughness are proxies for the physical characteristics of planetary surfaces. Global maps of these two properties distinguish the boulder population on near-Earth asteroid (NEA) (101955) Bennu into two types that differ in strength, and both have lower thermal inertia than expected for boulders and meteorites. Neither has strongly temperature-dependent thermal properties. The weaker boulder type probably would not survive atmospheric entry and thus may not be represented in the meteorite collection. The maps also show a high–thermal inertia band at Bennu’s equator, which might be explained by processes such as compaction or strength sorting during mass movement, but these explanations are not wholly consistent with other data. Our findings imply that other C-complex NEAs likely have boulders similar to those on Bennu rather than finer-particulate regoliths. A tentative correlation between albedo and thermal inertia of C-complex NEAs may be due to relative abundances of boulder types.

36. Variations in color and reflectance on the surface of asteroid (101955) Bennu

Author

DellaGiustina, D. N., Burke, K. N., Walsh, K. J., Smith, P. H., Golish, D. R., Bierhaus, E. B., Ballouz, R.-L., Becker, T. L., Campins, H., Tatsumi, E., Yumoto, K., Sugita, S., Deshapriya, J. D. Prasanna, Cloutis, E. A., Clark, B. E., Hendrix, A. R., Sen, A., Al Asad, M. M., Daly, M. G., Applin, D. M., Avdellidou, C., Barucci, M. A., Becker, K. J., Bennett, C. A., Bottke, W. F., Brodbeck, J. I., Connolly, H. C., Delbo, M., de Leon, J., Drouet d’Aubigny, C. Y., Edmundson, K. L., Fornasier, S., Hamilton, V. E., Hasselmann, P. H., Hergenrother, C. W., Howell, E. S., Jawin, E. R., Kaplan, H. H., Le Corre, L., Lim, L. F., Li, J. Y., Michel, P., Molaro, J. L., Nolan, M. C., Nolau, J., Pajola, M., Parkinson, A., Popescu, M., Porter, N. A., Rizk, B., Rizos, J. L., Ryan, A. J., Rozitis, B., Shultz, N. K., Simon, A. A., Trang, D., Van Auken, R. B., Wolner, C. W. V., Lauretta, D. S., DellaGiustina, D. N., Burke, K. N., Walsh, K. J., Smith, P. H., Golish, D. R., Bierhaus, E. B., Ballouz, R.-L., Becker, T. L., Campins, H., Tatsumi, E., Yumoto, K., Sugita, S., Deshapriya, J. D. Prasanna, Cloutis, E. A., Clark, B. E., Hendrix, A. R., Sen, A., Al Asad, M. M., Daly, M. G., Applin, D. M., Avdellidou, C., Barucci, M. A., Becker, K. J., Bennett, C. A., Bottke, W. F., Brodbeck, J. I., Connolly, H. C., Delbo, M., de Leon, J., Drouet d’Aubigny, C. Y., Edmundson, K. L., Fornasier, S., Hamilton, V. E., Hasselmann, P. H., Hergenrother, C. W., Howell, E. S., Jawin, E. R., Kaplan, H. H., Le Corre, L., Lim, L. F., Li, J. Y., Michel, P., Molaro, J. L., Nolan, M. C., Nolau, J., Pajola, M., Parkinson, A., Popescu, M., Porter, N. A., Rizk, B., Rizos, J. L., Ryan, A. J., Rozitis, B., Shultz, N. K., Simon, A. A., Trang, D., Van Auken, R. B., Wolner, C. W. V., and Lauretta, D. S.

Abstract

Visible-wavelength color and reflectance provide information about the geologic history of planetary surfaces. We present multispectral images (0.44 to 0.89 microns) of near-Earth asteroid (101955) Bennu. The surface has variable colors overlain on a moderately blue global terrain. Two primary boulder types are distinguishable by their reflectance and texture. Space weathering of Bennu surface materials does not simply progress from red to blue (or vice versa). Instead, freshly exposed, redder surfaces initially brighten in the near-ultraviolet (become bluer at shorter wavelengths), then brighten in the visible to near-infrared, leading to Bennu’s moderately blue average color. Craters indicate that the timescale of these color changes is ~105 years. We attribute the reflectance and color variation to a combination of primordial heterogeneity and varying exposure ages.

37. Fine-regolith production on asteroids controlled by rock porosity

Author

Cambioni, S., Delbo, M., Poggiali, G., Avdellidou, C., Ryan, A. J., Deshapriya, J. D. P., Asphaug, E., Ballouz, R.-L., Barucci, M. A., Bennett, C. A., Bottke, W. F., Brucato, J. R., Burke, K. N., Cloutis, E., DellaGiustina, D. N., Emery, J. P., Rozitis, B., Walsh, K. J., Lauretta, D. S., Cambioni, S., Delbo, M., Poggiali, G., Avdellidou, C., Ryan, A. J., Deshapriya, J. D. P., Asphaug, E., Ballouz, R.-L., Barucci, M. A., Bennett, C. A., Bottke, W. F., Brucato, J. R., Burke, K. N., Cloutis, E., DellaGiustina, D. N., Emery, J. P., Rozitis, B., Walsh, K. J., and Lauretta, D. S.

Abstract

Spacecraft missions have observed regolith blankets of unconsolidated subcentimetre particles on stony asteroids. Telescopic data have suggested the presence of regolith blankets also on carbonaceous asteroids, including (101955) Bennu and (162173) Ryugu. However, despite observations of processes that are capable of comminuting boulders into unconsolidated materials, such as meteoroid bombardment and thermal cracking, Bennu and Ryugu lack extensive areas covered in subcentimetre particles. Here we report an inverse correlation between the local abundance of subcentimetre particles and the porosity of rocks on Bennu. We interpret this finding to mean that accumulation of unconsolidated subcentimetre particles is frustrated where the rocks are highly porous, which appears to be most of the surface. The highly porous rocks are compressed rather than fragmented by meteoroid impacts, consistent with laboratory experiments, and thermal cracking proceeds more slowly than in denser rocks. We infer that regolith blankets are uncommon on carbonaceous asteroids, which are the most numerous type of asteroid. By contrast, these terrains should be common on stony asteroids, which have less porous rocks and are the second-most populous group by composition. The higher porosity of carbonaceous asteroid materials may have aided in their compaction and cementation to form breccias, which dominate the carbonaceous chondrite meteorites.

38. Regional Photometric Modeling of Asteroid (101955) Bennu

Author

Golish, D. R., Li, J.-Y., Clark, B. E., DellaGiustina, D. N., Zou, X.-D., Rizos, J. L., Hasselmann, P. H., Bennett, C. A., Fornasier, S., Drouet d’Aubigny, C., Rizk, B., Daly, M. G., Barnouin, O. S., Seabrook, J. A., Philpott, L., Al Asad, M. M., Johnson, C. L., Rozitis, B., Ryan, A. J., Emery, J. P., Lauretta, D. S., Golish, D. R., Li, J.-Y., Clark, B. E., DellaGiustina, D. N., Zou, X.-D., Rizos, J. L., Hasselmann, P. H., Bennett, C. A., Fornasier, S., Drouet d’Aubigny, C., Rizk, B., Daly, M. G., Barnouin, O. S., Seabrook, J. A., Philpott, L., Al Asad, M. M., Johnson, C. L., Rozitis, B., Ryan, A. J., Emery, J. P., and Lauretta, D. S.

Abstract

We present a regional photometric analysis of asteroid (101955) Bennu, using image data from the MapCam color imager of the OSIRIS-REx Camera Suite (OCAMS). This analysis follows the previously reported global photometric analysis of Bennu, which found that Bennu’s roughness was difficult to photometrically model owing to unresolved surface variation. Here we find that, even with a high-resolution shape model (20 cm per facet) and automatic image registration (<1 pixel error), Bennu remains a challenging surface to photometrically model: neither a suite of empirical photometric models nor the physically motivated Hapke model were able to eliminate the scatter in the data due to pixel-scale variations. Nonetheless, the models improved on the global analysis by identifying regional variations in Bennu’s photometric response. A linear empirical model, when compared with independent measures of surface roughness and albedo, revealed correlations between those characteristics and phase slope. A regional Hapke analysis showed the same structure in its single-scattering albedo and asymmetry factors; although the Hapke parameters were loosely constrained, complicating interpretation of their spatial variation, the regional variation in relative parameter sensitivity also correlated with shallower phase slope, higher albedo, and less macroscopic roughness.

39. Episodes of particle ejection from the surface of the active asteroid (101955) Bennu

Author

Lauretta, D. S., Hergenrother, C. W., Chesley, S. R., Leonard, J. M., Pelgrift, J. Y., Adam, C. D., Al Asad, M., Antreasian, P. G., Ballouz, R.-L., Becker, K. J., Bennett, C. A., Bos, B. J., Bottke, W. F., Brozovic, M., Campins, H., Connolly Jr., H. C., Daly, M. G., Davis, A. B., de Leon, J., DellaGiustina, D. N., Drouet d'Aubigny, C. Y., Dworkin, J. P., Emery, J. P., Farnocchia, D., Glavin, D. P., Golish, D. R., Hartzell, C. M., Jacobson, R. A., Jawin, E. R., Jenniskens, P., Kidd Jr., J. N., Lessac-Chenen, E. J., Li, J.-Y., Libourel, G., Licandro, J., Liounis, A. J., Maleszewski, C. K., Manzoni, C., May, B., McCarthy, L. K., McMahon, J., Michel, P., Molaro, J. L., Moreau, M. C., Nelson, D. S., Owen Jr., W. M., Rizk, B., Roper, H. L., Rozitis, B., Sahr, E. M., Scheeres, D. J., Seabrook, J. A., Selznick, S. H., Takahashi, Y., Thuillet, F., Tricarico, P., Vokrouhlicky, D., Wolner, C. W. V., Lauretta, D. S., Hergenrother, C. W., Chesley, S. R., Leonard, J. M., Pelgrift, J. Y., Adam, C. D., Al Asad, M., Antreasian, P. G., Ballouz, R.-L., Becker, K. J., Bennett, C. A., Bos, B. J., Bottke, W. F., Brozovic, M., Campins, H., Connolly Jr., H. C., Daly, M. G., Davis, A. B., de Leon, J., DellaGiustina, D. N., Drouet d'Aubigny, C. Y., Dworkin, J. P., Emery, J. P., Farnocchia, D., Glavin, D. P., Golish, D. R., Hartzell, C. M., Jacobson, R. A., Jawin, E. R., Jenniskens, P., Kidd Jr., J. N., Lessac-Chenen, E. J., Li, J.-Y., Libourel, G., Licandro, J., Liounis, A. J., Maleszewski, C. K., Manzoni, C., May, B., McCarthy, L. K., McMahon, J., Michel, P., Molaro, J. L., Moreau, M. C., Nelson, D. S., Owen Jr., W. M., Rizk, B., Roper, H. L., Rozitis, B., Sahr, E. M., Scheeres, D. J., Seabrook, J. A., Selznick, S. H., Takahashi, Y., Thuillet, F., Tricarico, P., Vokrouhlicky, D., and Wolner, C. W. V.

Abstract

Active asteroids are those that show evidence of ongoing mass loss. We report repeated instances of particle ejection from the surface of (101955) Bennu, demonstrating that it is an active asteroid. The ejection events were imaged by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) spacecraft. For the three largest events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. We also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the Bennu environment. We consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteroid impacts, thermal stress fracturing, and secondary impacts.

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