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1. Sensitivity Testing of Stereophotoclinometry for the OSIRIS-REx Mission. I. The Accuracy and Errors of Digital Terrain Modeling

Author

Eric E. Palmer, John R. Weirich, Robert W. Gaskell, Diane Lambert, Tanner Campbell, Kris Drozd, Olivier S. Barnouin, Michael G. Daly, Kenneth Getzandanner, John N. Kidd Jr., Coralie D. Adam, and Dante S. Lauretta

Subjects
Asteroids, Small Solar System bodies, Near-Earth objects, Astronomy, QB1-991
Abstract

Stereophotoclinometry (SPC) was the prime method of shape modeling for NASA’s OSIRIS-REx mission to asteroid Bennu. Here we describe the extensive testing conducted before launch to certify SPC as NASA Class B flight software, which not only validated SPC for operational use but also quantified the accuracy of this technique. We used a computer-generated digital terrain model (DTM) of a synthetic asteroid as the truth input to render simulated truth images per the planned OSIRIS-REx observing campaign. The truth images were then used as input to SPC to create testing DTMs. Imaging sets, observational parameters, and processing techniques were varied to evaluate their effects on SPC's performance and their relative importance for the quality of the resulting DTMs. We show that the errors in accuracy for SPC models are of the order of the source images’ smallest pixel sizes and that a DTM can be created at any scale, provided there is sufficient imagery at that scale. Uncertainty in the spacecraft’s flight path has minimal impact on the accuracy of SPC models. Subtraction between two DTMs (truth and simulated) is an effective approach for measuring error but has limitations. Comparing the simulated truth images with images rendered from the SPC-derived DTMs provides an excellent metric for DTM quality at smaller scales and can also be applied in flight by using real images of the target. SPC has limitations near steep slopes (e.g., the sides of boulders), leading to height errors of more than 30%. This assessment of the accuracy and sensitivity of SPC provides confidence in this technique and lessons that can be applied to future missions.

Published
2024
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2. Sensitivity Testing of Stereophotoclinometry for the OSIRIS-REx Mission. II. Effective Observation Geometry for Digital Terrain Modeling

Author

Eric E. Palmer, John R. Weirich, Robert W. Gaskell, Diane Lambert, Tanner Campbell, Kris Drozd, Olivier S. Barnouin, Michael G. Daly, Kenneth Getzandanner, John N. Kidd Jr., Coralie D. Adam, and Dante S. Lauretta

Subjects
Asteroid surfaces, Asteroids, Near-Earth objects, Astronomy, QB1-991
Abstract

The OSIRIS-REx mission used stereophotoclinometry (SPC) to generate digital terrain models (DTMs) of its target asteroid, Bennu. Here we present a suite of preflight tests conducted to identify the observing geometry and number of images needed to create DTMs that would enable successful navigation around and to the surface of the asteroid. We demonstrate that high-quality DTMs can be generated by using only five images: four that are focused on topography, in which the spacecraft’s viewing geometry brackets the target (north, south, east, and west), and a fifth that measures the target’s albedo variation, taken from near local noon. We further show that the first 10 iterations of the SPC process can meaningfully improve DTM quality, including in the case of a suboptimal input image set, whereas after 10 iterations the DTM quality approaches an asymptotic maximum. We distill our findings into recommendations for observation planning that can be applied by other missions intending to use SPC to model the shape and terrain of their target.

Published
2024
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3. Stereophotoclinometry for OSIRIS-REx Spacecraft Navigation

Author

Coralie D. Adam, Leilah K. McCarthy, Jason M. Leonard, Robert Gaskell, Peter G. Antreasian, Andrew J. Liounis, Kenneth Getzandanner, Michael C. Moreau, Eric E. Palmer, John Weirich, Olivier S. Barnouin, Jeroen L. Geeraert, Eric M. Sahr, Benjamin Ashman, Derek S. Nelson, John Y. Pelgrift, Erik J. Lessac-Chenen, Daniel Wibben, Bobby G. Williams, Michael G. Daly, and Dante S. Lauretta

Published
2023
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5. OSIRIS-APEX: An OSIRIS-REx Extended Mission to Asteroid Apophis

Author

Daniella N. DellaGiustina, Michael C. Nolan, Anjani T. Polit, Michael C. Moreau, Dathon R. Golish, Amy A. Simon, Coralie D. Adam, Peter G. Antreasian, Ronald-Louis Ballouz, Olivier S. Barnouin, Kris J. Becker, Carina A. Bennett, Richard P. Binzel, Brent J. Bos, Richard Burns, Nayessda Castro, Steven R. Chesley, Philip R. Christensen, M. Katherine Crombie, Michael G. Daly, R. Terik Daly, Heather L. Enos, Davide Farnocchia, Sandra Freund Kasper, Rose Garcia, Kenneth M. Getzandanner, Scott D. Guzewich, Christopher W. Haberle, Timothy Haltigin, Victoria E. Hamilton, Karl Harshman, Noble Hatten, Kyle M. Hughes, Erica R. Jawin, Hannah H. Kaplan, Dante S. Lauretta, Jason M. Leonard, Andrew H. Levine, Andrew J. Liounis, Christian W. May, Laura C. Mayorga, Lillian Nguyen, Lynnae C. Quick, Dennis C. Reuter, Edgard Rivera-Valentín, Bashar Rizk, Heather L. Roper, Andrew J. Ryan, Brian Sutter, Mathilde M. Westermann, Daniel R. Wibben, Bobby G. Williams, Kenneth Williams, and C. W. V. Wolner

Subjects
Asteroid dynamics, Asteroid surfaces, Near-Earth objects, Close encounters, Space observatories, Astronomy, QB1-991
Abstract

The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft mission characterized and collected a sample from asteroid (101955) Bennu. After the OSIRIS-REx Sample Return Capsule released to Earth’s surface in 2023 September, the spacecraft diverted into a new orbit that encounters asteroid (99942) Apophis in 2029, enabling a second mission with the same unique capabilities: OSIRIS–Apophis Explorer (APEX). On 2029 April 13, the 340 m diameter Apophis will draw within ∼32,000 km of Earth’s surface, less than 1/10 the lunar distance. Apophis will be the largest object to approach Earth this closely in recorded history. This rare planetary encounter will alter Apophis’s orbit, will subject it to tidal forces that change its spin state, and may seismically disturb its surface. APEX will distantly observe Apophis during the Earth encounter and capture its evolution in real time, revealing the consequences of an asteroid undergoing tidal disturbance by a major planet. Beginning in 2029 July, the spacecraft’s instrument suite will begin providing high-resolution data of this “stony” asteroid—advancing knowledge of these objects and their connection to meteorites. Near the mission’s end, APEX will use its thrusters to excavate regolith, a technique demonstrated at Bennu. Observations before, during, and after excavation will provide insight into the subsurface and material properties of stony asteroids. Furthermore, Apophis’s material and structure have critical implications for planetary defense.

Published
2023
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6. Contact with Bennu! Flight Performance Versus Prediction of OSIRIS-REx TAG Sample Collection

Author

Kevin E Berry, Kenneth M Getzandanner, Michael C Moreau, Samantha M Rieger, Peter G Antreasian, Coralie D Adam, Daniel R Wibben, Jason M Leonard, Andrew H Levine, Jeroen L Geeraert, John Y Pelgrift, Leilah K McCarthy, Eric M Sahr, David A Lorenz, and Dante S Lauretta

Subjects
Spacecraft Design, Testing And Performance
Abstract

The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission collected a sample from the surface of the near-Earth asteroid (101955) Bennu in late 2020. Bennu challenged the team with a surface that was much rockier than expected, resulting in modifications to the prelaunch design of the Touch And Go (TAG) sequence. Following enhancements in onboard trajectory correction, ground-based navigation, and maneuver execution error modeling, the spacecraft was delivered to the chosen TAG site within 1 m of the target, and a sample was successfully collected on the first attempt. This paper provides a comprehensive description of all flight dynamics aspects of TAG trajectory planning and execution. It also describes hazard map generation and how that combined with error analysis results to predict the probability of safe contact before TAG and the onboard wave-off determination during TAG.

Published
2021

7. OSIRIS-REx Proximity Operations and Navigation Performanceat (101955) Bennu

Author

Peter G. Antreasian, Coralie D. Adam, Jeroen Geeraet, Jason M Leonard, Erik Lessac-Chenen, Andrew Levine, Jim McAdams, Leilah K. McCarthy, Derek Nelson, Brian Page, John Y. Pelgrift, Eric Sahr, Daniel Wibben, Bobby Williams, Kenneth Williams, Kevin Berry, Kenny Getzandanner, Michael Moreau, Samantha Rieger, Benjamin W. Ashman, Dolan E. Highsmith, and Dante Lauretta

Subjects
Lunar And Planetary Science And Exploration, Space Sciences (General)
Abstract

The NASA Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft began close proximity operations at the small (500-m diameter) B-type asteroid (101955) Bennu in December 2018 and concluded in May 2021. Hundreds of grams of pristine surface regolith were collected on October 20, 2020, when the OSIRIS-REx spacecraft successfully executed the Touch and Go (TAG) sample collection sequence. The spacecraft touched down within 1 meter of the targeted site on the surface of Bennu. TAG was the culmination of over 2 years of navigation performance refinement as a result of extraordinary interagency teamwork between the Flight Dynamics System (FDS), science and spacecraft teams while in close proximity to Bennu. This paper will discuss the navigation processes, planning and performance during the proximity operations at Bennu.

Published
2021
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8. Small-Body Proximity Operations & TAG: Navigation Experiences & Lessons Learned from the OSIRIS-REx Mission

Author

Kenneth M. Getzandanner, Kevin E. Berry, Peter G. Antreasian, Jason M. Leonard, Coralie D. Adam, Daniel R. Wibben, Michael C. Moreau, Dolan E. Highsmith, and Dante S. Lauretta

Subjects
Spacecraft Instrumentation And Astrionics, Lunar And Planetary Science And Exploration
Abstract

On October 20th, 2020, the nearly two-year proximity operations campaign for the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx)mission at the near-Earth asteroid (101955) Bennu culminated in a successful Touch-and-Go (TAG) sample collection event. Navigation performance was a significant driver for flight activities at Bennu, which consisted of multiple phases geared towards characterizing the asteroid, selecting a sample site, and safely guiding the spacecraft to and from the surface in order to collect at least 60 g of pristine regolith. The entire operations team gained a tremendous amount of experience operating in the challenging small body environment and overcame many challenges. In this paper, we summarize navigation-focused experiences and lessons learned from OSIRIS-REx proximity operations at Bennu that are applicable to future missions to small asteroids, comets, and planetary moons. Areas of focus include staffing and organization, ground system infrastructure, mission phase planning, navigation operations, and spacecraft and payload considerations.

Published
2021
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9. Concept of Operations for OSIRIS-REx Optical Navigation Image Planning

Author

Coralie D. Adam, Peter G. Antreasian, Brian T. Carcich, Jason M. Leonard, Erik J. Lessac-Chenen, Leilah K. McCarthy, Derek S. Nelson, John Y. Pelgrift, Eric M. Sahr, Daniel R. Wibben, Sara Knutson, Heather L. Enos, Karl Harshman, Carl Hergenrother, John N. Kidd Jr, Diane Lambert, Anjani T. Polit, Bashar Rizk, Dante S. Lauretta, Olivia Billett, Mykal Lefevre, Michael C. Moreau, Brent J. Bos, Andrew Calloway, Nayi Castro, Joseph Cavaluzzi, Kenneth M. Getzandanner, Ronald Mink, and Devin Poland

Subjects
Spacecraft Instrumentation And Astrionics, Lunar And Planetary Science And Exploration
Abstract

Optical navigation (OpNav) is a critical subsystem of the OSIRIS-REx asteroid sample return mission, which operated in the vicinity of near-Earth asteroid (101955) Bennu from August 2018 through April 2021. A substantial amount of mission resources across multiple subsystems and institutions is required to ensure that the OpNav data are successfully acquired. The KinetX OpNav team, part of the Flight Dynamics System (FDS), is responsible for performing required analysis to develop the OpNav operations plans; requesting, reviewing and verifying the plans; and ultimately using the image data for critical navigation operations. The FDS team, responsible for the mission navigation, is operated by KinetX Aerospace with management and operations support from NASA’s Goddard Space Flight Center. The Science Processing and Operations Center (SPOC), located at the University of Arizona’s Lunar and Planetary Laboratory, is responsible for generating the planning products for all science and most OpNav data. These plans are integrated into the spacecraft sequences, tested, and commanded by the Mission Support Area (MSA) at Lockheed Martin Space. To ensure mission-critical navigation image data are successfully acquired, the plan is developed through a waterfall of planning cycles over the course of 3 months prior to onboard plan execution. During the initial strategic planning for a mission phase, detailed analysis is performed by the OpNav team to conceptualize the concept of operations (ConOps) for image data collection. This phase OpNav Narrative is included along with other strategic planning documents for the key ground segment stakeholders to review and provide feedback. The detailed OpNav plans get defined in the tactical planning cycle, which spans 8 to 3 weeks before the week-long integrated sequence is executed on-board the spacecraft. During the tactical cycle, the initial OpNav Request is submitted along with the science requests, kicking off development of the science and OpNav plans. Once the initial plan is drafted, interfaces are exercised so that the plan can be reviewed and iterated, if necessary. A rigorous schedule is followed by the planning teams during the implementation cycle, spanning the last 18 days before uplink, to ensure all the necessary integration, testing, and reviewing can occur on time. The development of the OpNav planning ConOps, including responsibilities, interfaces, timelines, and procedures, took extensive collaboration across mission elements and institutions. The process was robust throughout the 137 weeks of continuous Optical Navigation Operations at Bennu, which concluded on April 9th, 2021.

Published
2021
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10. Navigation Prediction Performance During OSIRIS-REx Proximity Operations at (101955) Bennu

Author

Jason M. Leonard, Jeroen L. Geeraert, John Y. Pelgrift, Peter G. Antreasian, Coralie D. Adam, Daniel R. Wibben, Kenneth M. Getzandanner, Benjamin W. Ashman, and Dante S. Lauretta

Subjects
Spacecraft Instrumentation And Astrionics, Lunar And Planetary Science And Exploration
Abstract

The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification and Security–Regolith Explorer) Orbit Determination team performed covariance analyses prior to the commencement of proximity operations (ProxOps) at (101955) Bennu to determine the expected predicted trajectory performance in order to meet trajectory knowledge requirements throughout each phase of the mission. One of the primary requirements placed on the predicted trajectory performance was based on the performance during orbital phases leading up to the maneuver to initiate the Touch-and-Go (TAG) trajectory descent. Throughout ProxOps the nominal force models being used to predict the spacecraft trajectory were updated in an effort to improve the prediction performance. The most significant models that contributed to prediction performance were of solar radiation pressure, thermal reradiation of the spacecraft, predicted attitude errors, and desaturation maneuvers. Efforts were made throughout all of ProxOps to monitor, trend, predict, and update spacecraft modeling to improve the prediction performance. These efforts were vital to reduce the spacecraft knowledge errors necessary to achieve a TAG target smaller than pre-launch analysis allowed due to the rough terrain of Bennu. Increased precision in predicted trajectory errors allowed for refined uncertainties to be used for future phase planning throughout the mission. The navigation team successfully predicted the spacecraft trajectory throughout all of ProxOps achieving predicted trajectories errors less than originally analyzed.

Published
2021
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11. Reconstruction of Bennu Particle Events From Sparse Data

Author

John Y. Pelgrift, Erik J. Lessac‐Chenen, Coralie D. Adam, Jason M. Leonard, Derek S. Nelson, Leilah McCarthy, Eric M. Sahr, Andrew Liounis, Michael Moreau, Brent J. Bos, Carl W. Hergenrother, and Dante S. Lauretta

Subjects
Astronomy, QB1-991, Geology, QE1-996.5
Abstract

Abstract OSIRIS‐REx began observing particle ejection events shortly after entering orbit around near‐Earth asteroid (101955) Bennu in January 2019. For some of these events, the only observations of the ejected particles come from the first two images taken immediately after the event by OSIRIS‐REx's NavCam 1 imager. Without three or more observations of each particle, traditional orbit determination is not possible. However, by assuming that the particles all ejected at the same time and location for a given event, and approximating that their velocities remained constant after ejection (a reasonable approximation for fast‐moving particles, i.e., with velocities on the order of 10 cm/s or greater, given Bennu's weak gravity), we show that it is possible to estimate the particles' states from only two observations each. We applied this newly developed technique to reconstruct the particle ejection events observed by the OSIRIS‐REx spacecraft during orbit about Bennu. Particles were estimated to have ejected with inertial velocities ranging from 7 cm/s to 3.3 m/s, leading to a variety of trajectory types. Most (>80%) of the analyzed events were estimated to have originated from midlatitude regions and to have occurred after noon (local solar time), between 12:44 and 18:52. Comparison with higher‐fidelity orbit determination solutions for the events with sufficient observations demonstrates the validity of our approach and also sheds light on its biases. Our technique offers the capacity to meaningfully constrain the properties of particle ejection events from limited data.

Published
2020
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12. Autonomous Detection of Particles and Tracks in Optical Images

Author

Andrew J. Liounis, Jeffrey L. Small, Jason C. Swenson, Joshua R. Lyzhoft, Benjamin W. Ashman, Kenneth M. Getzandanner, Michael C. Moreau, Coralie D. Adam, Jason M. Leonard, Derek S. Nelson, John Y. Pelgrift, Brent J. Bos, Steven R. Chesley, Carl W. Hergenrother, and Dante S. Lauretta

Subjects
active asteroid, particle tracking, particle detection, image processing, Astronomy, QB1-991, Geology, QE1-996.5
Abstract

Abstract When optical navigation images acquired by the OSIRIS‐REx (Origins, Spectral Interpretation, Resource Identification, and Security‐Regolith Explorer) mission revealed the periodic ejection of particles from asteroid (101955) Bennu, it became a mission priority to quickly identify and track these objects for both spacecraft safety and scientific purposes. The large number of particles and the mission criticality rendered time‐intensive manual inspection impractical. We present autonomous techniques for particle detection and tracking that were developed in response to the Bennu phenomenon but that have the capacity for general application to particles in motion about a celestial body. In an example OSIRIS‐REx data set, our autonomous techniques identified 93.6% of real particle tracks and nearly doubled the number of tracks detected versus manual inspection alone.

Published
2020
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19. Optical Navigation Preparations for the New Horizons Kuiper-Belt Extended Mission

Author

Mark E. Holdridge, Coralie D. Adam, John R. Spencer, Harold A. Weaver, J. Y. Pelgrift, E. J. Lessac-Chenen, Catherine B. Olkin, Frederic Pelletier, Derek S. Nelson, and S. Alan Stern

Subjects
020301 aerospace & aeronautics, Brightness, Schedule, Spacecraft, business.industry, Computer science, Aerospace Engineering, Image processing, 02 engineering and technology, Astrometry, 01 natural sciences, Pluto, 0203 mechanical engineering, Space and Planetary Science, 0103 physical sciences, Systems design, Aerospace engineering, business, Orbit determination, 010303 astronomy & astrophysics
Abstract

Acquiring and processing astrometric measurements of a spacecraft’s target using on-board images, generically referred to as optical navigation, is an integral function of the orbit determination and navigation of NASA’s New Horizons spacecraft. Since New Horizons’ reconnaissance of the Pluto system in July 2015, many preparations have been completed to further enhance the optical navigation system and prepare for the reconnaissance of New Horizons’ next target, Kuiper Belt Object (486958) 2014 MU69 (unofficially nicknamed Ultima Thule). Due to its low relative brightness compared to most planetary exploration targets, Ultima Thule presents several unique challenges to the optical navigation system. The optical navigation system design, imaging schedule, and technical algorithms that were developed and tailored to these challenges are explored in detail. Additionally, several operational readiness tests, simulation methods, and test results are presented and analyzed to assess the optical navigation system performance and implications to flight operations. Lastly, a first look at Ultima as viewed from the New Horizons LORRI imager is presented.

Published
2019
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20. Quality Assessment of Stereophotoclinometry as a Shape Modeling Method Using a Synthetic Asteroid

Author

John Weirich, Eric E. Palmer, Michael G. Daly, Olivier S. Barnouin, Kenneth Getzandanner, John N. Kidd, Coralie D. Adam, Robert Gaskell, and Dante S. Lauretta

Subjects
Geophysics, Space and Planetary Science, Earth and Planetary Sciences (miscellaneous), Astronomy and Astrophysics
Abstract

The stereophotoclinometry (SPC) software suite has been used to generate global digital terrain models (DTMs) of many asteroids and moons, and was the primary tool used by the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission to model the shape of asteroid Bennu. We describe the dedicated preflight testing of SPC for the OSIRIS-REx mission using a synthetic “truth” asteroid model. SPC has metrics that determine the internal consistency of a DTM, but it was not known how these metrics are related to the absolute accuracy of a DTM, which was important for the operational needs of the mission. The absolute accuracy of an SPC-generated DTM cannot be determined without knowing the truth topography. Consequently, we developed a realistic, but synthetic, computer-generated representation of asteroid Bennu, photographed this synthetic truth model in an imaging campaign similar to that planned for the OSIRIS-REx mission, and then generated a global SPC DTM from these images. We compared the SPC DTM, which was represented by a radius every 70 cm across the asteroid surface, to the synthetic truth model to assess the absolute accuracy. We found that the internal consistency can be used to determine the 3D root-mean-square accuracy of the model to within a factor of two of the absolute accuracy.

Published
2022
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21. Practical Stereophotoclinometry for Modeling Shape and Topography on Planetary Missions

Author

Eric E. Palmer, Robert Gaskell, Michael G. Daly, Olivier S. Barnouin, Coralie D. Adam, and Dante S. Lauretta

Subjects
Geophysics, Space and Planetary Science, Earth and Planetary Sciences (miscellaneous), Astronomy and Astrophysics
Abstract

Stereophotoclinometry (SPC) is a technique to extract topographic information from images acquired by spacecraft. It combines stereophotogrammetry and photoclinometry to produce a product that has the accuracy of stereo with the resolution of photoclinometry without the restrictions common to both. We describe the implementation of this technique in the context of digital terrain model (DTM) generation for a small-body mission. We detail the process and the data used to generate SPC-derived DTMs at progressively increasing resolutions. The highest-quality DTMs are generated using four images optimized for topography, a 30° emission angle with the emission azimuth (spacecraft position) to the north, east, south, and west of the target, and one image optimized for albedo (a low incidence angle such that most of the image pixels’ digital numbers are based upon albedo rather than topography). We discuss implications for mission planning and how SPC-based DTM generation can support spacecraft navigation. As a case study, we share outcomes from the modeling performed for the OSIRIS-REx mission to asteroid Bennu.

Published
2022
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22. Author Correction: Shape of (101955) Bennu indicative of a rubble pile with internal stiffness

Author

M. Lefevre, Aaron S. Burton, Carina Bennett, J. A. Mapel, Renu Malhotra, Peter Fleming, J. McAdams, N. Mogk, R. L. Ballouz, P. H. Smith, V. Nifo, C. K. Maleszewski, Timothy D. Swindle, E. Dotto, Stephen R. Schwartz, C. May, J. Bayron, D. Patterson, D. Guevel, Ellen S. Howell, Humberto Campins, J. Kissell, E. Brown, J. Wood, E. Muhle, John Robert Brucato, J. Small, B. Miller, Oleksiy Golubov, R. Pennington, K. Harshman, J. Nelson, Catherine Elder, M. McGee, R. Burns, J. Contreras, S. Hull, D. Kubitschek, D. Noss, Andrew J. Liounis, J. Backer, B. May, G. Fitzgibbon, J. Donaldson, D. Worden, Bashar Rizk, R. Witherspoon, Catherine L. Johnson, Erica Jawin, G. Shaw, A. Aqueche, Dolores H. Hill, D. Folta, S. Ferrone, M. Lujan, Giovanni Poggiali, B. G. Williams, S. Selznick, Melissa A. Morris, K. Rios, Sara S. Russell, D. Lambert, J. Hong, Jeffrey B. Plescia, H. Bloomenthal, D. Drinnon, Olivier S. Barnouin, Derek S. Nelson, Amanda E. Toland, Michael C. Moreau, J. A. Seabrook, K. Dill, A. Mirfakhrai, K. Hyde, J. D. P. Deshapriya, Hannah Kaplan, Timothy P. McElrath, Juliette I. Brodbeck, N. Ramos, S. Stewart, James B. Garvin, Sei-ichiro Watanabe, M. Arvizu-Jakubicki, Jason P. Dworkin, Matthew A. Siegler, Collin Lewin, Masatoshi Hirabayashi, L. Bloomquist, S. Gardner, Keiko Nakamura-Messenger, A. H. Nair, M. Schmitzer, P. Haas, Julie Bellerose, Dolan E. Highsmith, L. Koelbel, C. C. Lorentson, J. Zareski, E. Queen, S. R. Chesley, Philip A. Bland, A. Cheuvront, V. E. Hamilton, Ronald G. Mink, N. Mastrodemos, H. C. Connolly, K. Bellamy, M. Killgore, A. Gardner, Y. Takahashi, M. Lambert, R. C. Espiritu, Z. Zeszut, E. T. Morton, Kevin J. Walsh, Timothy D. Glotch, M. Skeen, Brian Kennedy, Matthew R.M. Izawa, G. Neumann, F. Teti, D. Doerres, A. Hasten, F. Ciceri, D. Howell, A. Deguzman, J. Nagy, D. Vaughan, H. Ma, C. Lantz, D. N. Brack, David K. Hammond, Erwan Mazarico, Leilah K. McCarthy, L. Rhoads, Kathleen L. Craft, C. Welch, Jay W. McMahon, C. L. Parish, D. C. Reuter, M. Giuntini, N. Castro, Clive Dickinson, J. Kreiner, K. Kingsbury, S. Dickenshied, Joseph A. Nuth, Alan R. Hildebrand, Erik Asphaug, H. Ido, Eric M. Sahr, A. Harbison, Arlin E. Bartels, T. Forrester, D. Eckart, R. Bandrowski, Michael K. Barker, Robert Gaskell, J. Wendel, S. Freund, Marc Bernacki, Ryan S. Park, A. Taylor, E. B. Bierhaus, S. Millington-Veloza, J. Stromberg, L. B. Breitenfeld, K. Stakkestad, D. Ellis, Timothy J. McCoy, M. Susak, Richard G. Cosentino, C. Manzoni, Hisayoshi Yurimoto, C. Drouet d'Aubigny, A. Bjurstrom, Masako Yoshikawa, S. Francis, J. Peachey, J. Geeraert, K. Marchese, O. Billett, M. Rascon, F. Jaen, B. Diallo, Martin Miner, Kris J. Becker, E. Mazzotta Epifani, Florian Thuillet, A. Knight, James H. Roberts, Pasquale Tricarico, Edward A. Cloutis, T. Fisher, Dale Stanbridge, A. Colpo, Osiris-Rex Team, S. Gonzales, Q. Tran, M. K. Crombie, John Marshall, N. Bojorquez-Murphy, David Vokrouhlický, Allen W. Lunsford, H. Bowles, K. L. Edmundson, R. A. Masterson, Peter G. Antreasian, N. Gorius, Benjamin Rozitis, D. Pino Muñoz, S. Carlson-Kelly, C. Thayer, J. Elsila Cook, B. C. Clark, N. Piacentine, José C. Aponte, M. Al Asad, M. A. Barucci, D. Blum, P. Falkenstern, Neil Bowles, Matthew Chojnacki, J. M. Leonard, J. Daly, K. Yetter, M. R. Fisher, Jeffrey N. Grossman, A. Boggs, N. Jayakody, Cristina A. Thomas, C.M. Ernst, Namrah Habib, J. N. Kidd, R. J. Steele, Andrew B. Calloway, Andrew Ryan, Kimberly T. Tait, Paul O. Hayne, J. Y. Li, K. L. Berry, William V. Boynton, Yanga R. Fernandez, D. A. Lorenz, M. Wasser, Daniel J. Scheeres, K. Fortney, A. Scroggins, B. Allen, B. Sutter, T. Ferro, Jonathan Joseph, Derek C. Richardson, D. Hoak, Brian Carcich, W. Chang, P. Wren, C. Boyles, Kaj E. Williams, B. Marty, J. Liang, J. Hoffman, A. Harch, Daniel R. Wibben, Jamie Molaro, S. Rieger, R. Enos, C. W. Hergenrother, Stephen R. Sutton, J. Grindlay, E. J. Lessac-Chenen, E. Huettner, C. Norman, P. Sherman, L. Swanson, M. Coltrin, S. Van wal, B. Buck, A. Fisher, Kevin Righter, Brian Rush, David D. Rowlands, Lauren McGraw, A. Levine, K. Drozd, D. Gaudreau, A. Nguyen, S. Sides, M. Chodas, R. Dubisher, B. Ashman, Michael Caplinger, Amy Simon, W. Moore, S. S. Balram-Knutson, R. Carpenter, S. Fornasier, Shogo Tachibana, Russell Turner, Ian A. Franchi, Trevor Ireland, Chloe B. Beddingfield, D. F. Everett, M. Corvin, Lindsay P. Keller, Tammy L. Becker, S. Carter, J. L. Rizos Garcia, Mark E. Perry, E. Keates, Michael C. Nolan, P. Vasudeva, C. Fellows, K. Herzog, Mark A. Jenkins, J. R. Weirich, J. Swenson, D. R. Golish, Davide Farnocchia, Lydia C. Philpott, Rebecca R. Ghent, Hannah C.M. Susorney, S. W. Squyres, Pedro Hasselmann, J. Hill, Thomas J. Zega, B. Key, Marco Delbo, A. S. French, P. Sánchez, A. Hilbert, J. Y. Pelgrift, R. P. Binzel, L. McNamara, Vishnu Reddy, Michael Daly, Scott Messenger, Daniella DellaGiustina, Maurizio Pajola, Charles Brunet, Joshua L. Bandfield, J. Padilla, A. Janakus, M. Moreau, R. Garcia, R. A. Chicoine, P. Michel, P. Kaotira, K. S. Johnson, J. Forelli, G. Miller, K. Martin, I. Galinsky, S. Desjardins, Naru Hirata, Christine Hartzell, M. L. Jones, S. Hooven, D. Velez, R. Munoz, Carolyn M. Ernst, C. Emr, N. Martinez-Vlasoff, S. Bendall, R. Zellar, E. Church, Theodore Kareta, T. Warren, P. Wolff, V. Morrison, C. Bryan, S. Bhaskaran, N. Jones, D. Hauf, Jeremy Bauman, R. T. Daly, R. Olds, M. M. Westermann, D. K. Hamara, E. Audi, G. Johnston, Eric Palmer, Courtney Mario, Daniel P. Glavin, T. Haltigin, J. Cutts, Javier Licandro, Xiao-Duan Zou, H. L. Roper, Gregory A. Neumann, William M. Owen, S. Sugita, Y. H. Tang, Kevin Burke, H. L. Enos, D. Gallagher, William F. Bottke, K. Getzandanner, Philip R. Christensen, C. W. V. Wolner, K. Fleshman, D. Poland, J. P. Emery, M.M. Riehl, D. Fennell, D. Sallitt, A. D. Rogers, M. Fitzgibbon, John H. Jones, S. Mullen, S. Salazar, S. Oliver, A. T. Polit, J. Cerna, A. Praet, Mark E. Holdridge, E. M. Ibrahim, Coralie D. Adam, J. de León, Christopher J. Miller, M. Ryle, J. Lyzhoft, M. Loveridge, C. Hoekenga, Brent J. Bos, S. Anwar, K. Chaffin, Devin L. Schrader, B. Lovelace, Romy D. Hanna, C. D. Adam, G. L. Mehall, K. L. Donaldson Hanna, F. Merlin, B. Wright, Guy Libourel, L. F. Lim, N. Shultz, Dante S. Lauretta, K. Hanley, Beth E. Clark, L. Le Corre, K. Thomas-Keprta, Moses Milazzo, W. Hagee, B. Page, M. Fisher, E. McDonough, D. Trang, S. Clemett, A. Rubi, A. Ingegneri, Scott A. Sandford, D. Dean, J. Freemantle, Michael D. Smith, Christopher W. Haberle, L. Nguyen, M. Fulchignoni, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL), Centre de Mise en Forme des Matériaux (CEMEF), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS]Physics [physics], 010504 meteorology & atmospheric sciences, Rubble, Stiffness, engineering.material, 010502 geochemistry & geophysics, 01 natural sciences, [SDU]Sciences of the Universe [physics], engineering, medicine, General Earth and Planetary Sciences, Geotechnical engineering, medicine.symptom, Pile, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

International audience

Published
2020
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23. Photometry of Particles Ejected From Active Asteroid (101955) Bennu

Author

A. B. Davis, E. J. Lessac-Chenen, J. M. Leonard, S. S. Balram-Knutson, C. K. Maleszewski, R. Garcia, Steven R. Chesley, Daniella DellaGiustina, K. N. Burke, A. S. French, J. Y. Pelgrift, Eric Christensen, Andrew J. Liounis, Maurizio Pajola, K. Alkiek, Ellen S. Howell, Kris J. Becker, R. Melikyan, Beth E. Clark, Bashar Rizk, Coralie D. Adam, C. Drouet d'Aubigny, Carl Hergenrother, J. N. Kidd, Marina Brozovic, F. Shelly, Robert A. Jacobson, Dante S. Lauretta, Brent J. Bos, Davide Farnocchia, Ryan S. Park, Theodore Kareta, Michael C. Nolan, Jian-Yang Li, and S. Selznick

Subjects
Photometry (astronomy), Geophysics, Space and Planetary Science, Geochemistry and Petrology, Asteroid, Earth and Planetary Sciences (miscellaneous), Astronomy, Geology
Published
2020
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24. Trajectory Estimation for Particles Observed in the Vicinity of (101955) Bennu

Author

C. W. V. Wolner, F. Shelly, J. Y. Pelgrift, Robert A. Jacobson, Jay W. McMahon, Daniel J. Scheeres, Eric Christensen, Carl Hergenrother, Coralie D. Adam, Steven R. Chesley, Marina Brozovic, Andrew J. Liounis, Davide Farnocchia, Michael C. Nolan, S. Selznick, Ben Rozitis, Brent J. Bos, A. S. French, Jamie Molaro, Y. Takahashi, E. J. Lessac-Chenen, Ryan S. Park, Dante S. Lauretta, A. B. Davis, Michael C. Moreau, David Vokrouhlický, Josh Emery, and J. M. Leonard

Subjects
Physics, 010504 meteorology & atmospheric sciences, Mass distribution, Spherical harmonics, 01 natural sciences, Ellipsoid, Computational physics, Geophysics, Gravitational field, Radiation pressure, Space and Planetary Science, Geochemistry and Petrology, Asteroid, Coefficient of restitution, Earth and Planetary Sciences (miscellaneous), SPHERES, 0105 earth and related environmental sciences
Abstract

We analyze the trajectories of 313 particles seen in the near‐Bennu environment between December 2018 and September 2019. Of these, 65% follow sub‐orbital trajectories, 20% undergo more than one orbital revolution around the asteroid, and 15% directly escape on hyperbolic trajectories. The median lifetime of these particles is ~6 h. The trajectories are sensitive to Bennu's gravitational field, which allows us to reliably estimate the spherical harmonic coefficients through degree 8 and to resolve nonuniform mass distribution through degree 3. The particles are perturbed by solar radiation pressure, enabling effective area‐to‐mass ratios to be estimated. By assuming that particles are oblate ellipsoids of revolution, and incorporating photometric measurements, we find a median axis ratio of 0.27 and diameters for equivalent‐volume spheres ranging from 0.22‐‐6.1 cm, with median 0.74 cm. Our size distribution agrees well with that predicted for fragmentation due to diurnal thermal cycling. Detailed models of known accelerations do not produce a match to the observed trajectories, so we also estimate empirical accelerations. These accelerations appear to be related to mismodeling of radiation pressure, but we cannot rule out contributions from mass loss. Most ejections take place at local solar times in the afternoon and evening (12:00‐‐24:00), although they occur at any time of day. We independently identify ten ejection events, some of which have previously been reported. We document a case where a particle ricocheted off the surface, revealing a coefficient of restitution 0.57±0.01 and demonstrating that some apparent ejections are not related to surface processes.

Published
2020
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25. Autonomous Detection of Particles and Tracks in Optical Images

Author

J. Y. Pelgrift, Derek S. Nelson, Carl Hergenrother, Michael C. Moreau, Jason M. Leonard, Jason C. Swenson, Steven R. Chesley, Andrew J. Liounis, Joshua R. Lyzhoft, J. Small, K. Getzandanner, Coralie D. Adam, Benjamin W. Ashman, Brent J. Bos, and Dante S. Lauretta

Subjects
010504 meteorology & atmospheric sciences, Computer science, lcsh:Astronomy, particle detection, FOS: Physical sciences, Image processing, Environmental Science (miscellaneous), 010502 geochemistry & geophysics, Tracking (particle physics), 01 natural sciences, particle tracking, lcsh:QB1-991, Sample return mission, active asteroid, Computer vision, Instrumentation and Methods for Astrophysics (astro-ph.IM), 0105 earth and related environmental sciences, Monocular, Spacecraft, business.industry, lcsh:QE1-996.5, image processing, Optical navigation, lcsh:Geology, Identification (information), Asteroid, General Earth and Planetary Sciences, Artificial intelligence, Astrophysics - Instrumentation and Methods for Astrophysics, business
Abstract

During its initial orbital phase in early 2019, the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) asteroid sample return mission detected small particles apparently emanating from the surface of the near-Earth asteroid (101955) Bennu in optical navigation images. Identification and characterization of the physical and dynamical properties of these objects became a mission priority in terms of both spacecraft safety and scientific investigation. Traditional techniques for particle identification and tracking typically rely on manual inspection and are often time-consuming. The large number of particles associated with the Bennu events and the mission criticality rendered manual inspection techniques infeasible for long-term operational support. In this work, we present techniques for autonomously detecting potential particles in monocular images and providing initial correspondences between observations in sequential images, as implemented for the OSIRIS-REx mission., Comment: 23 pages, 10 figures

Published
2020

26. In-Flight Calibration and Performance of the OSIRIS-REx Touch And Go Camera System (TAGCAMS)

Author

William M. Owen, K. Getzandanner, L. T. Seals, M. A. Ravine, J. Hikes, D. LeDuc, K. E. Gordon, K. Alkiek, J. N. Kidd, J. Y. Pelgrift, K. Drozd, J. Butt, Brent J. Bos, E. C. A. Church, Arlin E. Bartels, Conor O. Haney, R. Witherspoon, Coralie D. Adam, C. D. Norman, Rajendra Bhatt, Michael Caplinger, Eric M. Sahr, L. R. Chevres-Fernandez, David R. Doelling, Dante S. Lauretta, C. W. May, D. Huish, Andrew J. Liounis, Derek S. Nelson, Michael C. Moreau, Konstantin V. Khlopenkov, A. Wolfram, and R. Olds

Subjects
010504 meteorology & atmospheric sciences, Spacecraft, Pixel, Computer science, business.industry, Point source, Image quality, Stray light, Astronomy and Astrophysics, 01 natural sciences, Sample return mission, Space and Planetary Science, Asteroid, 0103 physical sciences, Calibration, business, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Remote sensing
Abstract

The Touch And Go Camera System (TAGCAMS) is a three-camera-head instrument onboard NASA’s OSIRIS-REx asteroid sample return mission spacecraft. The purpose of TAGCAMS is to facilitate navigation to the target asteroid, (101955) Bennu; confirm acquisition of the asteroid sample; document asteroid sample stowage; and provide supplementary imaging for OSIRIS-REx science investigations. During the almost two-year OSIRIS-REx outbound cruise phase we pursued nine TAGCAMS imaging campaigns to check, calibrate and characterize the camera system’s performance before asteroid arrival and proximity operations began in late 2018. The TAGCAMS in-flight calibration dataset provides the relevant information to enable the three cameras to complete their primary observation goals during asteroid operations. The key performance parameters that we investigated in flight included: linearity, responsivity (both point source and extended body), dark current, hot pixels, pointing, image geometry transformation, image quality and stray light. Analyses of the in-flight performance either confirmed the continued applicability of the TAGCAMS ground test results or substantially improved upon the ground test knowledge. In addition, the TAGCAMS calibration observations identified the source of a spacecraft outgassing feature that guided successful remediation efforts prior to asteroid arrival.

Published
2020
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27. Mass and Shape Determination of (101955) Bennu Using Differenced Data from Multiple OSIRIS-REx Mission Phases

Author

J. A. Seabrook, Erwan Mazarico, David D. Rowlands, J. Small, Jason M. Leonard, Dolan E. Highsmith, Sander Goossens, Joshua R. Lyzhoft, Andrew J. Liounis, Jason C. Swenson, Olivier S. Barnouin, Peter G. Antreasian, K. Getzandanner, J. Geeraert, Michael Daly, Coralie D. Adam, Benjamin W. Ashman, and Dante S. Lauretta

Subjects
Information retrieval, biology, business.industry, New Frontiers program, Data management plan, Astronomy and Astrophysics, biology.organism_classification, Planetary Data System, Geophysics, Software, Space and Planetary Science, Body mapping, Earth and Planetary Sciences (miscellaneous), Osiris, business, Geology
Abstract

This material is based on work supported by NASA under contract NNM10AA11C issued through the New Frontiers Program. S.G. acknowledges support from NASA under the CRESST II cooperative agreement with award No. 80GSFC17M0002. We are grateful to the entire OSIRIS-REx team for making the encounter with Bennu possible. Data are delivered to the Planetary Data System (PDS) according to the OSIRIS-REx Data Management Plan available in the OSIRISREx PDS archive. Raw through to calibrated data sets are available via the PDS at (https://sbn.psi.edu/pds/resource/ orex/), where there are directories for OLA (Daly et al. 2019), TAGCAMS (Bos et al. 2019), and Radio Science data. The OLA GDTM of Daly et al. (2020) can be found in the Small Body Mapping Tool available at https://sbmt.jhuapl.edu/ Object-Template.php?obj=77. Data images were generated with the freely available software GMT (Wessel et al. 2013). We thank two anonymous reviewers for their comments that improved the paper. We thank C. Wolner for editorial help.

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

Author

James H. Roberts, Benjamin Rozitis, Yun Zhang, E. B. Bierhaus, J. A. Seabrook, K. Getzandanner, Michael Daly, D. N. DellaGuistina, Clive Dickinson, P. Michel, Mark E. Perry, J. R. Weirich, Lydia C. Philpott, R. T. Daly, Robert Gaskell, Hannah C.M. Susorney, J. Geeraert, Andrew Ryan, Eric Palmer, G. Cunningham, Charles Brunet, M. Al Asad, Jason M. Leonard, M. C. Nolan, R. L. Ballouz, H. L. Enos, Olivier S. Barnouin, Dante S. Lauretta, D. Gaudreau, Coralie D. Adam, T. Haltigin, Bashar Rizk, Erwan Mazarico, Gregory A. Neumann, Catherine L. Johnson, Erica Jawin, Kevin J. Walsh, Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), Southwest Research Institute [Boulder] (SwRI), Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Lunar and Planetary Laboratory [Tucson] (LPL), and University of Arizona

Subjects
business.product_category, 010504 meteorology & atmospheric sciences, Longitudinal ridges, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], 01 natural sciences, 0103 physical sciences, Asymmetric distribution, Altimeter, Digital elevation model, 010303 astronomy & astrophysics, Geomorphology, Southern Hemisphere, Research Articles, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Multidisciplinary, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Northern Hemisphere, SciAdv r-articles, Wedge (mechanical device), Asteroid, [SDU]Sciences of the Universe [physics], business, Space Sciences, Geology, Research Article
Abstract

A lidar model of asteroid (101955) Bennu has a north-south asymmetry in shape and evidence of an early partial disruption., We investigate the shape of near-Earth asteroid (101955) Bennu by constructing a high-resolution (20 cm) global digital terrain model from laser altimeter data. By modeling the northern and southern hemispheres separately, we find that longitudinal ridges previously identified in the north extend into the south but are obscured there by surface material. In the south, more numerous large boulders effectively retain surface materials and imply a higher average strength at depth to support them. The north has fewer large boulders and more evidence of boulder dynamics (toppling and downslope movement) and surface flow. These factors result in Bennu’s southern hemisphere being rounder and smoother, whereas its northern hemisphere has higher slopes and a less regular shape. We infer an originally asymmetric distribution of large boulders followed by a partial disruption, leading to wedge formation in Bennu’s history.

Published
2020
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29. Episodes of particle ejection from the surface of the active asteroid (101955) Bennu

Author

Christine Hartzell, Guy Libourel, Bashar Rizk, Jian-Yang Li, Daniel J. Scheeres, David Vokrouhlický, C. Drouet d'Aubigny, Derek S. Nelson, Y. Takahashi, Robert A. Jacobson, Michael C. Moreau, Harold C. Connolly, Eric M. Sahr, William F. Bottke, J. A. Seabrook, J. Y. Pelgrift, Leilah K. McCarthy, J. M. Leonard, Ben Rozitis, Kris J. Becker, S. Selznick, J. de León, Josh Emery, Humberto Campins, Javier Licandro, Carl Hergenrother, Erica Jawin, Marina Brozovic, M. Al Asad, A. B. Davis, Florian Thuillet, Jamie Molaro, Pasquale Tricarico, E. J. Lessac-Chenen, Peter G. Antreasian, Jason P. Dworkin, C. K. Maleszewski, Davide Farnocchia, Carina Bennett, Jay W. McMahon, C. Manzoni, C. W. V. Wolner, Steven R. Chesley, P. Michel, Peter Jenniskens, Andrew J. Liounis, J. N. Kidd, Ronald-Louis Ballouz, Dathon Golish, Michael Daly, Daniella DellaGiustina, Daniel P. Glavin, H. L. Roper, William M. Owen, Coralie D. Adam, Brent J. Bos, B. May, Dante S. Lauretta, Laboratoire Kastler Brossel (LKB (Lhomond)), Université Pierre et Marie Curie - Paris 6 (UPMC)-Fédération de recherche du Département de physique de l'Ecole Normale Supérieure - ENS Paris (FRDPENS), Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Dept. of Physics, University of Central Florida [Orlando] (UCF), IHU-LIRYC, Université Bordeaux Segalen - Bordeaux 2-CHU Bordeaux [Bordeaux], Universidad Autonoma de Nuevo Leon [Mexique] (UANL), NASA Goddard Space Flight Center (GSFC), Laboratoire de physique de l'état condensé (LPEC), Centre National de la Recherche Scientifique (CNRS)-Le Mans Université (UM), Dipartimento di Matematica, University of Pisa - Università di Pisa, Université de Washington Seattle, University of Michigan Medical School [Ann Arbor], University of Michigan [Ann Arbor], University of Michigan System-University of Michigan System, Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Instituto de Astrofisica de Canarias (IAC), Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, The Open University [Milton Keynes] (OU), Institute of Astronomy, Charles University [Prague] (CU), ANR-15-IDEX-0001,UCA JEDI,Idex UCA JEDI(2015), Fédération de recherche du Département de physique de l'Ecole Normale Supérieure - ENS Paris (FRDPENS), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), University of Central Florida [Orlando], CHU Bordeaux [Bordeaux]-Université Bordeaux Segalen - Bordeaux 2, Le Mans Université (UM)-Centre National de la Recherche Scientifique (CNRS), Centre de Recherches Pétrographiques et Géochimiques (CRPG), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Politecnico di Milano [Milan] (POLIMI), Service d'hépato-gastro-entérologie [Hôpital Saint-Louis], Groupe Hospitalier Saint Louis - Lariboisière - Fernand Widal [Paris], Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP), Laboratoire Avancé de Spectroscopie pour les Intéractions la Réactivité et l'Environnement - UMR 8516 (LASIRe), Ecole Nationale Supérieure de Chimie de Lille (ENSCL)-Université de Lille-Centre National de la Recherche Scientifique (CNRS), Charles University [Prague], and ANR: 15-IDEX-0001,UCA JEDI,Idex UCA JEDI(2015)

Subjects
Solar System, 010504 meteorology & atmospheric sciences, Origin of water on Earth, Population, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Astrophysics, 01 natural sciences, 0103 physical sciences, education, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, education.field_of_study, Multidisciplinary, Meteoroid, Spacecraft, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], business.industry, 13. Climate action, Asteroid, [SDU]Sciences of the Universe [physics], Solar time, Physics::Space Physics, Astrophysics::Earth and Planetary Astrophysics, business, Orbit determination, Geology
Abstract

INTRODUCTION Active asteroids are small bodies in the Solar System that show ongoing mass loss, such as the ejection of dust, which may be caused by large impacts, volatile release, or rotational acceleration. Studying them informs our understanding of the evolution and destruction of asteroids and the origin of volatile materials such as water on Earth. The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) spacecraft has rendezvoused with the near-Earth asteroid (101955) Bennu. The selection of Bennu as the OSIRIS-REx target was partially based on its spectral similarity to some active asteroids. Observations designed to detect mass loss at Bennu were conducted from Earth and during the spacecraft’s approach, but no signs of asteroid activity were found. However, when the spacecraft entered orbit in January 2019, we serendipitously observed particles in the vicinity of Bennu that had apparently been ejected from its surface. RATIONALE We analyzed the properties and behavior of particles ejected from Bennu to determine the possible mechanisms of ejection and provide understanding of the broader population of active asteroids. Images obtained by the spacecraft indicate multiple discrete ejection events with a range of energies and resultant particle trajectories. We characterized three large ejection events that respectively occurred on 6 January, 19 January, and 11 February 2019. Tracking of individual particles across multiple images by means of optical navigation techniques provided the initial conditions for orbit determination modeling. By combining these approaches, we estimated the locations and times of ejection events and determined initial velocity vectors of particles. We estimated the particle sizes and the minimum energies of the ejection events using a particle albedo and density consistent with observations of Bennu. RESULTS Particles with diameters from 3 m s–1. Estimated energies ranged from 270 mJ for the 6 January event to 8 mJ for the 11 February event. The three events arose from widely separated sites, which do not show any obvious geological distinction from the rest of Bennu’s surface. However, these events all occurred in the late afternoon, between about 15:00 and 18:00 local solar time. In addition to discrete ejection events, we detected a persistent background of particles in the Bennu environment. Some of these background particles have been observed to persist on temporary orbits that last several days—in one case, with a semimajor axis >1 km. The orbital characteristics of these gravitationally bound objects make it possible to determine the ratio of their cross-sectional area to their mass. Combined with their photometric phase functions, this information constrains the parameter space of the particles’ diameters, densities, and albedos. CONCLUSION Plausible mechanisms for the large ejection events include thermal fracturing, volatile release through dehydration of phyllosilicates, and meteoroid impacts. The late-afternoon timing of the events is consistent with any of these mechanisms. Bennu’s boulder geology indicates that thermal fracturing, perhaps enhanced by volatile release, could occur on the asteroid surface. Smaller events, especially those that occur on the night side of Bennu, could be attributable to reimpacting particles. Our observations classify Bennu as an active asteroid. Active asteroids are commonly identified by major mass loss events observable with telescopes, on scales much greater than we observed at Bennu. Our findings indicate that there is a continuum of mass loss event magnitudes among active asteroids.

Published
2019
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