1
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Robin CQ, Duchene A, Murdoch N, Vincent JB, Lucchetti A, Pajola M, Ernst CM, Daly RT, Barnouin OS, Raducan SD, Michel P, Hirabayashi M, Stott A, Cuervo G, Jawin ER, Trigo-Rodriguez JM, Parro LM, Sunday C, Vivet D, Mimoun D, Rivkin AS, Chabot NL. Mechanical properties of rubble pile asteroids (Dimorphos, Itokawa, Ryugu, and Bennu) through surface boulder morphological analysis. Nat Commun 2024; 15:6203. [PMID: 39079972 PMCID: PMC11289397 DOI: 10.1038/s41467-024-50147-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Accepted: 05/17/2024] [Indexed: 08/02/2024] Open
Abstract
Planetary defense efforts rely on estimates of the mechanical properties of asteroids, which are difficult to constrain accurately from Earth. The mechanical properties of asteroid material are also important in the interpretation of the Double Asteroid Redirection Test (DART) impact. Here we perform a detailed morphological analysis of the surface boulders on Dimorphos using images, the primary data set available from the DART mission. We estimate the bulk angle of internal friction of the boulders to be 32.7 ± 2. 5° from our measurements of the roundness of the 34 best-resolved boulders ranging in size from 1.67-6.64 m. The elongated nature of the boulders around the DART impact site implies that they were likely formed through impact processing. Finally, we find striking similarities in the morphology of the boulders on Dimorphos with those on other rubble pile asteroids (Itokawa, Ryugu and Bennu). This leads to very similar internal friction angles across the four bodies and suggests that a common formation mechanism has shaped the boulders. Our results provide key inputs for understanding the DART impact and for improving our knowledge about the physical properties, the formation and the evolution of both near-Earth rubble-pile and binary asteroids.
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Affiliation(s)
- Colas Q Robin
- Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France.
| | - Alexia Duchene
- Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - Naomi Murdoch
- Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | | | | | | | - Carolyn M Ernst
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
| | - R Terik Daly
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
| | | | | | - Patrick Michel
- Côte d'Azur University, Côte d'Azur Observatory, CNRS, Lagrange Laboratory, Nice, France
- The University of Tokyo, Department of Systems Innovation, School of Engineering, Tokyo, Japan
| | | | - Alexander Stott
- Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - Gabriela Cuervo
- Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - Erica R Jawin
- Smithonian National Air and Space Museum, Washington, DC, USA
| | - Josep M Trigo-Rodriguez
- Institute of Space Sciences (CSIC-IEEC), Campus UAB, Carrer Can Magrans s/n, Cerdanyola del Valles, Barcelona, Catalonia, Spain
| | - Laura M Parro
- IUFACyT, Alicante University, San Vicente del Raspeig, 03080, Alicante, Spain
| | - Cecily Sunday
- Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
- University of Maryland, College Park, MD, USA
| | - Damien Vivet
- Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - David Mimoun
- Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - Andrew S Rivkin
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
| | - Nancy L Chabot
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
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2
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Lucchetti A, Cambioni S, Nakano R, Barnouin OS, Pajola M, Penasa L, Tusberti F, Ramesh KT, Dotto E, Ernst CM, Daly RT, Mazzotta Epifani E, Hirabayashi M, Parro L, Poggiali G, Campo Bagatin A, Ballouz RL, Chabot NL, Michel P, Murdoch N, Vincent JB, Karatekin Ö, Rivkin AS, Sunshine JM, Kohout T, Deshapriya JDP, Hasselmann PHA, Ieva S, Beccarelli J, Ivanovski SL, Rossi A, Ferrari F, Rossi C, Raducan SD, Steckloff J, Schwartz S, Brucato JR, Dall'Ora M, Zinzi A, Cheng AF, Amoroso M, Bertini I, Capannolo A, Caporali S, Ceresoli M, Cremonese G, Della Corte V, Gai I, Gomez Casajus L, Gramigna E, Impresario G, Lasagni Manghi R, Lavagna M, Lombardo M, Modenini D, Palumbo P, Perna D, Pirrotta S, Tortora P, Zannoni M, Zanotti G. Fast boulder fracturing by thermal fatigue detected on stony asteroids. Nat Commun 2024; 15:6206. [PMID: 39080275 PMCID: PMC11289370 DOI: 10.1038/s41467-024-50145-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Accepted: 05/09/2024] [Indexed: 08/02/2024] Open
Abstract
Spacecraft observations revealed that rocks on carbonaceous asteroids, which constitute the most numerous class by composition, can develop millimeter-to-meter-scale fractures due to thermal stresses. However, signatures of this process on the second-most populous group of asteroids, the S-complex, have been poorly constrained. Here, we report observations of boulders' fractures on Dimorphos, which is the moonlet of the S-complex asteroid (65803) Didymos, the target of NASA's Double Asteroid Redirection Test (DART) planetary defense mission. We show that the size-frequency distribution and orientation of the mapped fractures are consistent with formation through thermal fatigue. The fractures' preferential orientation supports that these have originated in situ on Dimorphos boulders and not on Didymos boulders later transferred to Dimorphos. Based on our model of the fracture propagation, we propose that thermal fatigue on rocks exposed on the surface of S-type asteroids can form shallow, horizontally propagating fractures in much shorter timescales (100 kyr) than in the direction normal to the boulder surface (order of Myrs). The presence of boulder fields affected by thermal fracturing on near-Earth asteroid surfaces may contribute to an enhancement in the ejected mass and momentum from kinetic impactors when deflecting asteroids.
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Affiliation(s)
- A Lucchetti
- INAF-Astronomical Observatory of Padova, Vic. Osservatorio 5, 35122, Padova, Italy.
| | - S Cambioni
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - R Nakano
- Daniel Guggenheim School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA
- Department of Aerospace Engineering, Auburn University, Auburn, AL, 36849, USA
| | - O S Barnouin
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
| | - M Pajola
- INAF-Astronomical Observatory of Padova, Vic. Osservatorio 5, 35122, Padova, Italy
| | - L Penasa
- INAF-Astronomical Observatory of Padova, Vic. Osservatorio 5, 35122, Padova, Italy
| | - F Tusberti
- INAF-Astronomical Observatory of Padova, Vic. Osservatorio 5, 35122, Padova, Italy
| | - K T Ramesh
- Johns Hopkins University, Baltimore, MD, USA
| | - E Dotto
- INAF-Osservatorio Astronomico di Roma, Monte Porzio Catone, Roma, Italy
| | - C M Ernst
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
| | - R T Daly
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
| | | | - M Hirabayashi
- Daniel Guggenheim School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA
- Department of Aerospace Engineering, Auburn University, Auburn, AL, 36849, USA
| | - L Parro
- IUFACyT. Universidad de Alicante, Alicante, Spain
- University of Arizona, Tucson, AZ, USA
- Universidad Complutense, Madrid, Spain
| | - G Poggiali
- INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy
- LESIA-Observatorie de Paris PSL, Paris, France
| | - A Campo Bagatin
- IUFACyT. Universidad de Alicante, Alicante, Spain
- Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Alicante, Spain
| | - R-L Ballouz
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
| | - N L Chabot
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
| | - P Michel
- Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France
- School of Engineering, Department of Systems Innovation, The University of Tokyo, Tokyo, Japan
| | - N Murdoch
- Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - J B Vincent
- DLR Institute of Planetary Research, Berlin, Germany
| | - Ö Karatekin
- Royal Observatory of Belgium, Uccle, Belgium
| | - A S Rivkin
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
| | - J M Sunshine
- Departments of Astronomy and Geology, University of Maryland, College Park, MD, USA
| | - T Kohout
- University of Helsinki, Helsinki, Finland
- Institute of Geology of the Czech Academy of Sciences, Prague, Czech Republic
| | - J D P Deshapriya
- INAF-Osservatorio Astronomico di Roma, Monte Porzio Catone, Roma, Italy
| | - P H A Hasselmann
- INAF-Osservatorio Astronomico di Roma, Monte Porzio Catone, Roma, Italy
| | - S Ieva
- INAF-Osservatorio Astronomico di Roma, Monte Porzio Catone, Roma, Italy
| | - J Beccarelli
- INAF-Astronomical Observatory of Padova, Vic. Osservatorio 5, 35122, Padova, Italy
| | - S L Ivanovski
- INAF-Osservatorio Astronomico di Trieste, Trieste, Italy
| | - A Rossi
- IFAC-CNR, Sesto Fiorentino, Firenze, Italy
| | - F Ferrari
- Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano - Bovisa Campus, Milano, Italy
| | - C Rossi
- INAF-Astronomical Observatory of Padova, Vic. Osservatorio 5, 35122, Padova, Italy
| | - S D Raducan
- Space Research and Planetary Sciences, Physikalisches Institut, University of Bern, Bern, Switzerland
| | - J Steckloff
- Planetary Science Institute, Tucson, AZ, USA
| | - S Schwartz
- Planetary Science Institute, Tucson, AZ, USA
| | - J R Brucato
- INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy
| | - M Dall'Ora
- INAF-Osservatorio Astronomico di Capodimonte, Napoli, Italy
| | - A Zinzi
- Space Science Data Center - ASI, Roma, Italy
| | - A F Cheng
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
| | - M Amoroso
- Agenzia Spaziale Italiana, Roma, Italy
| | - I Bertini
- Dipartimento di Scienze & Tecnologie, Università degli Studi di Napoli "Parthenope", Centro Direzionale, Napoli, Italy
| | - A Capannolo
- Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Université de Toulouse, Toulouse, France
| | - S Caporali
- INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy
| | - M Ceresoli
- Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano - Bovisa Campus, Milano, Italy
| | - G Cremonese
- INAF-Astronomical Observatory of Padova, Vic. Osservatorio 5, 35122, Padova, Italy
| | - V Della Corte
- INAF-Osservatorio Astronomico di Capodimonte, Napoli, Italy
| | - I Gai
- Dipartimento di Ingegneria Industriale, Alma Mater Studiorum - Università di Bologna, Forlì, Italy
| | - L Gomez Casajus
- Centro Interdipartimentale di Ricerca Industriale Aerospaziale, Alma Mater Studiorum, Università di Bologna, Forlì, Italy
| | - E Gramigna
- Dipartimento di Ingegneria Industriale, Alma Mater Studiorum - Università di Bologna, Forlì, Italy
| | | | - R Lasagni Manghi
- Dipartimento di Ingegneria Industriale, Alma Mater Studiorum - Università di Bologna, Forlì, Italy
| | - M Lavagna
- Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano - Bovisa Campus, Milano, Italy
| | - M Lombardo
- Dipartimento di Ingegneria Industriale, Alma Mater Studiorum - Università di Bologna, Forlì, Italy
| | - D Modenini
- Dipartimento di Ingegneria Industriale, Alma Mater Studiorum - Università di Bologna, Forlì, Italy
- Centro Interdipartimentale di Ricerca Industriale Aerospaziale, Alma Mater Studiorum, Università di Bologna, Forlì, Italy
| | - P Palumbo
- INAF-Istituto di Astrofisica e Planetologia Spaziali, Roma, Italy
| | - D Perna
- INAF-Osservatorio Astronomico di Roma, Monte Porzio Catone, Roma, Italy
| | | | - P Tortora
- Dipartimento di Ingegneria Industriale, Alma Mater Studiorum - Università di Bologna, Forlì, Italy
- Centro Interdipartimentale di Ricerca Industriale Aerospaziale, Alma Mater Studiorum, Università di Bologna, Forlì, Italy
| | - M Zannoni
- Dipartimento di Ingegneria Industriale, Alma Mater Studiorum - Università di Bologna, Forlì, Italy
- Centro Interdipartimentale di Ricerca Industriale Aerospaziale, Alma Mater Studiorum, Università di Bologna, Forlì, Italy
| | - G Zanotti
- Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano - Bovisa Campus, Milano, Italy
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3
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Walsh KJ, Ballouz RL, Jawin ER, Avdellidou C, Barnouin OS, Bennett CA, Bierhaus EB, Bos BJ, Cambioni S, Connolly HC, Delbo M, DellaGiustina DN, DeMartini J, Emery JP, Golish DR, Haas PC, Hergenrother CW, Ma H, Michel P, Nolan MC, Olds R, Rozitis B, Richardson DC, Rizk B, Ryan AJ, Sánchez P, Scheeres DJ, Schwartz SR, Selznick SH, Zhang Y, Lauretta DS. Near-zero cohesion and loose packing of Bennu's near subsurface revealed by spacecraft contact. SCIENCE ADVANCES 2022; 8:eabm6229. [PMID: 35857450 PMCID: PMC9262326 DOI: 10.1126/sciadv.abm6229] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
When the OSIRIS-REx spacecraft pressed its sample collection mechanism into the surface of Bennu, it provided a direct test of the poorly understood near-subsurface physical properties of rubble-pile asteroids, which consist of rock fragments at rest in microgravity. Here, we find that the forces measured by the spacecraft are best modeled as a granular bed with near-zero cohesion that is half as dense as the bulk asteroid. The low gravity of a small rubble-pile asteroid such as Bennu effectively weakens its near subsurface by not compressing the upper layers, thereby minimizing the influence of interparticle cohesion on surface geology. The underdensity and weak near subsurface should be global properties of Bennu and not localized to the contact point.
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Affiliation(s)
- Kevin J. Walsh
- Southwest Research Institute, Boulder, CO, USA
- Corresponding author.
| | - Ronald-Louis Ballouz
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
| | - Erica R. Jawin
- National Air and Space Museum, Smithsonian Institution, Washington, DC, USA
| | - Chrysa Avdellidou
- Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
| | | | - Carina A. Bennett
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | - Brent J. Bos
- NASA Goddard Space Flight Center, Greenbelt, MD, USA
| | - Saverio Cambioni
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Harold C. Connolly
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
- Department of Geology, Rowan University, Glassboro, NJ, USA
| | - Marco Delbo
- Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
| | | | - Joseph DeMartini
- Department of Astronomy, University of Maryland, College Park, MD, USA
| | - Joshua P. Emery
- Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ, USA
| | - Dathon R. Golish
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | | | - Huikang Ma
- Lockheed Martin Space, Littleton, CO, USA
| | - Patrick Michel
- Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
| | - Michael C. Nolan
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - Ryan Olds
- Lockheed Martin Space, Littleton, CO, USA
| | - Benjamin Rozitis
- School of Physical Sciences, The Open University, Milton Keynes, UK
| | | | - Bashar Rizk
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - Andrew J. Ryan
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - Paul Sánchez
- Colorado Center for Astrodynamics Research, University of Colorado Boulder, Boulder, CO, USA
| | - Daniel J. Scheeres
- Colorado Center for Astrodynamics Research, University of Colorado Boulder, Boulder, CO, USA
- Smead Aerospace Engineering Sciences Department, University of Colorado Boulder, Boulder, CO, USA
| | - Stephen R. Schwartz
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
- Planetary Science Institute, Tucson, AZ, USA
| | | | - Yun Zhang
- Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
| | - Dante S. Lauretta
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
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4
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Golish DR, Simon AA, Reuter DC, Ferrone S, Clark BE, Li JY, DellaGiustina DN, Drouet d’Aubigny C, Rizk B, Lauretta DS. Cross-Instrument Comparison of MapCam and OVIRS on OSIRIS-REx. SPACE SCIENCE REVIEWS 2022; 218:5. [PMID: 35250103 PMCID: PMC8885487 DOI: 10.1007/s11214-022-00873-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Accepted: 02/08/2022] [Indexed: 06/14/2023]
Abstract
Two of the instruments onboard the OSIRIS-REx spacecraft, the MapCam color imager and the OVIRS visible and infrared spectrometer, observed the surface of asteroid (101955) Bennu in partially overlapping wavelengths. Significant scientific advances have been enabled by using data from these two instruments in tandem, but a robust statistical understanding of their relationship is needed for future analyses to cross-compare their data as accurately and sensitively as possible. Here we present a cross-instrument comparison of data acquired by MapCam and OVIRS, including methods and results for all global and site-specific observation campaigns in which both instruments were active. In our analysis, we consider both the absolute radiometric offset and the relative (normalized) variation between the two instruments; we find that both depend strongly on the photometric and instrumental conditions during the observation. The two instruments have a large absolute offset (>15%) due to their independent radiometric calibrations. However, they are very consistent (relative offset as low as 1%) when each instrument's response is normalized at a single wavelength, particularly at low phase angles where shadows on Bennu's rough surface are minimized. We recommend using the global datasets acquired at 12:30 pm local solar time for cross-comparisons; data acquired at higher phase angles have larger uncertainties.
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Affiliation(s)
- D. R. Golish
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ USA
| | - A. A. Simon
- NASA Goddard Space Flight Center, Greenbelt, MD USA
| | - D. C. Reuter
- NASA Goddard Space Flight Center, Greenbelt, MD USA
| | - S. Ferrone
- Department of Physics and Astronomy, Ithaca College, Ithaca, NY USA
| | - B. E. Clark
- Department of Physics and Astronomy, Ithaca College, Ithaca, NY USA
| | - J.-Y. Li
- Planetary Science Institute, Tucson, AZ USA
| | | | | | - B. Rizk
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ USA
| | - D. S. Lauretta
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ USA
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5
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Velbel MA, Zolensky ME. Thermal metamorphism of CM chondrites: A dehydroxylation-based peak-temperature thermometer and implications for sample return from asteroids Ryugu and Bennu. METEORITICS & PLANETARY SCIENCE 2021; 56:546-585. [PMID: 34262245 PMCID: PMC8252763 DOI: 10.1111/maps.13636] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Accepted: 01/17/2021] [Indexed: 06/13/2023]
Abstract
The target bodies of C-complex asteroid sample return missions are carbonaceous chondrite-like near-Earth asteroids (NEAs), chosen for the abundance and scientific importance of their organic compounds and "hydrous" (including hydroxylated) minerals, such as serpentine-group phyllosilicates. Science objectives include returning samples of pristine carbonaceous regolith from asteroids for study of the nature, history, and distribution of its constituent minerals, organic material, and other volatiles. Heating after the natural aqueous alteration that formed the abundant phyllosilicates in CM and similar carbonaceous chondrites dehydroxylated them and altered or decomposed other volumetrically minor constituents (e.g., carbonates, sulfides, organic molecules; Tonui et al. 2003, 2014). We propose a peak-temperature thermometer based on dehydroxylation as measured by analytical totals from electron probe microanalysis (EPMA) of matrices in a number of heated and aqueously altered (but not further heated) CM chondrites. Some CM lithologies in Maribo and Sutter's Mill do not exhibit the matrix dehydroxylation expected for surface temperatures expected from insolation of meteoroids with their known orbital perihelia. This suggests that insolated-heated meteoroid surfaces were lost by ablation during passage through Earth's atmosphere, and that insolation-heated material is more likely to be encountered among returned asteroid regolith samples than in meteorites. More generally, several published lines of evidence suggest that episodic heating of some CM material, most likely by impacts, continued intermittently and locally up to billions of years after assembly and early heating of ancestral CM chondrite bodies. Mission spectroscopic measures of hydration can be used to estimate the extent of dehydroxylation, and the new dehydroxylation thermometer can be used directly to select fragments of returned samples most likely to contain less thermally altered inventories of primitive organic molecules.
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Affiliation(s)
- Michael A. Velbel
- Department of Earth and Environmental SciencesMichigan State University288 Farm Lane, Room 207, Natural Sciences BuildingEast LansingMichigan48824–1115USA
- Division of MeteoritesDepartment of Mineral SciencesNational Museum of Natural HistorySmithsonian InstitutionWashingtonDistrict of Columbia20013–7012USA
| | - Michael E. Zolensky
- X12 Astromaterials Research and Exploration ScienceNASA Johnson Space CenterHoustonTexas77058USA
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6
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Bennu's near-Earth lifetime of 1.75 million years inferred from craters on its boulders. Nature 2020; 587:205-209. [PMID: 33106686 DOI: 10.1038/s41586-020-2846-z] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Accepted: 09/15/2020] [Indexed: 11/08/2022]
Abstract
An asteroid's history is determined in large part by its strength against collisions with other objects1,2 (impact strength). Laboratory experiments on centimetre-scale meteorites3 have been extrapolated and buttressed with numerical simulations to derive the impact strength at the asteroid scale4,5. In situ evidence of impacts on boulders on airless planetary bodies has come from Apollo lunar samples6 and images of the asteroid (25143) Itokawa7. 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 ± 0.75 million years.
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7
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Simon AA, Kaplan HH, Hamilton VE, Lauretta DS, Campins H, Emery JP, Barucci MA, DellaGiustina DN, Reuter DC, Sandford SA, Golish DR, Lim LF, Ryan A, Rozitis B, Bennett CA. Widespread carbon-bearing materials on near-Earth asteroid (101955) Bennu. Science 2020; 370:science.abc3522. [PMID: 33033153 DOI: 10.1126/science.abc3522] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 08/27/2020] [Indexed: 11/02/2022]
Abstract
Asteroid (101955) Bennu is a dark asteroid on an Earth-crossing orbit that is thought to have assembled from the fragments of an ancient collision. We use spatially resolved visible and near-infrared spectra of Bennu to investigate its surface properties and composition. In addition to a hydrated phyllosilicate band, we detect a ubiquitous 3.4-micrometer absorption feature, which we attribute to a mix of organic and carbonate materials. The shape and depth of this absorption feature vary across Bennu's surface, spanning the range seen among similar main-belt asteroids. The distribution of the absorption feature does not correlate with temperature, reflectance, spectral slope, or hydrated minerals, although some of those characteristics correlate with each other. The deepest 3.4-micrometer absorptions occur on individual boulders. The variations may be due to differences in abundance, recent exposure, or space weathering.
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Affiliation(s)
- Amy A Simon
- Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA.
| | | | | | - Dante S Lauretta
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - Humberto Campins
- Department of Physics, University of Central Florida, Orlando, FL, USA
| | - Joshua P Emery
- Department of Astronomy and Planetary Sciences, Northern Arizona University, Flagstaff, AZ, USA
| | - M Antonietta Barucci
- Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique, Observatoire de Paris, Université Paris Sciences et Lettres, Centre National de la Recherche Scientifique, Université de Paris, Sorbonne Université, Meudon, France
| | | | - Dennis C Reuter
- Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
| | | | - Dathon R Golish
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - Lucy F Lim
- Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
| | - Andrew Ryan
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - Benjamin Rozitis
- School of Physical Sciences, The Open University, Milton Keynes, UK
| | - Carina A Bennett
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
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8
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DellaGiustina DN, Burke KN, Walsh KJ, Smith PH, Golish DR, Bierhaus EB, Ballouz RL, Becker TL, Campins H, Tatsumi E, Yumoto K, Sugita S, Deshapriya JDP, Cloutis EA, Clark BE, Hendrix AR, Sen A, Al Asad MM, Daly MG, Applin DM, Avdellidou C, Barucci MA, Becker KJ, Bennett CA, Bottke WF, Brodbeck JI, Connolly HC, Delbo M, de Leon J, Drouet d'Aubigny CY, Edmundson KL, Fornasier S, Hamilton VE, Hasselmann PH, Hergenrother CW, Howell ES, Jawin ER, Kaplan HH, Le Corre L, Lim LF, Li JY, Michel P, Molaro JL, Nolan MC, Nolau J, Pajola M, Parkinson A, Popescu M, Porter NA, Rizk B, Rizos JL, Ryan AJ, Rozitis B, Shultz NK, Simon AA, Trang D, Van Auken RB, Wolner CWV, Lauretta DS. Variations in color and reflectance on the surface of asteroid (101955) Bennu. Science 2020; 370:science.abc3660. [PMID: 33033157 DOI: 10.1126/science.abc3660] [Citation(s) in RCA: 58] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Accepted: 09/24/2020] [Indexed: 11/02/2022]
Abstract
Visible-wavelength color and reflectance provide information about the geologic history of planetary surfaces. Here we present multispectral images (0.44 to 0.89 micrometers) 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 region (i.e., become bluer at shorter wavelengths), then brighten in the visible to near-infrared region, leading to Bennu's moderately blue average color. Craters indicate that the time scale of these color changes is ~105 years. We attribute the reflectance and color variation to a combination of primordial heterogeneity and varying exposure ages.
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Affiliation(s)
- D N DellaGiustina
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA. .,Department of Geosciences, University of Arizona, Tucson, AZ, USA
| | - K N Burke
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - K J Walsh
- Southwest Research Institute, Boulder, CO, USA
| | - P H Smith
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - D R Golish
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | - R-L Ballouz
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - T L Becker
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - H Campins
- Department of Physics, University of Central Florida, Orlando, FL, USA
| | - E Tatsumi
- Instituto de Astrofísica de Canarias and Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain.,Department of Earth and Planetary Science, University of Tokyo, Tokyo, 113-0033, Japan
| | - K Yumoto
- Department of Earth and Planetary Science, University of Tokyo, Tokyo, 113-0033, Japan
| | - S Sugita
- Department of Earth and Planetary Science, University of Tokyo, Tokyo, 113-0033, Japan
| | - J D Prasanna Deshapriya
- LESIA (Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique), Observatoire de Paris, Université PSL (Paris Sciences & Lettres), CNRS (Centre National de la Recherche Scientifique), Université de Paris, Sorbonne Université, 92195 Meudon, France
| | - E A Cloutis
- Department of Geography, University of Winnipeg, Winnipeg, MB R3B 2E9, Canada
| | - B E Clark
- Department of Physics and Astronomy, Ithaca College, Ithaca, NY, USA
| | - A R Hendrix
- Planetary Science Institute, Tucson, AZ, USA
| | - A Sen
- Department of Physics and Astronomy, Ithaca College, Ithaca, NY, USA
| | - M M Al Asad
- Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada
| | - M G Daly
- The Centre for Research in Earth and Space Science, York University, Toronto, ON, Canada
| | - D M Applin
- Department of Geography, University of Winnipeg, Winnipeg, MB R3B 2E9, Canada
| | - C Avdellidou
- Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France
| | - M A Barucci
- LESIA (Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique), Observatoire de Paris, Université PSL (Paris Sciences & Lettres), CNRS (Centre National de la Recherche Scientifique), Université de Paris, Sorbonne Université, 92195 Meudon, France
| | - K J Becker
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - C A Bennett
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - W F Bottke
- Southwest Research Institute, Boulder, CO, USA
| | - J I Brodbeck
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - H C Connolly
- Department of Geology, Rowan University, Glassboro, NJ, USA
| | - M Delbo
- Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France
| | - J de Leon
- Instituto de Astrofísica de Canarias and Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain
| | | | - K L Edmundson
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - S Fornasier
- LESIA (Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique), Observatoire de Paris, Université PSL (Paris Sciences & Lettres), CNRS (Centre National de la Recherche Scientifique), Université de Paris, Sorbonne Université, 92195 Meudon, France.,Institut Universitaire de France (IUF), 1 rue Descartes, 75231 Paris CEDEX 05, France
| | | | - P H Hasselmann
- LESIA (Laboratoire d'Etudes Spatiales et d'Instrumentation en Astrophysique), Observatoire de Paris, Université PSL (Paris Sciences & Lettres), CNRS (Centre National de la Recherche Scientifique), Université de Paris, Sorbonne Université, 92195 Meudon, France
| | - C W Hergenrother
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - E S Howell
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - E R Jawin
- Smithsonian Institution National Museum of Natural History, Washington, DC, USA
| | - H H Kaplan
- NASA Goddard Space Flight Center, Greenbelt, MD, USA
| | - L Le Corre
- Planetary Science Institute, Tucson, AZ, USA
| | - L F Lim
- Smithsonian Institution National Museum of Natural History, Washington, DC, USA
| | - J Y Li
- Planetary Science Institute, Tucson, AZ, USA
| | - P Michel
- Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France
| | - J L Molaro
- Planetary Science Institute, Tucson, AZ, USA
| | - M C Nolan
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - J Nolau
- Lockheed Martin Space, Littleton, CO, USA
| | - M Pajola
- Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Padova, Padua, Italy
| | - A Parkinson
- Department of Geography, University of Winnipeg, Winnipeg, MB R3B 2E9, Canada
| | - M Popescu
- Astronomical Institute of the Romanian Academy, Bucharest, Romania.,Instituto de Astrofísica de Canarias and Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain
| | - N A Porter
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - B Rizk
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - J L Rizos
- Instituto de Astrofísica de Canarias and Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain
| | - A J Ryan
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - B Rozitis
- The School of Physical Sciences, The Open University, Milton Keynes, UK
| | - N K Shultz
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - A A Simon
- NASA Goddard Space Flight Center, Greenbelt, MD, USA
| | - D Trang
- University of Hawai'i at Mānoa, Hawai'i Institute of Geophysics and Planetology, Honolulu, HI, USA
| | - R B Van Auken
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - C W V Wolner
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - D S Lauretta
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
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9
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Rozitis B, Ryan AJ, Emery JP, Christensen PR, Hamilton VE, Simon AA, Reuter DC, Al Asad M, Ballouz RL, Bandfield JL, Barnouin OS, Bennett CA, Bernacki M, Burke KN, Cambioni S, Clark BE, Daly MG, Delbo M, DellaGiustina DN, Elder CM, Hanna RD, Haberle CW, Howell ES, Golish DR, Jawin ER, Kaplan HH, Lim LF, Molaro JL, Munoz DP, Nolan MC, Rizk B, Siegler MA, Susorney HCM, Walsh KJ, Lauretta DS. Asteroid (101955) Bennu's weak boulders and thermally anomalous equator. SCIENCE ADVANCES 2020; 6:eabc3699. [PMID: 33033037 PMCID: PMC7544501 DOI: 10.1126/sciadv.abc3699] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Accepted: 09/09/2020] [Indexed: 05/18/2023]
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.
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Affiliation(s)
- B Rozitis
- School of Physical Sciences, The Open University, Milton Keynes, UK.
| | - A J Ryan
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - J P Emery
- Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ, USA
| | - P R Christensen
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
| | | | - A A Simon
- NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD, USA
| | - D C Reuter
- NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD, USA
| | - M Al Asad
- Department of Earth, Atmospheric, and Ocean Science, University of British Columbia, Vancouver, BC, Canada
| | - R-L Ballouz
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | | | - O S Barnouin
- The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
| | - C A Bennett
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - M Bernacki
- Mines ParisTech, PSL Research University, CEMEF-Centre de mise en forme des matériaux, Sophia Antipolis Cedex, France
| | - K N Burke
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - S Cambioni
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - B E Clark
- Department of Physics and Astronomy, Ithaca College, Ithaca, NY, USA
| | - M G Daly
- The Centre for Research in Earth and Space Science, York University, Toronto, ON, Canada
| | - M Delbo
- Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France
| | - D N DellaGiustina
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - C M Elder
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
| | - R D Hanna
- Jackson School of Geosciences, University of Texas, Austin, TX, USA
| | - C W Haberle
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
| | - E S Howell
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - D R Golish
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - E R Jawin
- Smithsonian Institution National Museum of Natural History, Washington, DC, USA
| | - H H Kaplan
- NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD, USA
| | - L F Lim
- NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD, USA
| | - J L Molaro
- Planetary Science Institute, Tucson, AZ, USA
| | - D Pino Munoz
- Mines ParisTech, PSL Research University, CEMEF-Centre de mise en forme des matériaux, Sophia Antipolis Cedex, France
| | - M C Nolan
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - B Rizk
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - M A Siegler
- Planetary Science Institute, Tucson, AZ, USA
| | - H C M Susorney
- School of Earth Sciences, University of Bristol, Bristol, UK
| | - K J Walsh
- Southwest Research Institute, Boulder, CO, USA
| | - D S Lauretta
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
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10
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Hergenrother CW, Adam CD, Chesley SR, Lauretta DS. Introduction to the Special Issue: Exploration of the Activity of Asteroid (101955) Bennu. JOURNAL OF GEOPHYSICAL RESEARCH. PLANETS 2020; 125:e2020JE006549. [PMID: 33042723 PMCID: PMC7540007 DOI: 10.1029/2020je006549] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 07/02/2020] [Accepted: 07/12/2020] [Indexed: 06/11/2023]
Abstract
Near-Earth asteroid (101955) Bennu is an active asteroid experiencing mass loss. The activity manifests itself in the form of ejection events emitting up to hundreds of millimeter- to centimeter-scale particles. The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer spacecraft monitored particle activity for a 10-month period that included Bennu's perihelion and aphelion. Novel and classical methods were utilized to detect the particles and characterize their orbital and physical properties. Roughly 30% of the observed particle mass escaped to heliocentric orbit. A majority of particles fell back onto the surface of Bennu after ejection, with the longest-lived particle surviving for 6 days on a temporary orbit. Particle ejection events appear to preferentially take place in the afternoon and evening and from low latitudes, although they can occur at any time or latitude. The reaccumulation of material is biased toward low latitudes resulting in the possible in-fill of craters and growth of Bennu's equatorial bulge. Of the potential mechanisms behind this activity that were investigated in focused studies, meteoroid impacts, thermal fracturing, and ricochet-but not water ice sublimation-were found to be consistent with observations. While phyllosilicate dehydration was not investigated with a focused study, it remains a possible mechanism. These mechanisms are not unique to Bennu, suggesting that many near-Earth asteroids may exhibit activity that has gone undetected thus far. Spacecraft missions with wide-field imagers are encouraged to further characterize this phenomenon.
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Affiliation(s)
| | | | - S. R. Chesley
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | - D. S. Lauretta
- Lunar and Planetary LaboratoryUniversity of ArizonaTucsonAZUSA
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11
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Molaro JL, Hergenrother CW, Chesley SR, Walsh KJ, Hanna RD, Haberle CW, Schwartz SR, Ballouz R, Bottke WF, Campins HJ, Lauretta DS. Thermal Fatigue as a Driving Mechanism for Activity on Asteroid Bennu. JOURNAL OF GEOPHYSICAL RESEARCH. PLANETS 2020; 125:e2019JE006325. [PMID: 32999800 PMCID: PMC7507781 DOI: 10.1029/2019je006325] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 07/15/2020] [Accepted: 07/18/2020] [Indexed: 06/11/2023]
Abstract
Many boulders on (101955) Bennu, a near-Earth rubble pile asteroid, show signs of in situ disaggregation and exfoliation, indicating that thermal fatigue plays an important role in its landscape evolution. Observations of particle ejections from its surface also show it to be an active asteroid, though the driving mechanism of these events is yet to be determined. Exfoliation has been shown to mobilize disaggregated particles in terrestrial environments, suggesting that it may be capable of ejecting material from Bennu's surface. We investigate the nature of thermal fatigue on the asteroid, and the efficacy of fatigue-driven exfoliation as a mechanism for generating asteroid activity, by performing finite element modeling of stress fields induced in boulders from diurnal cycling. We develop a model to predict the spacing of exfoliation fractures and the number and speed of particles that may be ejected during exfoliation events. We find that crack spacing ranges from ~1 mm to 10 cm and disaggregated particles have ejection speeds up to ~2 m/s. Exfoliation events are most likely to occur in the late afternoon. These predictions are consistent with observed ejection events at Bennu and indicate that thermal fatigue is a viable mechanism for driving asteroid activity. Crack propagation rates and ejection speeds are greatest at perihelion when the diurnal temperature variation is largest, suggesting that events should be more energetic and more frequent when closer to the Sun. Annual thermal stresses that arise in large boulders may influence the spacing of exfoliation cracks or frequency of ejection events.
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Affiliation(s)
| | | | - S. R. Chesley
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | | | - R. D. Hanna
- Jackson School of GeosciencesUniversity of Texas at AustinAustinTXUSA
| | - C. W. Haberle
- School of Earth and Space ExplorationArizona State UniversityTempeAZUSA
| | - S. R. Schwartz
- Lunar and Planetary LaboratoryUniversity of ArizonaTucsonAZUSA
| | - R.‐L. Ballouz
- Lunar and Planetary LaboratoryUniversity of ArizonaTucsonAZUSA
| | | | - H. J. Campins
- Department of PhysicsUniversity of Central FloridaOrlandoFLUSA
| | - D. S. Lauretta
- Lunar and Planetary LaboratoryUniversity of ArizonaTucsonAZUSA
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