Low thermal inertia of carbonaceous asteroid Bennu driven by cracks observed in returned samples

Thermal inertia is used to infer physical properties of asteroid surfaces. The carbonaceous asteroid Bennu has low thermal inertia suggestive of a surface covered in sub-centimeter rock fragments. However, spacecraft observations revealed that Bennu is instead blanketed by boulders of differing physical properties, with the most abundant population displaying very low thermal inertia compared to carbonaceous chondritic meteorites. Here we show that morphologically distinct particles in samples returned from Bennu also possess distinct thermal and physical properties, consistent with their genetic connection to the boulders. Angular particles have higher thermal inertia, greater hardness, and fewer but longer cracks that lead to more efficient splitting, relative to the hummocky particles. A hummocky particle exhibits low thermal inertia at sub-millimeter scales due to fine pores. Tortuous crack networks in hummocky particles further reduce thermal inertia while resisting disaggregation. Samples from Ryugu, a carbonaceous asteroid with similarly low thermal inertia, have cracks like those in Bennu's hummocky particles yet have bulk densities that indicate lower porosity. These observations imply that the low thermal inertia of both asteroids is driven by cracks in rocks resulting from geological processes within the parent body or, more recently, micrometeoroid impacts and thermal fatigue.

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Publication Details

Journal
Nature Communications
Published
2026-03-17
DOI
https://doi.org/10.1038/s41467-026-68505-1
Primary Topic
Astro and Planetary Science
Type
article
Field-Weighted Citation Impact
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article

Low thermal inertia of carbonaceous asteroid Bennu driven by cracks observed in returned samples

R.-L. Ballouz, C. Calva, A. J. Ryan, A. R. Hildebrand et al.
Nature Communications
Astro and Planetary Science
article

Low thermal inertia of carbonaceous asteroid Bennu driven by cracks observed in returned samples

R.-L. Ballouz, C. Calva, A. J. Ryan, A. R. Hildebrand, J. Plummer, T. J. Zega, J. P. Dworkin, E. R. Jawin, P. Sánchez, P. Haenecour, M. A. Siegler, M. Montoya, F. Cheng, D. S. Lauretta, D. N. DellaGiustina, H. C. Connolly, C. W. V. Wolner, J. J. Barnes, J. Freemantle, K. Ishimaru, S. Cambioni, D. H. Hill, N. Sakatani, M. K. Kontogiannis, P. F. Schofield, E. L. Berger, S. J. Tanaka, C. P. Opeil, A. Alasli, N. G. Lunning, A. J. King, J. L. Molaro, H. C. Bates, R. J. Macke, F. Tusberti, C. Gonzalez, T. J. McCoy, R. Fujita, H. Nagano, E. B. Bierhaus, M. Pajola, J. P. Emery, C. G. Hoover, V. E. Hamilton, R. Harrington, C. M. Elder, R. D. Hanna, S. A. Eckley, K. Righter, M. Delbo, J. Biele, E. W. O’Neal, K. Jardine, T. Ishizaki, L. T. J. Hanton, D. P. Glavin
article en

Abstract

Thermal inertia is used to infer physical properties of asteroid surfaces. The carbonaceous asteroid Bennu has low thermal inertia suggestive of a surface covered in sub-centimeter rock fragments. However, spacecraft observations revealed that Bennu is instead blanketed by boulders of differing physical properties, with the most abundant population displaying very low thermal inertia compared to carbonaceous chondritic meteorites. Here we show that morphologically distinct particles in samples returned from Bennu also possess distinct thermal and physical properties, consistent with their genetic connection to the boulders. Angular particles have higher thermal inertia, greater hardness, and fewer but longer cracks that lead to more efficient splitting, relative to the hummocky particles. A hummocky particle exhibits low thermal inertia at sub-millimeter scales due to fine pores. Tortuous crack networks in hummocky particles further reduce thermal inertia while resisting disaggregation. Samples from Ryugu, a carbonaceous asteroid with similarly low thermal inertia, have cracks like those in Bennu's hummocky particles yet have bulk densities that indicate lower porosity. These observations imply that the low thermal inertia of both asteroids is driven by cracks in rocks resulting from geological processes within the parent body or, more recently, micrometeoroid impacts and thermal fatigue.

Nature CommunicationsVol. 17(1)
Boston College (US), University of Hawaiʻi at Mānoa (US), Lockheed Martin (United States) (US), Southwest Research Institute (US), Centre National de la Recherche Scientifique (FR), Planetary Science Institute (US), Goddard Space Flight Center (US), Jet Propulsion Laboratory (US), Natural History Museum (GB), American Museum of Natural History (US), National Museum of Natural History (US), University of Arizona (US), Johns Hopkins University (US), University of Calgary (CA), University of Colorado Boulder (US), York University (CA), Université Côte d'Azur (FR), Northern Arizona University (US), Japan Aerospace Exploration Agency (JP), Vatican Secret Archives (VA), Alberta Energy (CA), Johns Hopkins University Applied Physics Laboratory (US), Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR) (DE), Observatoire de la Côte d’Azur (FR), National Air and Space Museum (US), Johnson Space Center (US), Osservatorio Astronomico di Padova (IT), Rowan University (US), University of Rochester (US), Arizona State University (US), Nagoya University (JP), Massachusetts Institute of Technology (US), The University of Texas at Austin (US)
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Astro and Planetary Science
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