The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. CitationHamilton, V.E., et al., "Evidence for widespread hydrated minerals on asteroid (101955) Bennu." Nature astronomy 3, 4 (2019): p.

Christensen, P. R.; Drouet d'Aubigny, C. Y.; Hamilton, V. E.; Reuter, D. C.; Rizk, B.; Simon, A. A.; Asphaug, E.; Bandfield, J. L.; Barnouin, O. S.; Barucci, M. A.; Bierhaus, E. B.; Binzel, R. P.; Bottke, W. F.; Bowles, N. E.; Campins, H.; Clark, B. C.; Clark, B. E.; Connolly, H. C.; Daly, M. G.; Leon, J. de; Delbo', M.; Deshapriya, J. D. P.; Elder, C. M.; Fornasier, S.; Hergenrother, C. W.; Howell, E. S.; Jawin, E. R.; Kaplan, H. H.; Kareta, T. R.; Le Corre, L.; Li, J.-Y.; Licandro, J.; Lim, L. F.; Michel, P.; Molaro, J.; Nolan, M. C.; Pajola, M.; Popescu, M.; Garcia, J. L. Rizos; Ryan, A.; Schwartz, S. R.; Shultz, N.; Siegler, M. A.; Smith, P. H.; Tatsumi, E.; Thomas, C. A.; Walsh, K. J.; Wolner, C. W. V.; Zou, X.-D. and Lauretta, D. S. (2019). Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis. Nature Astronomy, 3 pp. 341-351. For guidance on citations see FAQs.Length of main text: 2956 words Length of methods: 3605 words Length of legends: 565 words Number of references: 53 main text, 69 including methods and supplementary information (refs 67 to 69 are cited in the SI only) , we show that asteroid (101955) Bennu's surface is globally rough, dense with boulders and low in albedo. The number of boulders is surprising given Bennu's moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennu's surface particles span from the disruption of the asteroid's parent body (boulders) to recent in situ production (micron-scale particles).

The Open University's repository of research publications and other research outputs The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements

During its approach to asteroid (101955) Bennu, NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed Bennu’s immediate environment, photometric properties, and rotation state. Discovery of a dusty environment, a natural satellite, or unexpected asteroid characteristics would have had consequences for the mission’s safety and observation strategy. Here we show that spacecraft observations during this period were highly sensitive to satellites (sub-meter scale) but reveal none, although later navigational images indicate that further investigation is needed. We constrain average dust production in September 2018 from Bennu’s surface to an upper limit of 150 g s –1 averaged over 34 min. Bennu’s disk-integrated photometric phase function validates measurements from the pre-encounter astronomical campaign. We demonstrate that Bennu’s rotation rate is accelerating continuously at 3.63 ± 0.52 × 10 –6 degrees day –2 , likely due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, with evolutionary implications.

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.