Heterogeneous mass distribution of the rubble-pile asteroid (101955) Bennu

Scheeres, D. J.; French, A. S.; Tricarico, P.; Chesley, S. R.; Takahashi, Y.; Farnocchia, D.; McMahon, J. W.; Brack, D. N.; Davis, A. B.; Ballouz, R.-L.; Jawin, E. R.; Rozitis, B.; Emery, J. P.; Ryan, A. J.; Park, R. S.; Rush, B. P.; Mastrodemos, N.; Kennedy, B. M.; Bellerose, J.; Lubey, D. P.; Velez, D.; Vaughan, A. T.; Leonard, J. M.; Geeraert, J.; Page, B.; Antreasian, P.; Mazarico, E.; Getzandanner, K.; Rowlands, D.; Moreau, M. C.; Small, J.; Highsmith, D. E.; Goossens, S.; Palmer, E. E.; Weirich, J. R.; Gaskell, R. W.; Barnouin, O. S.; Daly, M. G.; Seabrook, J. A.; Al Asad, M. M.; Philpott, L. C.; Johnson, C. L.; Hartzell, C. M.; Hamilton, V. E.; Michel, P.; Walsh, K. J.; Nolan, M. C. and Lauretta, D. S. (2020). Heterogeneous mass distribution of the rubble-pile asteroid (101955) Bennu. Science Advances, 6(41), article no. eabc3350.

DOI: https://doi.org/10.1126/sciadv.abc3350

Abstract

The gravity field of a small body provides insight into its internal mass distribution. We used two approaches to measure the gravity field of the rubble-pile asteroid (101955) Bennu: (i) tracking and modeling the spacecraft in orbit about the asteroid and (ii) tracking and modeling pebble-sized particles naturally ejected from Bennu’s surface into sustained orbits. These approaches yield statistically consistent results up to degree and order 3, with the particle-based field being statistically significant up to degree and order 9. Comparisons with a constant-density shape model show that Bennu has a heterogeneous mass distribution. These deviations can be modeled with lower densities at Bennu’s equatorial bulge and center. The lower-density equator is consistent with recent migration and redistribution of material. The lower-density center is consistent with a past period of rapid rotation, either from a previous Yarkovsky-O’Keefe-Radzievskii-Paddack cycle or arising during Bennu’s accretion following the disruption of its parent body.

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