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

D J Scheeres; A S French; P Tricarico; S R Chesley; Y Takahashi; D Farnocchia; J W McMahon; D N Brack; A B Davis; R-L Ballouz; E R Jawin; B Rozitis; J P Emery; A J Ryan; R S Park; B P Rush; N Mastrodemos; B M Kennedy; J Bellerose; D P Lubey; D Velez; A T Vaughan; J M Leonard; J Geeraert; B Page; P Antreasian; E Mazarico; K Getzandanner; D Rowlands; M C Moreau; J Small; D E Highsmith; S Goossens; E E Palmer; J R Weirich; R W Gaskell; O S Barnouin; M G Daly; J A Seabrook; M M Al Asad; L C Philpott; C L Johnson; C M Hartzell; V E Hamilton; P Michel; K J Walsh; M C Nolan; D S Lauretta

doi:10.1126/sciadv.abc3350

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

Sci Adv. 2020 Oct 8;6(41):eabc3350. doi: 10.1126/sciadv.abc3350. Print 2020 Oct.

Authors

D J Scheeres¹, A S French², P Tricarico³, S R Chesley⁴, Y Takahashi⁴, D Farnocchia⁴, J W McMahon², D N Brack², A B Davis², R-L Ballouz⁵, E R Jawin⁶, B Rozitis⁷, J P Emery⁸, A J Ryan⁵, R S Park⁴, B P Rush⁴, N Mastrodemos⁴, B M Kennedy⁴, J Bellerose⁴, D P Lubey⁴, D Velez⁴, A T Vaughan⁴, J M Leonard⁹, J Geeraert⁹, B Page⁹, P Antreasian⁹, E Mazarico¹⁰, K Getzandanner¹⁰, D Rowlands¹⁰, M C Moreau¹⁰, J Small¹¹, D E Highsmith¹¹, S Goossens^{10

12}, E E Palmer³, J R Weirich³, R W Gaskell³, O S Barnouin¹³, M G Daly¹⁴, J A Seabrook¹⁴, M M Al Asad¹⁵, L C Philpott¹⁵, C L Johnson^{3

15}, C M Hartzell¹⁶, V E Hamilton¹⁷, P Michel¹⁸, K J Walsh¹⁷, M C Nolan⁵, D S Lauretta⁵

Affiliations

¹ Smead Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO, USA. [email protected].
² Smead Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO, USA.
³ Planetary Science Institute, Tucson, AZ, USA.
⁴ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
⁵ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA.
⁶ Smithsonian Institution National Museum of Natural History, Washington, DC, USA.
⁷ Planetary and Space Sciences, School of Physical Sciences, The Open University, Milton Keynes, UK.
⁸ Department of Astronomy and Planetary Sciences, Northern Arizona University, Flagstaff, AZ, USA.
⁹ KinetX Aerospace Inc., Simi Valley, CA, USA.
¹⁰ NASA Goddard Space Flight Center, Greenbelt, MD, USA.
¹¹ Aerospace Corporation, Chantilly, VA, USA.
¹² Center for Research and Exploration in Space Science and Technology, University of Maryland, Baltimore County, Baltimore, MD, USA.
¹³ The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA.
¹⁴ The Centre for Research in Earth and Space Science, York University, Toronto, ON, Canada.
¹⁵ Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, Canada.
¹⁶ Department of Aerospace Engineering, University of Maryland, College Park, MD, USA.
¹⁷ Department of Space Studies, Southwest Research Institute, Boulder, CO, USA.
¹⁸ Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France.

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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