P037-07
The Gravity and Geophysical Properties of (101955) Bennu
Thursday, 10 December 2020: 07:24
Virtual
Daniel Jay Scheeres1, Andrew French2, Pasquale Tricarico3, Steven R Chesley4, Yu Takahashi5, Davide Farnocchia6, Jay McMahon7, Daniel N Brack2, Alex Benjamin Davis1, Ronald -L Ballouz8, Erica R Jawin9, Ben Rozitis10, Joshua P Emery11, Andrew J Ryan12, Ryan S Park6, Brian Rush13, Nickolaos Mastrodemos13, Brian Kennedy14, Julie Bellerose13, Daniel P Lubey13, Dianna Velez13, Andrew Vaughan5, Jason Leonard15, Jeroen Geeraert16, Brian R. Page16, Peter G Antreasian17, Erwan Mazarico18, Kenneth M Getzandanner19, David D Rowlands20, Michael Moreau21, Jeffrey Small22, Dolan E Highsmith23, Sander J Goossens24, Eric E Palmer3, John R Weirich3, Robert W Gaskell25, Olivier S Barnouin26, Michael G Daly27, Jeff Seabrook28, Manar Al Asad29, Lydia Philpott30, Catherine Johnson31, Christine M Hartzell32, Victoria E Hamilton33, Patrick Michel34, Kevin John Walsh35, Michael C Nolan36 and Dante S Lauretta12, (1)University of Colorado Boulder, Ann and H.J. Smead Department of Aerospace Engineering Sciences, Boulder, CO, United States, (2)University of Colorado at Boulder, Ann and H.J. Smead Department of Aerospace Engineering Sciences, Boulder, United States, (3)Planetary Science Institute, Tucson, AZ, United States, (4)Jet Propulsion Laboratory, Pasadena, CA, United States, (5)Jet Propulsion Laboratory, Pasadena, United States, (6)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (7)University of Colorado at Boulder, Ann and H.J. Smead Department of Aerospace Engineering Sciences, Boulder, CO, United States, (8)University of Arizona, Tucson, United States, (9)Brown University, Providence, RI, United States, (10)Open University, Milton Keynes, United Kingdom, (11)Univ of Tennessee-EPS, Knoxville, TN, United States, (12)University of Arizona, Lunar and Planetary Laboratory, Tucson, AZ, United States, (13)NASA Jet Propulsion Laboratory, Pasadena, United States, (14)JPL/NASA/Caltech, Pasadena, CA, United States, (15)KinetX Space Navigation & Flight Dynamics Practice, Denver, CO, United States, (16)KinetX Inc, Tempe, AZ, United States, (17)KinetX Inc, Tempe, United States, (18)Massachusetts Institute of Technology, Greenbelt, MD, United States, (19)NASA GSFC, Greenbelt, MD, United States, (20)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (21)NASA Goddard Space Flight Center, Greenbelt, United States, (22)Aerospace Corporation Chantilly, Chantilly, United States, (23)Aerospace Corporation, Greenbelt, MD, United States, (24)NASA GSFC / UMBC CRESST, Greenbelt, MD, United States, (25)Planetary Science Institute Tucson, Tucson, AZ, United States, (26)JHU Applied Physics Lab, Laurel, MD, United States, (27)York University, Centre for Research in Earth and Space Science, Toronto, ON, Canada, (28)York University, Toronto, ON, Canada, (29)University of British Columbia, Department of Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada, (30)University of British Columbia, Vancouver, Canada, (31)University of British Columbia, Vancouver, BC, Canada, (32)University of Maryland College Park, College Park, MD, United States, (33)Southwest Research Institute Boulder, Boulder, CO, United States, (34)UNS-CNRS-Observatoire de la Cote d'Azur, Laboratoire Lagrange, NIce, France, (35)University of Melbourne, Parkville, Australia, (36)Arecibo Observatory, Arecibo, PR, United States
Abstract:
We report estimates of asteroid (101955) Bennu’s gravity. In addition to classical radio science techniques for estimating a body's gravity field coefficients, the discovery of particles ejected from Bennu that persist in orbit for multiple revolutions [1] provided a unique opportunity to probe the gravity field to higher degree and order than otherwise possible. Several aspects of the environment are highly sensitive to the gravity field and have changed from earlier results [2, 3, 4].
We compare the estimated gravity field solutions with the constant density shape model to constrain models of the internal density variation. We find that these differences are consistent with an under-dense core and equatorial ridge.
An under-dense equator could be consistent with transport of material to the equator without compaction. Given the slope transition at the Roche lobe, this would also be consistent with the ballistic transport of material into the equatorial region. Estimates of the rate of particle migration do not seem to be enough to account for the overall equatorial bulge of Bennu, however, implying that this feature could be older and not due to the more recent transport of material to the equator.
The lower-density interior is consistent with a period of rapid spin and failure of the interior of the body. This could also be consistent with the raised equatorial bulge. This interior failure could have occurred in an earlier epoch of YORP-induced rapid rotation or could trace to the initial formation of Bennu as a distinct rubble-pile body. Tests of this hypothesis require additional simulations of how rubble-pile asteroids coalesce after the catastrophic disruption of their parent body.
Acknowledgements: This material is based upon work supported by NASA under Contract NNM10AA11C issued through the New Frontiers Program. Part of this research was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. We are grateful to the entire OSIRIS-REx Team for making the encounter with Bennu possible.
References: [1] Lauretta D.S. & Hergenrother C.W. et al. (2019) Science 366, eaay3544. [2] Scheeres D.J. et al. (2019) Nature Astronomy 3, 352-361. [3] Barnouin O.S. et al. 2019. Nature Geoscience 12, 247-252. [4] Tricarico P. et al. (2019) EPSC-DPS Abstract #2019-547-1.
