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Macroporosity and Grain Density of Rubble Pile Asteroid (101955) Bennu

Biele, Jens and Burke, Keara and Grott, Matthias and Ryan, Andrew and DellaGiustina, D. and Rozitis, Benjamin and Michel, Patrick and Schröder, Stefan and Neumann, Wladimir (2020) Macroporosity and Grain Density of Rubble Pile Asteroid (101955) Bennu. AGU Fall Meeting 2020, 10.12.2020, San Francisco, USA.

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Abstract

Rubble pile asteroids such as (101955) Bennu, the target of NASA’s OSIRIS-REx mission, have large bulk porosities, which are believed to result from void spaces in between the constituent boulders (macroporosity) as well as void spaces within the boulders themselves (microporosity). Instead of estimating both quantities based on comparison with analog meteorites, we use semi-empirical models for the macroporosity of multi-component mixtures (Zou+ 2011, Grott+ 2020) to determine Bennu's macroporosity based on the observed size-frequency distribution of boulders on the surface; global bulk porosity of Bennu was determined from the observed gravity field and shape. The employed size-frequency distribution covers the size range from 0.2 m to 95 m and was obtained by merging local and global particle counting sets. We find that Bennu's macroporosity can be significantly smaller than usually assumed (e.g., (Britt 2002, 2011), as the observed size-frequency distribution allows for an efficient packing of boulders, resulting in a macroporosity of 15± 3 %.. Bennu's high bulk porosity must therefore be a direct consequence of very large boulder microporosity. Furthermore, using estimates of the two main types of boulder microporosity of 52% and 31% as derived from remote-sensing thermal inertia measurements (Rozitis+ 2020), the average grain density in boulders is 2794±250 kg m³, similar to values obtained for CM, CI, and the Tagish lake meteorites. Bennu's bulk porosity corresponding to the above values is 57 %. Bennu’s macroporosity is very similar to that of Ryugu (Grott+ 2020), which we present for comparison.

Item URL in elib:https://elib.dlr.de/139491/
Document Type:Conference or Workshop Item (Speech)
Title:Macroporosity and Grain Density of Rubble Pile Asteroid (101955) Bennu
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Biele, JensJens.Biele (at) dlr.deUNSPECIFIED
Burke, KearaUniversity of Arizona, Tucson AZUNSPECIFIED
Grott, MatthiasMatthias.Grott (at) dlr.deUNSPECIFIED
Ryan, AndrewUniversity of Arizona, Tucson AZUNSPECIFIED
DellaGiustina, D.University of Arizona, Tucson, AZ, USAUNSPECIFIED
Rozitis, BenjaminPlanetary and Space Sciences, Department of Physical Sciences, The Open University, Milton Keynes, UKUNSPECIFIED
Michel, PatrickObservatoire de la Côte d'Azur, CNRS, FranceUNSPECIFIED
Schröder, StefanStefanus.Schroeder (at) dlr.dehttps://orcid.org/0000-0003-0323-8324
Neumann, WladimirWladimir.Neumann (at) dlr.de; Universität HeidelbergUNSPECIFIED
Date:2020
Refereed publication:No
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:Grain Density, Macroporosity
Event Title:AGU Fall Meeting 2020
Event Location:San Francisco, USA
Event Type:international Conference
Event Dates:10.12.2020
Organizer:AGU
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Space Exploration
DLR - Research theme (Project):Vorhaben asteroids and comets (old)
Location: Berlin-Adlershof , Köln-Porz
Institutes and Institutions:Space Operations and Astronaut Training > User center for space experiments (MUSC)
Institute of Planetary Research > Planetary Geology
Institute of Planetary Research > Planetary Physics
Deposited By: Herrmann, Astrid
Deposited On:14 Dec 2020 10:32
Last Modified:04 Mar 2021 11:26

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