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The unexpected surface of asteroid (101955) Bennu.
D S Lauretta1, D N DellaGiustina2, C A Bennett2
1Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA. lauretta@orex.lpl.arizona.edu.
Nature
|March 21, 2019
Summary
NASA's OSIRIS-REx mission found asteroid Bennu has a diverse surface, unlike predictions. This unexpected terrain presents challenges for returning pristine samples of this primitive, volatile-rich asteroid.
Area of Science:
- Planetary Science
- Astrogeology
- Astrochemistry
Background:
- Asteroid Bennu is a primitive B-type asteroid, a potential source of prebiotic molecules and water on Earth.
- Bennu's organic-rich, hydrated composition is linked to carbonaceous chondrites, but meteorites are altered.
- The OSIRIS-REx mission aims to return a pristine sample of Bennu, unaffected by terrestrial contamination.
Purpose of the Study:
- To compare early OSIRIS-REx observations of Bennu with pre-encounter expectations.
- To assess the feasibility of returning a pristine sample from Bennu.
- To understand Bennu's surface properties and their implications for sample collection.
Main Methods:
- Utilized the OSIRIS-REx spacecraft's instrument suite for global characterization.
- Performed high-resolution imaging to document surface properties at sub-centimeter scale.
- Analyzed early observational data against pre-encounter models of Bennu's surface.
Main Results:
- Bennu's bulk composition is hydrated and volatile-rich, aligning with expectations.
- Surface imaging revealed unexpected diversity in albedo, texture, particle size, and roughness, exceeding mission design specifications.
- Pre-encounter models predicted a smoother surface with centimeter-scale particles, contrasting with observed heterogeneity.
Conclusions:
- The diverse and rough surface of Bennu presents significant challenges for the planned sampling strategy.
- Identifying hazard-free sampling sites of sufficient size (5-20 meters) is more difficult than anticipated.
- Mission success in obtaining a pristine sample is challenged by the unexpected nature of Bennu's surface.
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