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PLANETARY SCIENCE

A weak and active surface of Bennu

Nature Geoscience volume 15, pages 430–431 (2022)Cite this article

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The surface of the asteroid Bennu is so weakly bonded that rockslide avalanches are easily triggered by small body impacts, and boulders fractured due to diurnal heating and cooling are readily dislodged. The result is a surface under continuous renewal.

The near-Earth asteroid Bennu is entirely covered with boulders and has very low gravity that is only one millionth of Earth’s1. It has been thought that surface morphologies of such a microgravity body are sustained over long timescales because the cohesion force between boulders exceeds that of gravity. Except for occasional collisions of small debris, Bennu was assumed to be a geologically inactive world with neither external nor internal disturbances. However, recent observations by the OSIRIS-REx mission reported by three studies in Nature Geoscience reveal a weak and damaged asteroid surface that is far from stable. Perry et al.2 report evidence of rock avalanches triggered by the deposition of impact ejecta consistent with an extremely low surface strength. Bierhaus et al.3 find from an analysis of the asteroid’s crater population that Bennu’s weak surface is geologically young and may have undergone repeated collisional disruptions. Finally, Delbo et al.4 suggest from analysis of fracture orientations that the boulders have been weakened by thermal fatigue and are easily disrupted by collision of small debris.

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Fig. 1: Bralgah crater on the boulder-covered surface of the asteroid Bennu.

References

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  1. Kobe University, Kobe, Japan

    Masahiko Arakawa

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  1. Masahiko Arakawa
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Correspondence to Masahiko Arakawa.

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Arakawa, M. A weak and active surface of Bennu. Nat. Geosci. 15, 430–431 (2022). https://doi.org/10.1038/s41561-022-00949-8

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