Planetary Science

Shock-Buffering Asteroid

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Science  07 Feb 2014:
Vol. 343, Issue 6171, pp. 580
DOI: 10.1126/science.343.6171.580-c
CREDIT: M. ZHU ET AL., GEOPHYS. RES. LETT. 40, 24 (28 DECEMBER 2013) © 2014 AMERICAN GEOPHYSICAL UNION

The stereotype of an asteroid as a rigid monolith has been dispelled numerous times when spacecraft have allowed closer inspection: Many of these minor planets look more like fluffy piles of rubble. The second Chinese lunar probe, Chang'E-2, explored the asteroid Toutatis (4179) in a December 2012 flyby, and Zhu et al. report evidence that the body has endured repeated impact shocks that were attenuated by compression of its porous regolith. One 800-m crater seen near the south pole of Toutatis (∼4.5 km long) implies an impactor of sufficient energy to have shattered a solid asteroid. However, if this collection of material is already fractured, it is more resilient to dramatic impact. The impact energy flows through the body as seismic shaking that resettles the surface and erases smaller craters, which are indeed deficient in number as compared to expectations. Further support for seismic resurfacing may lie in boulders observed on the “neck” of Toutatis, where such larger fragments experiencing shaking would eventually rattle to the surface. The authors believe that these also imply that the bi-lobed body is the result of a low-velocity sticking collision that initially damaged the impact surface and then slowly excavated the boulders.

Geophys. Res. Lett. 10.1002/2013GL058914 (2013).

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