Internal Cracks Explain Bennu's Rugged Surface

The article discusses the reasons behind the discrepancy between Earth-based observations and the actual surface characteristics of asteroid Bennu, as revealed by the OSIRIS-REx spacecraft. While initial observations suggested a surface comprised of small rock fragments, OSIRIS-REx found a surface dominated by large boulders. The study attributes this to internal cracks within the rocks, which result in low thermal inertia. These cracks are believed to be caused by thermal fatigue due to Bennu's rapid rotation and constant temperature swings, as well as micrometeoroid impacts. The findings challenge the reliability of Earth-based observations for characterizing asteroid surfaces and emphasize the importance of direct spacecraft analysis. The study also draws parallels with asteroid Ryugu, which exhibits similar characteristics. The analysis of returned samples from Bennu and Ryugu provides valuable ground-truthing for remote-sensing data. The researchers hypothesize that Bennu formed from a parent body that was struck long ago, resulting in chunks breaking off into space and eventually coalescing to form the asteroid. The low rotation time of 4.3 hours contributes to the thermal stress experienced by the rocks on the surface.

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