Regolith of small asteroids are formed by thermal fatigue

Researchers have revealed that the centimeter-sized fragments and smaller particles that make up the regolith - the layer of loose, unconsolidated rock and dust - of small asteroids is formed by temperature cycling that breaks down rock in a process called thermal fatigue.

Previous studies suggested that the regolith of asteroids one kilometer wide and smaller was made from material falling to the surface after impacts and from boulders that were pulverized by micrometeoroid impacts.

Recent laboratory experiments and impact modeling conducted by a team of researchers from Observatoire de la Cote d'Azur, Hopkins Extreme Materials Institute at Johns Hopkins University, Institut Superieur de l'Aeronautique et de l'Espace and Southwest Research Institute (SwRI) have shown that the debris from large impacts reaches escape velocities and breaks free from the gravitational pull of these asteroids, indicating this mechanism is not the dominant process for regolith creation.

The team's research showed that thermal fragmentation, which is induced by mechanical stresses caused by temperature variations of the rapidly spinning asteroid's short night and day, is the process primarily responsible for breaking up rocks larger than a few centimeters on asteroids.

Model extrapolation of these experiments also showed that thermal fragmentation caused rocks to break down an order of magnitude faster than from micrometeoroid impacts, particularly at distances of 1 astronomical unit (about 93 million miles) with the speed of breakdown slowing at distances further from the Sun.

The paper has been published in Nature Advance Online Publication.