Cracking Rocks on Bennu with Sunlight

Image credit: NASA’s Goddard Space Flight Center/University of Arizona

Images from NASA’s OSIRIS-REx (Origins Spectral Interpretation Resource Identification Security-Regolith Explorer) spacecraft show that rocks on the surface of asteroid Bennu may crack and break down due to thermal cycling from sunlight. Repeated heating and cooling through the extreme temperature differences between day and night on Bennu can cause stress, fatigue, and cracking in the rocks in a process called thermal fracturing or exfoliation. As reported in a study led by Jamie Molaro of the Planetary Science Institute, OSIRIS-REx Camera Suite (OCAMS) images show that boulder morphologies observed on Bennu are consistent with terrestrial rock features caused by thermal fracturing. Scientists have hypothesized that thermal fracturing could be an important weathering process and means of regolith production contributing to the evolution of planetary surfaces, particularly airless bodies, in the solar system. However, such processes had not yet been definitively observed on any airless body. These in-situ observations, coupled with future laboratory measurements of samples returned by OSIRIS-REx in 2023, will help scientists better understand how the process of thermal fracturing works on airless bodies. How thermal fracturing evolves the surfaces of airless bodies may affect other observable characteristics such as spectral signatures, surface roughness, thermal inertia, and subtle non-gravitational accelerations on their rotation states and orbits. READ MORE