In material sciences, fatigue is a well studied process by which an object is weakened by cyclic loading. It is understood that crack enucleate in zones where the stresses, caused by the loading, concentrate. These cracks can then grow at every loading cycle until they reach a critical length eventually causing the material to fail. Thermal fatigue is due to stresses induced by temperature effects.
Prof. KT Ramesh gave a fundamental contribution in understanding how thermal fatigue damage natural materials in space, in particular on asteroids. With his team, he developed a model that allowed to explain laboratory experiments of temperature cycles on meteorites in order to extrapolate the crack growth measured in the laboratory to the millions of years of asteroid lifetimes.
Recent results from NASA’s OSIRIS-REx sample-return space mission to the asteroid Bennu, shows that this asteroid is covered with boulders with sizes ranging from tens of meters down to the limiting spatial resolution of the instrument of some cm per pixel. Some of these boulders show presence of cracks, other appear to have through-going fractures and fracture networks, but no clear sign of impact causing these cracks. There are also groups of boulders whose morphology is consistent with in situ desegregation of a parent boulder. These features indicate that thermal fatigue is an important process shaping the surface of this asteroid, confirming predictions that Prof. KT Ramesh put forward some years earlier.