Interaction of energetic particles and dust grains with asteroidal surfaces

Low energy solar wind (SW) and solar energetic particles (SEP) interact wit h material exposed on the surface of planetary objects devoid of an atmosph ere and a global magnetic field such as the Moon and the asteroids. Microme teoroid impacts will produce microcraters on samples exposed on the surface s of these bodies and also cause microscale erosion and at times catastroph ic rupture of the target rocks and soil grains. The impacting flux of meteo roids thus controls the effective SW and SEP exposure durations of samples on the lunar and asteroidal surfaces. The lunar samples contain abundant re cords of energetic particle interactions and micrometeoroid impacts while s uch records found in gas-rich meteorites can be considered to be representa tive of asteroidal samples. These records allow us to infer the composition and intensity of SW and SEP in the past as well as surface dynamical proce sses operating on the Moon and asteroids at different epochs. However, unli ke the lunar records that span the time interval from the present to severa l billion years in the past, the asteroidal (gas-rich meteorite) records pr ovide information only for some distant epochs in the past. We do not have much information about the contemporary energetic particle and dust grain e nvironment in the asteroidal region, The Muses-C mission, that will bring b ack near surface samples from an asteroid, will be extremely important in t his regard.