Abstract
Low energy solar wind (SW) and solar energetic particles (SEP) interact with material exposed on the surface of planetary objects devoid of an atmosphere and a global magnetic field such as the Moon and the asteroids. Micrometeoroid impacts will produce microcraters on samples exposed on the surfaces of these bodies and also cause microscale erosion and at times catastrophic rupture of the target rocks and soil grains. The impacting flux of meteoroids thus controls the effective SW and SEP exposure durations of samples on the lunar and asteroidal surfaces. The lunar samples contain abundant records of energetic particle interactions and micrometeoroid impacts while such records found in gas-rich meteorites can be considered to be representative 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 processes operating on the Moon and asteroids at different epochs. However, unlike the lunar records that span the time interval from the present to several billion years in the past, the asteroidal (gas-rich meteorite) records provide information only for some distant epochs in the past. We do not have much information about the contemporary energetic particle and dust grain environment in the asteroidal region. The Muses-C mission, that will bring back near surface samples from an asteroid, will be extremely important in this regard.
