The role of comets and asteroids in solar-system development - space exploration

Exploration by space missions of the near-nucleus regions of comets Halley and Grigg-Skjellerup has resulted in valuable but expensive snapshots of cometary phenomena. The 'ground truth' from such missions, which can be established only by this means of dedicated space exploration, provides essential inputs to models of cometary processes. It also gives calibration data for a very wide base of cometary and asteroidal observations, past, present and future. Seen as objects which are both eroded by impacts from interplanetary dust and also the progenitors of interplanetary dust, we find both asteroids and comets are needed to contribute to this population. Contrary to expectations, as new data on the asteroids and comets is analysed, Rie find the differences between the two classes of primordial body is very much less distinct; accounting for the interplanetary distribution and properties of dust mass requires not only both classes of object but also a distribution of mixed classes. ESA's newly selected cometary mission Rosetta will offer a unique opportunity, during a rendezvous encounter from aphelion to perihelion, for the extended and detailed in situ observations of a target comet. It will also act as a valuable focus on the nature and role of comets in both the origin and development of the Solar System.