The Formation of Life-sustaining Planets in Extrasolar

Introduction: One of the characteristics that makes Earth a suitable environment for the origin of life is the presence of significant amounts of water and other volatile materials. It is thought that Earth formed by the accretion of a large number of small, rocky planetesimals which formed in the inner part of the Sun’s protoplanetary nebula (Wetherill 1990). However, protoplanetary nebula models indicate that planetesimals forming at 1 AU from the Sun would have been very dry, containing little or no volatile material (Cassen 2001). This suggests that Earth obtained most of its volatiles by accreting planetesimals that formed elsewhere in the nebula. These planetesimals would have been driven onto Earth-crossing orbits by gravitational perturbations from the giant planets, principally Jupiter and Saturn.