But scientific priorities should also be a major consideration. Progress in answering these questions requires several simultaneous approaches. On the ground, research and analysis with telescopes and theoretical models can improve our understanding. In space, small spacecraft like the upcoming Discovery series can pursue limited objectives while large ones like the Cassini mission to Saturn aim at comprehensive goals. We have recently been heading a National Research Council committee that sought to answer this question.
Comets are the best-preserved remnants of the material from which the solar system formed.
These primitive bodies may also contain the biogenic elements and compounds with which the primordial Earth was endowed. Comets, and especially their pristine interiors, have received little detailed scrutiny so far, despite their potential to shed light on the origin of the solar system. Mars holds special interest because it may help unlock many secrets of our own world. Although the planet is cold and dry today, its atmosphere seems to have been denser and wetter eons ago. Indeed, its past climate may have been so benign that the planet could provide a unique perspective on the origins of life.