Chemistry of comets and other ice-bearing planetesimals

Abstract

Overview Ices, composed of water and other volatile compounds, are a very important component of the solar system. Whether formed by condensation in the nebula or imported from the interstellar medium, these frozen substances accreted with dust and rock beyond the snowline to form vast swarms of planetesimals and some larger bodies. Most of the ice-bearing planetesimals have been swept out of the planetary region by gravitational interactions with the giant planets, and their distribution now extends out to the limits of the Sun's grasp. Occasionally these bodies careen into the inner solar system, where sunlight volatilizes their ices, revealing them to be comets. Other planetesimals that formerly contained ices have remained near their formation locations in the asteroid belt; most of these suffered aqueous alteration when ices were melted. In this chapter we consider what has been discovered about the chemistry of comets and hydrated asteroids. The importance of these objects to cosmochemistry is a consequence of their primitive compositions and remarkable state of preservation. Icy bodies in the solar system In Chapter 10, we briefly considered ices and how they trap noble gases and provide sites for the formation of organic matter in the ISM and the solar nebula. We now discuss the ices themselves, including how they originated, where they existed in the early solar system and where they exist today.