Snow Lines and Protoplanetary Disks, Or, Where’d All The Water Go?

Planet formation theory predicts a water-rich Earth. On a comparative basis, the Earth is water-poor. This paper aims to reconcile theory and observation.Categories: Daily paper summaries(Click to read more...)

Paper Title: On The Evolution of the Snow Line in Protoplanetary Disks (arxiv: 1207.4284)
Authors: R. G. Martin, M. Livio
First Author’s Affiliation: Space Telescope Science Institute, Baltimore, USA
Journal: Monthly Notices of the Royal Astronomical Society (accepted)

Introduction
This paper aimed at addressing a puzzle in planet formation theory: why is the Earth so water-poor?
We often talk about the Earth as a water-rich planet; in fact, when astronomers refer to Earth-like planets, we generally mean worlds capable of hosting liquid water. However, in comparison to the gas giants, Earth is very water poor! The Earth is only .023% water by mass, while the outer solar system giants are as much as 40% water.
The explanation usually invoked to explain this is the “ice line”. At the beginning of the solar system, planets condensed from a disk of gas, dust and other materials circling the Sun; this is referred to as the “protoplanetary disk“. Beyond a certain distance from the Sun, ice in the disk condensed into ice; within it, ...