How Metallicity Affects Volatile Abundances: Implications for Planetary System Formation
Abstract
Astronomers have confirmed the existence of several thousand extra-solar planetary systems having a wide range of orbital and compositional characteristics. A host star's metallicity, defined as the abundance of all elements heavier than helium (metals), appears to play a role in determining whether an exoplanetary system is more likely to include Jupiter-sized gas and ice giants. Here we show how molecular cloud metallicity is likely to significantly affect the initial conditions of planetary formation by affecting the abundances of volatile ices (H2O, CO, etc.) in parent molecular clouds. Through analytic and numerical treatments of molecular chemical lifetimes, we show that metal-poor clouds are likely to be significantly depleted in volatile ices compared to relatively metal-rich ones, with metal-rich molecular clouds ([Fe/H]>0.5) likely to have a larger fraction of their volatile elements in the form of ices the surfaces of dust grains compared to metal poor ( [Fe/H] <0.5) ) ones. These correlations have significant implications for planetary system formation. For example, we evaluate how higher volatile ice abundances shift the radial position of volatile ice snowlines. Volatile abundances may also significantly affect the characteristic timescales for planetesimal growth by affecting their dust-dust collision sticking coefficients. Using a simple model of ice-vapor equilibrium, we quantitatively evaluate under what conditions the "wet Earth" hypothesis for the origins of Earth's water is feasible. Our modeling suggests that a partial monolayer (∼ 2%) of water on interstellar dust grain surfaces with MRN distribution would provide the Earth with enough water to account for its contemporary oceans.
- Publication:
-
American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23526103D