2011 Annual Science Report
VPL at University of Washington Reporting | SEP 2010 – AUG 2011
Delivery of Volatiles to Terrestrial Planets
This project uses computer models and laboratory work to better understand how volatile materials that are important for life, like water, methane, and other organic molecules, are delivered to terrestrial planets. Habitable planets are too small to gravitationally trap these volatiles directly from the gas disk from which they formed, and instead they must be delivered as solids or ices at the time of the planet’s formation, or ongoing as the planet evolves. These trapped volatiles are eventually released to form our oceans and atmosphere. In this task we use computer models of planet formation and migration to understand how the asteroid belt, which is believed to be the source of the Earth’s oceans, was formed. We also use models to understand what happens to meteoritic material as it enters a planet’s atmosphere, especially where it gets deposited in the atmosphere, what happens to it chemically, and how it interacts with the light from the parent star. .
Co-I Sean Raymond and his collaborators proposed a new model for the early evolution of the Solar System — called the “Grand Tack” — that is characterized by the inward-thenoutward migration of Jupiter in the gaseous protoplanetary disk. If Jupiter’s turnaround point (“tack”) was 1.5 AU then our model can explain both the masses and orbital distribution of the terrestrial planets (including Mars) and the S-type vs C-type dichotomy of the asteroid belt. In the context of this model, Earth’s water was delivered by C-type material from beyond Jupiter’s orbit, that was first implanted into the asteroid belt as part of the migration process.
For much of the year, we have been investigating the fate of meteoritic, organic compounds upon atmospheric entry. We previously found that as exogenous material enters Earth’s atmosphere, organic compounds – including methane, phenol, and styrene – are released at altitudes of 85-110 km. These compounds then undergo reactions in the upper atmosphere that form a more complex molecule containing a para-disubstituted aromatic ring. We extended these studies to explore the entry of organic, meteoric compounds into the atmospheres of other earth-sized planets (masses from 0.1 to 10 Earth masses, and 0.1 to 10 times the earth’s atmospheric pressure). Based on this line of research, we found that the critical factor in the survival of exogenous organics is the altitude at which the material is released. In order to survive, organic material must be released beneath a sufficient amount of atmosphere to block incoming stellar UV. Thus, the stellar UV flux (which is highly dependent on stellar mass rather than planetary properties) is a key factor in determining the fate of incoming organics on earth-like planets. Titan-like planets, i.e those with low masses and thick atmospheres, result in a low-velocity infall, much slower heating rate, and better survival of exogenous organic compounds. Ultimately, detailed atmospheric profiles are critical to determining the altitude at which organics get released during entry.
PROJECT INVESTIGATORS:Monika Kress
PROJECT MEMBERS:Rory Barnes
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Sources of prebiotic materials and catalysts
Earth's early biosphere.
Effects of extraterrestrial events upon the biosphere