2012 Annual Science Report
VPL at University of Washington Reporting | SEP 2011 – AUG 2012
Delivery of Volatiles to Terrestrial Planets
We are investigating the mechanisms by which terrestrial planets obtain water and organic compounds. By understanding how these crucial constituents for life came to Earth, we can determine whether these mechanisms also operate in exoplanetary systems. When an earth-like planet is finally discovered in an exoplanetary system, it will be difficult to directly measure the composition of that planet. However, VPL scientists will use the observable properties of the system to determine whether that planet has a history that allowed water and organics to have been transported to it. One of the important questions is the initial state of the organic compounds, which sets stringent limits on the ability of the earth-like planets to acquire carbon.
Last year, 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-then-outward migration of Jupiter in the gaseous protoplanetary disk. If Jupiter’s turnaround point (“tack”) was 1.5 AU then Earth’s water was delivered by material that remains as today’s C-type asteroids. This material had itself been implanted into the asteroid belt from beyond Jupiter’s orbit. This year, Raymond and collaborators used the Grand Tack model to investigate extrasolar planetary systems. They found that although a wide variety of terrestrial planet compositions are produced, planets with Earth-like compositions should be common within extrasolar planetary systems.
The other aspect of this task focuses on how habitable planets obtain volatiles, particularly carbon. Co-I Kress’ undergraduate researcher Tin Tran (in collaboration with J. Chiar of the SETI Institute and her colleagues) found that polycyclic aromatic hydrocarbons (PAHs) with 10-49 carbon atoms predominate over larger PAHs in star forming regions. This is an important discovery because it sets constraints on the initial composition of the carbon compounds that carried organics to the Earth. Star- and planet-formation environments seem to be conducive to breaking down PAHs into smaller (and more volatile) species; thus, these early results may lead to additional constraints being placed on the timescales and source regions for the delivery of carbon to habitable planets.
PROJECT INVESTIGATORS:Monika Kress
PROJECT MEMBERS:Rory Barnes
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Indirect and direct astronomical observations of extrasolar habitable planets.
Sources of prebiotic materials and catalysts
Earth's early biosphere.
Effects of extraterrestrial events upon the biosphere