2009 Annual Science Report
VPL at University of Washington Reporting | JUL 2008 – AUG 2009
Delivery of Volatiles to Terrestrial Planets
Terrestrial planets are too small to trap gas from the circumstellar disk in which they formed and so must be built from solid materials (rock and ices). In this task, we explore how and when Earth, Mars and other potentially-habitable worlds accumulated water and organic carbon. The main challenge is that water and organic carbon are relatively volatile elements (compared to rock and metal). Therefore, during the period of time in which solids condensed at the current position of Earth, water and carbon would have been mainly in the gas phase. Getting these materials to earth required that inward transportation of material from further out in the disk.
This project entails computational modeling of the planet-formation process. Numerical simulations were run in an attempt to reproduce the inner Solar System, and showed that the key factors are the orbits of Jupiter and Saturn at early times. Out of 40 simulations, none were able to satisfy 5 chosen constraints from the terrestrial planets and asteroid belt. (Raymond et al., 2009). Dynamical models were developed to explore the effect of Oort cloud showers on the Earth (Kaib et al., 2008). Computational models were also used to explore the origin and variation of aluminum-26 abundances in planetary systems. As a short-lived radioactive isotope, Al-26 heats planetesimals shortly after they agglomerate, which has important consequences for the water content of protoplanets and Earth-like planets (Gaidos et al., 2009a,b). Chemical-kinetic models applied to conditions in planet-forming disks are used to explore the carbon-content of planetesimals. A major result is that the dominant condensible form of carbon in protoplanetary disks is in the form of polycyclic aromatic hydrocarbons (PAHs). These compounds are abundant in the interstellar medium, but much less volatile than CO and CO2 and other low-molecular weight carbon-bearing molecules (Kress et al., 2009). Finally, the fate of these PAHs upon atmospheric entry was also explored (Carter et al., 2009; Pevyhouse et al., 2008). A major result here is that as exogenous material enters Earth’s atmosphere, small aromatic compounds will be released at altitudes of 85-110 km. PAHs are excellent absorbers of UV radiation; they may have been effect UV absorbers in the prebiotic atmospheres of habitable planets.
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