nai

Project Progress

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.