NASA Astrobiology Institute (NAI)

In this task, we use computer models of the formation of terrestrial planets and the chemistry in the protoplanetary disk to better understand how carbon, the backbone of life processes, becomes incorporated into forming planets. Our planet formation models are also being used to understand planet formation around low-mass stars and binary stars, and how tidal interactions between planet and star can cause a planet’s orbit to evolve over time, potentionally taking it into, or out of, the habitable zone.

We have extended models of terrestrial planet formation to new domains such as around low-mass stars and binary stars. We are developing a new model for the origin of carbon on the Earth and other habitable planets, based on studies of meteoritics, protoplanetary disk structure, and planetary accretion. We have also studied the long-term tidal-orbital evolution of habitable zone planets around low-mass stars, and found that in some cases planets may form in the habitable zone but evolve in to hotter orbits because of tidal effects. We have studied the formation of close-in terrestrial planets (e.g., “super-Earths”) and have shown that with high-precision transit and radial velocity information it may be possible to uniquely determine the formation mechanism. We have studied the dynamics of extra-solar planetary systems – in 2007 we were the first to successfully predict the mass and orbit of an exoplanet. We continue to develop new models for the formation and evolution of planets both in our own solar system and around other stars.

& Raymond 2008, ApJ)">

Fig 1. hd74156.orbcomp.full.jpg — Left: Orbits of the planets in the HD 74156 planetar system, and the zone predicted by VPL team members Sean Raymond and Rory Barnes in 2005 (shaded region). Observers discovered the planet in the predicted range in the fall of 2007. Right: The orbits of some planets in the Solar System at the same scale. (From AAS press release, also Barnes, Gozdziewski & Raymond 2008, ApJ)

Fig 2. flux.ps — Top: Flux, relative to the present-day Earth, received on a close-in, initially habitable, terrestrial planet on an eccentric orbit experiencing tidal evolution. The solid line represents the orbit-averaged flux, dotted lines represents the flux at periastron and apoastron. The dashed vertical line represents the time that the planet left the habitable zone due to tidal migration. Bottom: Spin frequency of the planet relative to its orbital frequency. Eccentric planets do not rotate synchronously. After 6 Gyr, the orbit is circularized. (From Barnes et al. 2008, Astrobiology)