2010 Annual Science Report

NASA Ames Research Center Reporting  |  SEP 2009 – AUG 2010

Disks and the Origins of Planetary Systems

Project Summary

This task is concerned with understanding the evolution of complexity as primitive planetary bodies form in habitable zones. The planet formation process begins with fragmentation of large molecular clouds into flattened protoplanetary disks. This disk is in many ways an astrochemical “primeval soup” in which cosmically abundant elements are assembled into increasingly complex hydrocarbons and mixed in the dust and gas envelope within the disk. Gravitational attraction among the myriad small bodies leads to planet formation. If the newly formed planet is a suitable distance from its star to support liquid water at the surface, it is in the so-called “habitable zone.” The formation process and identification of such life-supporting bodies is the goal of this project.

4 Institutions
3 Teams
12 Publications
0 Field Sites
Field Sites

Project Progress

Co-Is Gorti and Hollenbach continue their theoretical modeling of protoplanetary disks. Gorti gave an oral presentation on their work on time-dependent evolution of viscous disks subject to photoevaporation by Ultraviolet and X-ray photons from the central star at the Circumstellar Disks meeting at ESO, Garching, Germany in November 2009. The main results of that work were that typical disk lifetimes of disk are ~4-5 million years, that disks disperse by first forming gaps at a few AU and then are eroded outwards, and that disk lifetimes are roughly independent of stellar mass and other properties for low-mass stars with M<3 solar masses. Higher mass stars have highly mass-dependent disk lifetimes, with more massive disks destroying their disks very rapidly. Gorti and Hollenbach are also modeling the observed gas line emission from disks and their models of the star TW Hya, suggest that the disk harbors a Jovian mass planet and is being destroyed by photoevaporation. Gorti presented these results at a recent Herschel meeting on star and planet formation at Goteburg, Sweden. This work will be submitted to the Astrophysical Journal shortly. Gorti and Hollenbach will continue modeling other interesting circumstellar disks and apply their theoretical models to infer disk masses. They are also working on models which combine dust evolution, viscous evolution and photoevaporation simultaneously in collaboration with C.P.Dullemond (MPIA, Heidelberg).

Co-I J. Lissauer at the invitation of C. Pilcher (NASA Astrobiology Institute) delivered three 90 minute graduate student level lectures and presented them at the 2010 Santander Summer School: Extrasolar Planets and Habitability, cosponsored by the NAI: http://astrobiology.nasa.gov/nai/UIMP/2010 . As requested by the school, he spent the entire week in Santander to participate in the discussion and be available to interact with the students.

Co-Is S. Davis and D. Richard continue work on models of large scale transport in protoplanetary disks Davis has published a paper on the LCROSS impact event (Davis 2009). Richard is developing models of optical scattering by dust grains that will be published this year (Richard et al, 2010). This work will further our understanding of scattering from small dust particles in both the nebula and in tenuous atmospheres such as the Moon and larger asteroids. S. Davis and D. Richard reported work on the transport properties of chemically induced oxygen isotope distributions in disks at an NAI workshop and at the annual NAI Astrobiology Science Meeting (Davis et al 2010a and 2010b). In this manner we can study the migration of these species into the planet-building zones and ultimately into the meteoritic record where these interesting istotopic anomalies are recorded. Davis has written a paper, now in review, on the location of water ice in the protoplanetary nebula and its ramifications for habitability of extra solar planets (Davis 2010).

Co-I Laughlin continued to lead the development of the publicly available Systemic Console software for the analysis of radial velocity and photometric data sets for extrasolar planets. Specific progress for the year included the implementation of routines for rapidly integrating the long-term evolution of model planetary systems, as well as routines for solving the transit timing inverse problem. The Console software was used to detect and analyze a number of planetary systems, including 61 Vir b,c, and d – a newly discovered planetary system orbiting a nearby solar-type star that contains three Super-Earth category planets. Laughlin published two peer-reviewed articles during the reporting period that describe this work.

    Sanford Davis
    Uma Gorti

    David Hollenbach

    Gregory Laughlin

    Jack Lissauer

    Denis Richard

    Kevin Zahnle

    Objective 1.1
    Formation and evolution of habitable planets.

    Objective 1.2
    Indirect and direct astronomical observations of extrasolar habitable planets.

    Objective 2.1
    Mars exploration.

    Objective 4.3
    Effects of extraterrestrial events upon the biosphere