This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Through this award, Dr. Pascucci, along with students and collaborators, will complete an on-going ground-based campaign to spectrally resolve bright gas emission lines detected with the Spitzer Space Telescope toward many protoplanetary disks. These observations, combined with the space-based data, will address two fundamental questions related to the formation of giant and terrestrial planets: (1) When and through which mechanisms do gas disks disperse? (2) Can water vapor remain long in the disk to affect the water abundance of terrestrial planets? Specifically, Dr. Pascucci and her collaborators will:
(1) Investigate how to use the emission line from ionized neon at 12.81 microns to trace dissipating gas disks. Disk models predict that this emission is a sensitive tracer of small gas masses in the terrestrial and giant planet forming region of disks. The Spitzer Space Telescope has detected spatially and spectrally unresolved neon emission lines toward many young disks. Dr. Pascucci and her collaborators will use ground-based telescopes to spectrally resolve bright neon lines from 30 prototoplanetary disks. By measuring the widths, peak velocities, and modeling the line profiles, they will separate the emission originating in a disk from that in a jet/outflow and measure the disk radii contributing to the spectal flux, and reveal if X-rays or ultraviolet photons are the major ionization source for neon atoms. This can clarify the role of photoevaporation in dispersing gas disks and guide the use of the numerous spectrally unresolved neon lines in measuring the timescale over which gas disperses.
(2) Map out the distribution and evolution of water in protoplanetary disks. A key yet unanswered question is how Earth acquired its water. A new emerging scenario suggests that this happened relatively early, before Earth was fully formed, by accretion of hydrated silicates migrating inward from the outer asteroid belt. Models of the transport of water in an evolving protoplanetary disk identify robust trends in the evolution of water vapor. Dr. Pascucci and her collaborators will acquire the datasets to test these models. In particular, they will obtain high-resolution L-band spectra of disks in different evolutionary stages that have mid-infrared water lines detected with Spitzer. They will model the line profiles using various codes to: a) estimate the properties of the gas traced by the L-band water lines; and b) investigate if water emission lines are correlated with the disk evolutionary stage as proposed by disk models. Finally, they will work on the combined interpretation of L-band, mid-infrared and far-infrared water lines that they will obtain from their approved Herschel Key program to map out the distribution and evolution of water in protoplanetary disks.
The proposed work is an essential complement to current and upcoming space-based observations, necessary to fully understand the evolution of gas in disks and the implications of this evolution on the formation of giant and terrestrial planets. This research program will form the basis for a PhD thesis for a Johns Hopkins University graduate student and offer small- and large- scale projects for undergraduate students interested in planet formation studies. These activities will train students in using state-of-the-art ground- and space-based facilities and in addressing some of the most fundamental questions in planet formation studies.
