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Project Progress

Module 2: Formation of Habitable Planetary Systems

Meyer and colleagues continue to use data from the Spitzer Space Telescope to study the formation and evolution of planetary systems. Recent highlights include using observations of warm dust to constrain theories of planet formation. Preliminary results suggest that the processes thought to have lead to the formation of terrestrial planets in our solar system could be very common around sun-like stars. Follow-up studies include: a) analysis of the disk chemistry using mid-infrared spectra from Spitzer (led by Ilaria Pascucci); b) deep sub-millimeter surveys for gas and dust (led by Arizona students Stephanie Cortes and Alan Aversa); and c) thermal IR
search for planets thought to be the outcome of such processes (led by Daniel Apai). In collaboration with former student Eric Mamajek, Meyer investigated whether forming planets
could be detected as hot proto-planet collision afterglows. The results could have implications for strategies to obtain the first images or terrestrial planets with ground- or space-based telescopes.

Joan Najita and colleagues continues to develop the tools for studying the gas in the planet formation region of disks. With John Carr, she reported the detection of organic molecules and water in typical T Tauri disks using high resolution Spitzer spectroscopy
in the journal Science. With Al Glassgold and Rowin Meijerink, she has been enhancing disk chemistry models to understand the disk physical and chemical conditions that are needed to
produce such emission. Carr and Najita have also been using high resolution IR spectroscopy of CO fundamental emission to study the gas content and distribution in T Tauri disks. In a recent paper, they report that the CO emission in one transition object is radially truncated and lay out the possible interpretations, including the presence of an orbiting planetary companion. In a complementary approach, Dr. Najita and post-doctoral fellow Greg Doppmann have used IR molecular absorption spectroscopy to probe the properties of organic molecules in the disk atmosphere of an edge on disk. In another line of investigation, Greg Doppmann, Josh Eisner and Najita have used high resolution IR spectroscopy to explore the origin of the hot compact
excess in MWC 480 detect with interferometry. They find no evidence that the emission is due to hot water emission, in contrast with an earlier study, and explore the alternative explanations.

Bond and Lauretta are studying how extrasolar planetary host stars are chemically distinct from the general stellar population, displaying significant variations in key planet-building elements such as Fe, C, O, Mg, and Si. These enrichments are rimordial in origin, established in the giant molecular cloud from which these systems formed. As a result, the chemistry of planet-building materials in many of these systems is distinctly different from that in our Solar System. Using combined chemical and dynamical modeling (in collaboration with D. O’Brien of the Planetary Science Institute) of planet formation in known extrasolar planetary systems, they have found that terrestrial planets are ubiquitous. Furthermore, the mass and chemistry of these planets is highly variable. For example, errestrial planets similar to Earth are believed to exist in the majority of extrasolar planetary systems while on the other hand systems that are enriched in C, regardless of the actual C abundance, produce terrestrial planets that are dominated by carbide phases. In the context of planet formation models within realistic circumstellar disks, they plan to investigate (with M. Meyer) how these compositional variations influencw the interior structure and processes, surface compositions and features, atmospheric chemistry, and the possibility of life.
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