Searching for Clues to the Solar System's Past in Nearby Young Exosystems: Spitzer Evidence for Planet Forming Collisions and Late Heavy Bombardments

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Date/Time:Monday, 25 Aug 2014 from 4:10 pm to 5:00 pm
Location:Physics 0003
Contact:Massimo Marengo
Phone:515-294-5441
Channel:College of Liberal Arts and Sciences
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Dr. Carey M. Lisse Principal Staff Scientist Johns Hopkins University Applied Physics Laboratory

Recent work analyzing exo-systems with very large mid-infrared excesses has produced a number of very interesting results. First found in the 1983 all-sky IRAS survey, exosystems with ages > 10 Myr demonstrating the so-called "Vega phenomenon", thes systems are now understood to be undergoing important changes in order to produce the massive amounts of detected infrared-bright circumstellar dust. Typical processes invoked to explain the source of the circumstellar dust include collisional grinding of asteroids, high velocity impacts onto growing planetisimals, and sublimation of comets. Judging from events known to have happened in our Solar System, such as the formation of the Moon and the recent impacts on Jupiter, these processes are fundamental to the creation and evolution of planets.

I will present our work on two extraordinary nearby star systems, HD172555 and eta Corvi. Spitzer mid-IR spectra of HD172555 (a 12 Myr old A5V star) demonstrate the presence of large amounts of amorphous silica and SiO produced by a recent impact at hypervelocities (> 10 km/sec). The impact has occurred within the last ~1 Myr, and has created at least a Mercury's mass worth of gas and dust. A similar impact is thought to have created the Earth's Moon. Spitzer mid-IR spectra of the warm, ~360K circumstellar dust around the nearby main sequence star eta Corvi (F2V, ~1.4 Gyr) show clear evidence for warm, water- and carbon-rich dust at ~3 AU from the central star, uncoupled and in a separate reservoir from a previously reported extended sub-mm dust ring at ~150 AU. The observed dust has an equivalent total mass of a 140 km radius asteroid, or a "comet" of 260 km radius. We conclude that the parent body or bodies were Kuiper-Belt or Centaur-like bodies, which captured a large amount of early primitive stellar nebula material and kept it in deep freeze for ~1 Gyr, and were then prompted by dynamical stirring of the system's Kuiper Belt during a Late Heavy Bombardment phase into interacting with a second body at ~3 AU at moderate velocities (5-10 km/sec). A similar event scarred the Earth's moon and may have brought the water and organic material to the Earth necessary to start life.

The study of these and similar systems offer a unique opportunity to understand the processed leading to the formation of rocky planets in our own Solar System, and the delivery of water and carbon-rich material on terrestrial planets in the inner region of planetary systems.

Carey Lisse is Senior Research Scientist at the John Hopkins University Applied Physic Laboratory. With a background in solid state physics and physical chemistry (A.B from Princeton, M.S from UC Berkeley, M.S. and Ph.D. from University of Maryland) he started his astronomy career as instrument scientist for the COBE mission at the NASA Goddard Spaceflight Center. He went on working at the University of Maryland and the Space Telescope Science Institute, where he helped design the current generation Wide Field 3 Camera for the Hubble Space Telescope and worked on the comet bound NASA Deep Impact mission and the EPOXI follow-on. Since 2004 he is Senior Research Scientist at the John Hopkins Advanced Physics Laboratory. His interests are broad, and include the study of the Solar System, planet formation and evolution, and the search for water and life in the galaxy. Dr. Lisse has received numerous awards for his contribution to numerous NASA missions, and in 2004 has been elected as AAAS fellow. Asteroid 12226 Caseylisse has been named in his honor.