Terrence W. Rettig

Professor,
Astronomy and Astrophysics

Research Interests

How comets are built in young planetary systems is poorly understood. What is the structure of comets and how did they form? Are comets loose "rubble piles" of planetesimals, or are comets uniform chunks of ices like very large "dirty snowballs"? Is the chemistry of comets determined by events in the interstellar medium, or did comets evolve chemically during formation in the disk of the early solar nebula? To answer these questions, Prof. Rettig’s group has used the high resolution imaging capabilities of the Hubble Space Telescope to investigate the structure of the "cores" of the tidally fragmented Comet Shoemaker-Levy 9, and recently, we have been using high-resolution infrared spectra (3-5 microns) from the NASA Infrared Telescope to identify parent volatiles including numerous organic compounds in various comets. Understanding the structure and chemistry of comets will provide a better concept of how comets formed and of the initial accretion conditions that were present in the early solar nebula.

We also use infrared spectra of pre-planetary disks around T Tauri stars to examine the formation processes and abundances of ices in these cold disks such as CO, CO², and H²O. These T Tauri protostars are important because they represent a poorly understood early stage of disk and planetary formation during which the cold shell around a forming star collapses to a preplanetary disk of dirty ices, then comets, and then perhaps planets. Our studies of the abundance of these ices provide information concerning the amount of thermal and chemical processing of icy grains in circumstellar disks that occurs during the early phase of disk evolution and provide clues as to how comets formed during the early history of our solar system. This research also involves a search for evidence of planet formation in disks of more evolved T Tauri stars. As larger protoplanets form in T Tauri disks, they will ‘clean or sweep away’ the nearby dust and ices and produce an annular gap in the disk that might be observable with very high resolution adaptive optics techniques.

Selected Publications:

"The Nature of Comet Shoemaker-Levy 9 Sub-Nuclei from an Analysis of Pre-Impact HST Images," T.W. Rettig, M. J. Mumma, G. J. Sobczak, J. M. Hahn, and M. DiSanti, Journal of Geophysics Research – Planets 101, 9271-9282 (1996).

"Comet Shoemaker-Levy, 9 Dust," J.M. Hahn, T.W. Rettig, and M.J. Mumma, Icarus 121, 291-304 (1994)

"Comet Shoemaker-Levy 9: An Active Comet," T.W. Rettig and J.Hahn, Planetary and Space Science 45, 1271-1277 (1997).

"Carbonyl Sulfide in Comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp): Evidence for an Extended Source in Hale-Bopp," N. Russo, M. DiSanti, M.Mumma, T.W.Rettig, and K. Magee-Sauer, Icarus 135, 377-388 (1998).

"Tidal Disruption of Strengthless Rubble Piles – A Dimensional Analysis," Joseph M. Hahn and Terrence W. Rettig, Planetary and Space Science 46 1677-1682 (1999).

"Identification of Two Sources for Carbon-monoxide in Comet Hale-Bopp," M. DiSanti, M. Mumma, N. Della-Russo, R. Novak, T.W. Rettig, and K. Magee-Sauer, Nature 399,662-665 (1999).

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