My work at LPI centers on elucidating the geology and topography of the surfaces of the satellites of the outer planets and Vesta. Of high interest is the unexpectedly rugged topographic relief on Europa and the shapes of impact craters on Europa, Enceladus, and the icy satellites in general. The goal is to understand the geophysical properties of and geologic processes occurring within Europa's floating ice shell and the deformation and mantling of Enceladus surface by plumes, among other things. Topographic mapping of Io is focused on determining volcanic slopes and mountain topography in order to constrain flow rheologies and mountain formation processes on this intensely volcanic world. My work often requires high quality topographic maps, but these must be derived from Voyager, Galileo, and Cassini images using stereo (3-D) image mapping and two-dimensional photoclinometry (shape-from-shading) methods developed here at the Institute. Using these methods, I have been able to map more than 25% of the surfaces of the Galilean satellites of Jupiter and Uranus, as well as nearly all of the surfaces of the icy Saturnian satellites. Mapping of impact crater and basin morphologies on Vesta adds a new dimension to these studies.
I am currently (as of 2012) a Participating Scientist on the Dawn (at Vesta) and Cassini Projects.
One of the many surprises of Saturn's icy moon Iapetus is the prominent topographic ridge that straddles the equator like a walnut. The Cassini orbiter acquired a strip of color and stereo images along this ridge in September 2007, near the boundary between the dark and bright hemispheres. The origin of the ridge is unknown but Cassini's stereo data indicate the ridge at this site is broken into several sharp peaks 15 to 20 kilometers above the surrounding dark cratered plains. These are among the highest peaks in the Solar System. This perspective view looks southeast toward one of these peaks and is based on stereo topography derived from Cassini orbiter imaging data. Patches of bright pure water ice can be seen flanking these dark peaks, which have the brightness of soot. The scene is about 70 kilometers across and is excerpted from a movie showing a hypothetical flight over Iapetus.
The 140-km wide Herschel impact basin dominates Saturn's innermost regular icy satellite. The basin has a a deep bowl-shaped profile with a 5 kilometer high central peak complex. The floor is relatively free of craters and may have formed within the past 2 billion years. Video produced from Cassini imaging data by Paul Schenk, Lunar and Planetary Institute, Houston.