Discovery: Icy Satellites


Two new global maps of the front face of Saturn's ice-rich moon Tethys show color variations across the surface (left side), including a bluish band along the equator formed by high-energy electrons, and a new topographic map (where blues are low terrain and reds are high terrain) of the same hemisphere showing the 10-kilometer-deep, 450-kilometer-wide Odysseus impact basin and an irregular 2-kilometer-high topographic ridge forming a circumferential ring around Odysseus.


The extremely young impact crater Inktomi on Saturn's ice-rich moon Rhea splattered bright icy ejecta across a large area. This 40-kilometer-wide crater may have formed in the past 1 million years.


The giant multi-ring Gilgamesh basin is the largest fully preserved impact feature on Ganymede. Unlike Odysseus, this 600-kilometer-wide crater is less than 2 kilometers deep, due to the much higher internal heat flow of Ganymede inducing ice flow in the icy crust.


The ancient dark terrains of Ganymede are geologically complex. This view has been colorized with topographic information where blues are low terrain and reds are high terrain. Originally formed more than 4 billion yearsago, linear fault systems, smooth deposts, and impact craters have completely reshaped the landscape. Many of the craters have also been relaxed and are much shallower than originally formed. Total relief across this 400-kilometer-wide scene is only 2 kilometers.


The highest mountains in the outer solar system, and some of the highest in the entire solar system, are found on rocky volcanic Io, the innermost moon of Jupiter. This view shows the center of Tohil Mons, a 9- kilometer-high massif observed by the Galileo spacecraft. Mountains like these are probably large crustal blocks forced upward by deep compression within the thick volcanic crust. The dark circular areas are active basaltic calderas.

The Voyager, Galileo, and ongoing Cassini missions have been dedicated to mapping these bodies, revealing an amazing diversity of features and important discoveries, including tidal heating, recently formed tectonic fractures, and ongoing ice-rich volcanism. The extensive cratering record can also be used to estimate the ages of these geologic events.


Paul Schenk has been mapping these bodies from spacecraft data, discovering, among other exciting features, plate and crustal rotations on Europa, impact of disrupted comets, the formation of bizarre color deposits on Mimas and Rhea, and diapiric overturn on Triton.


Paul M. Schenk

Planetary Geologist
Paul M. Schenk

My research efforts focus on the geology and topography of the icy satellites of the outer planets and occasionally Mars. Current activities include the study of impact craters and resurfaced regions on icy satellites.