GEOLOGIC FEATURES ON TITAN'S SURFACE AS REVEALED BY THE CASSINI RADAR

The Cassini Titan Radar Mapper is one of the prime investigations to explore Titan's surface from orbit. Titan has shown itself to be an intriguing object for study, with a variety of unusual candidate materials (e.g., water-ammonia and other ices, hydrocarbons, tholins). Because of its almost opaque atmosphere, microwave remote sensing contributes uniquely to that investigation. The Titan Radar Mapper operates as a passive radiometer, scatterometer, altimeter, and synthetic aperture radar (SAR). In this paper we will review the results obtained so far, which include three fly-bys during which the SAR mode was used (October 2004, February 2005 and September 2005). SAR images revealed that Titan is very geologically complex (see Elachi et al., 2005, Science 13, 970-4). A variety of landforms were imaged, including a large impact (440 km diameter) basin, a smaller (80 km diameter) crater with an ejecta blanket, and a set of radar-bright braided and sinuous channels, apparently draining into a plain. Dark lineated streaks, nicknamed “cat scratches” appear to be surficial and are thought to have been formed by aeolian transport and accumulation. A few radar-dark patches detected during the first fly-by may be candidates for surface liquids. A variety of features thought to be cryovolcanic in origin were seen, including a circular feature thought to be a volcanic dome and extensive flows. The presence of cryovolcanic features on Titan has long been suggested. Its interior may still contain a substantial layer of water-ammonia liquid that may erupt on the surface (e.g. Tobie et al. 2005, Icarus 175, 496-502) and cryovolcanism has been suggested as a way of replenishing methane to the atmosphere. Titan's substantial atmosphere will affect the style of volcanism on Titan, with effusive eruptions being more likely than explosive (Lorenz 1996, Planet. Space Sci. 44, no.9). The findings by the Cassini RADAR's first SAR swath indicate that effusive cryovolcanic features may be common on the surface. Cryovolcanism may be an important resurfacing mechanism on Titan. Based on the small number of impact craters detected, the ~3% of Titan's surface imaged by radar in October 2004 and February 2005 is very young compared with those from other Saturnian satellites.