10 December 2010

A New View of Tethys

A prime objective of the Cassini orbital mission at Saturn is to characterize the nature and evolution of Saturn's extended family of icy satellites. Cassini observations since the beginning of the prime mission in mid-2004 have made possible the first global maps of these diverse bodies.  A team of scientists lead by Dr. Paul Schenk at the Lunar and Planetary Institute in Houston have produced the first global color and topographic maps of these satellites.  These two views of Tethys show the high-resolution color (at left) and the topography (at right) of the leading, or forward-facing, hemisphere of this 1060-km-diameter ice-rich satellite.  The color map shows the prominent dusky bluish band along the equator, first seen by Voyager in 1980, and shown by the team of scientists lead by Dr. Schenk to be due to the bombardment and alteration of the surface by high energy electrons traveling slower than the satellite's revolution period.  These findings were published in the journal Icarus (see previous posts).  The general reddish tones may be due to the coating of the Tethyean surface by dust-sized particles ejected by Enceladus' south polar plumes.  The view at right is a color-coded topographic map of the same region (blues are low, reds are high).  The total range of topography shown is 10 kilometers from highest to lowest point.  The dominant feature is the 8-kilometer-deep and 440-kilometer-wide Odysseus impact basin at upper left.  Straddling the view like a belt is a previously unknown topographic ridge between 2 and 3 kilometers high.  To the east of the ridge lies ordinary rolling cratered plains, but between the ridge and Odysseus the surface is scoured and pockmarked.  The ridge may be a tectonic feature related to the impact event or may be a deposit formed when the ejecta blasted out of Odysseus slammed back onto the surface at high velocity.  At bottom right can be seen the globe-circling trench Ithaca Chasma, formed as part of Tethys stretched apart.  This map is part of a set of new global topographic maps produced by Dr. Schenk's team for each of Saturn's icy satellites and previewed on-line on this very blog (see previous post)!

Leading Hemisphere of Tethys (base mosaic resolution is 400 meters).
Gloabl color base mosaic (left) and global color-coded topography (right).