Tethys, Saturn
http://photojournal.jpl.nasa.gov/catalog/PIA08884 PIA08884: Odysseus Out of Shadow Target Name: Tethys Is a satellite of: Saturn Mission: Cassini Spacecraft: Cassini Orbiter Instrument: Imaging Science Subsystem - Narrow Angle Product Size: 254 samples x 255 lines Produced By: Cassini Imaging Team Primary Data Set: Cassini Full-Res TIFF: PIA08884.tif (65.06 kB) Full-Res JPEG: PIA08884.jpg (3.732 kB) Click on the image to download a moderately sized image in JPEG format (possibly reduced in size from original). Original Caption Released with Image: The Cassini spacecraft stares directly into the great Odysseus impact basin on Tethys. Peaks near the crater's center cast long shadows toward the east. The elevated eastern rim of the crater catches sunlight, despite being well beyond the terminator. See PIA07693 for a highly detailed view of Odysseus. Lit terrain seen here is on the anti-Saturn hemisphere of Tethys (1,071 kilometers, or 665 miles across) -- the side that always faces away from Saturn. North is up. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 19, 2007 at a distance of approximately 1.1 million kilometers (700,000 miles) from Tethys. Image scale is 7 kilometers (4 miles) per pixel. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov/home/index.cfm . The Cassini imaging team homepage is at http://ciclops.org . Image Credit: NASA/JPL/Space Science Institute http://photojournal.jpl.nasa.gov/catalog/PIA08913 PIA08913: Odysseus Into the Dark Target Name: Tethys Is a satellite of: Saturn Mission: Cassini Spacecraft: Cassini Orbiter Instrument: Imaging Science Subsystem - Narrow Angle Product Size: 209 samples x 217 lines Produced By: Cassini Imaging Team Primary Data Set: Cassini Full-Res TIFF: PIA08913.tif (45.63 kB) Full-Res JPEG: PIA08913.jpg (2.185 kB) Click on the image to download a moderately sized image in JPEG format (possibly reduced in size from original). Original Caption Released with Image: Odysseus impact basin lies between night and day on Tethys. Lit terrain seen here is on the anti-Saturn side of Tethys (1,071 kilometers, or 665 miles across), or the side that always faces away from Saturn as the moon orbits the planet. North is up. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 26, 2007 at a distance of approximately 1.5 million kilometers (1 million miles) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 96 degrees. Image scale is 9 kilometers (6 miles) per pixel. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov/home/index.cfm . The Cassini imaging team homepage is at http://ciclops.org . Image Credit: NASA/JPL/Space Science Institute MEDIA RELATIONS OFFICE JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIF. 91109 TELEPHONE 818-354-5011 http://www.jpl.nasa.gov Carolina Martinez 818-354-9382 Jet Propulsion Laboratory, Pasadena, Calif. Monica Talevi +31-71-565-3223 European Space Agency, Noordwijk, Netherlands Gill Ormrod +44-1793-442012 Science and Technology Facilities Council, London, England Maria Martinez 210-522-3305 Southwest Research Institute, San Antonio NEWS RELEASE: 2007-065 June 14, 2007 Cassini Finds Saturn Moons Are Active Saturn’s moons Tethys and Dione are flinging great streams of particles into space, according to data from the Cassini mission to Saturn. The discovery suggests the possibility of some sort of geological activity, perhaps even volcanic, on these icy worlds. These results appear in this week's issue of the journal Nature. The Cassini mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The particles were traced to the two moons because of the dramatic outward movement of electrically charged gas, which could be mapped back to the moons' orbits in the magnetic environment of Saturn. Known as plasma, the gas is composed of negatively charged electrons and positively charged ions, which are atoms with one or more electrons missing. Because they're charged, the electrons and ions can become trapped inside a magnetic field. Saturn rotates in just 10 hours and 46 minutes. This sweeps the magnetic field and the trapped plasma through space. Just like a child on a fast-spinning merry-go-round, the trapped gas feels a force trying to throw it outwards, away from the center of rotation. Soon after the Cassini spacecraft reached Saturn in June 2004, its instruments revealed that the planet’s hurried rotation squashes the plasma into a disc, and that great fingers of gas are being thrown out into space from the disc’s outer edges. Hotter, more tenuous plasma then rushes in to fill the gaps. Now, Jim Burch, team member of the Cassini Plasma Spectrometer at the Southwest Research Institute, San Antonio, Texas, and his colleagues have made a careful study of these events using the instrument. They have found that the direction of the ejected electrons points back towards Tethys and Dione. “It establishes Tethys and Dione as important sources of plasma in Saturn’s magnetosphere,” said Burch. Until this discovery, the only moons of Saturn known to be active worlds were Titan and Enceladus. “This new result seems to be a strong indication that there is activity on Tethys and Dione as well,” said Andrew Coates from the Mullard Space Science Laboratory, University College London, co-author and member of the Cassini Plasma Spectrometer team. Activity is a draw for planetary scientists, as it means that the planet has yet to become geologically dead or is perhaps being supplied with energy. The activity on Enceladus was detected first by Cassini's Dual Technique Magnetometer. This led the flight team to schedule a particularly close pass of Enceladus, which revealed a wealth of data about Enceladus’ alien geysers - and spectacular pictures, too. “The best results arise when we combine a variety of data sets to understand the observations,” said Michele Dougherty, Imperial College, London, who is principal investigator of the magnetometer. Future flybys of Dione and Tethys will allow the magnetometer team and the other instrument teams a close-up look at the moons. Before that happens, the teams have to go back and search for further signs of activity in the data already collected during the Tethys and Dione flybys of 2005. In addition, having detected the electrons, they will try to determine the composition of the Tethys and Dione plasma using ion data. More information on the Cassini mission is available at: http://www.nasa.gov/cassini, http://saturn.jpl.nasa.gov and http://saturn.esa.int . The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL. The Cassini Plasma Spectrometer team is based at the Southwest Research Institute in San Antonio. The magnetometer team is based at Imperial College in London, working with team members from the United States and several European countries. -end- http://antwrp.gsfc.nasa.gov/apod/ap070909.html The Great Basin on Saturn's Tethys Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA Explanation: Some moons wouldn't survive the collision. Tethys, one of Saturn's larger moons at about 1000 kilometers in diameter, survived the collision, but sports today the expansive impact crater Odysseus. Sometimes called the Great Basin, Odysseus occurs on the leading hemisphere of Tethys and shows its great age by the relative amount of smaller craters that occur inside its towering walls. Another large crater, Melanthius, is visible near the moon's terminator. The density of Tethys is similar to water-ice. The above digitally enhanced image was captured in July by the robot Cassini spacecraft in orbit around Saturn as it swooped past the giant ice ball. http://antwrp.gsfc.nasa.gov/apod/ap071217.html Saturn's Ancient Rings Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA Explanation: How old are Saturn's rings? No one is quite sure. One possibility is that the rings formed relatively recently in our Solar System's history, perhaps only about 100 million years ago when a moon-sized object broke up near Saturn. Evidence for a young ring age includes a basic stability analysis for rings, and the fact that the rings are so bright and relatively unaffected by numerous small dark meteor impacts. New evidence, however, raises the possibility that some of Saturn's rings may be billions of years old and so almost as old as Saturn itself. Inspection of images by the Saturn-orbiting Cassini spacecraft indicates that some of Saturn's ring particles temporarily bunch and collide, effectively recycling ring particles by bringing fresh bright ices to the surface. Seen here, Saturn's rings were imaged in their true colors by the robotic Cassini in late October. Icy bright Tethys, a moon of Saturn likely brightened by a sandblasting rain of ice from sister moon Enceladus, is visible in front of the darker rings.

<img src="http://apod.nasa.gov/apod/image/0806/tethys3_cassini.jpg" width="800"> http://apod.nasa.gov/apod/ap080624.html Ithaca Chasma: The Great Rift on Saturn's Tethys Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA Explanation: What created the Great Rift on Saturn's moon Tethys? No one is sure. More formally named Ithaca Chasma, the long canyon running across the right of the above image extends about 2,000 kilometers long and spreads as much as 100 kilometers wide. The above image was captured by the Saturn-orbiting robotic Cassini spacecraft as it zoomed by the icy moon last month. Hypotheses for the formation of Ithaca Chasma include cracking of Tethy's outer crust as the moon cooled long ago, and that somehow the rift is related to the huge Great Basin impact crater named Odysseus, visible elsewhere on the unusual moon. Cassini has now been orbiting Saturn for about four years and is scheduled to continue to probe and photograph Saturn for at least two more years.