Jun 10 2010
From The Space Library
RELEASE: 10-335
CASSINI SPOTS POTENTIAL ICE VOLCANO ON SATURN MOON
WASHINGTON -- NASA's Cassini spacecraft has found possible ice volcanoes on Saturn's moon Titan that are similar in shape to those on Earth that spew molten rock. Topography and surface composition data have enabled scientists to make the best case yet in the outer solar system for an Earth-like volcano landform that erupts in ice. The results were presented today at the American Geophysical Union meeting in San Francisco. "When we look at our new 3-D map of Sotra Facula on Titan, we are struck by its resemblance to volcanoes like Mt. Etna in Italy, Laki in Iceland and even some small volcanic cones and flows near my hometown of Flagstaff, said Randolph Kirk, who led the 3-D mapping work, and is a Cassini radar team member and geophysicist at the U.S. Geological Survey (USGS) Astrogeology Science Center in Flagstaff, Ariz. Scientists have been debating for years whether ice volcanoes, also called cryovolcanoes, exist on ice-rich moons, and if they do, what their characteristics are. The working definition assumes some kind of subterranean geological activity warms the cold environment enough to melt part of the satellite's interior and sends slushy ice or other materials through an opening in the surface. Volcanoes on Jupiter's moon Io and Earth spew silicate lava. Some cryovolcanoes bear little resemblance to terrestrial volcanoes, such as the tiger stripes at Saturn's moon Enceladus, where long fissures spray jets of water and icy particles that leave little trace on the surface. At other sites, eruption of denser materials might build up volcanic peaks or finger-like flows. But when such flows were spotted on Titan in the past, theories explained them as non-volcanic processes, such as rivers depositing sediment. At Sotra, however, cryovolcanism is the best explanation for two peaks more than 3000 feet high with deep volcanic craters and finger-like flows. "This is the very best evidence, by far, for volcanic topography anywhere documented on an icy satellite, said Jeffrey Kargel, a planetary scientist at the University of Arizona, Tucson. It's possible the mountains are tectonic in origin, but the interpretation of cryovolcano is a much simpler, more consistent explanation. Kirk and colleagues analyzed new Cassini radar images. His USGS group created the topographic map and 3-D flyover images of Sotra Facula. Data from Cassini's visual and infrared mapping spectrometer revealed the lobed flows had a composition different from the surrounding surface. Scientists have no evidence of current activity at Sotra, but they plan to monitor the area. "Cryovolcanoes help explain the geological forces sculpting some of these exotic places in our solar system, said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. At Titan, for instance, they explain how methane can be continually replenished in the atmosphere when the sun is constantly breaking that molecule down. Cassini launched Oct. 15, 1997, and began orbiting Saturn in 2004. Saturn has more than 60 known moons, with Titan being the largest. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency (ASI). JPL manages the mission for NASA's Science Mission Directorate at the agency's Headquarters in Washington. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and ASI, working with team members from the U.S. and several European countries. The visual and infrared mapping spectrometer was built by JPL, with a major contribution by ASI. The visual and infrared mapping spectrometer science team is based at the University of Arizona, Tucson.
-end-
RELEASE: 10-085
FLASH: NASA'S CASSINI SPACECRAFT SEES LIGHTNING ON SATURN
WASHINGTON -- NASA's Cassini spacecraft has captured images of lightning on Saturn. The images have allowed scientists to create the first movie showing lightning flashing on another planet. After waiting years for Saturn to dim enough for the spacecraft's cameras to detect bursts of light, scientists were able to create the movie, complete with a soundtrack that features the crackle of radio waves emitted when lightning bolts struck. "This is the first time we have the visible lightning flash together with the radio data, said Georg Fischer, a radio and plasma wave science team associate based at the Space Research Institute in Graz, Austria. Now that the radio and visible light data line up, we know for sure we are seeing powerful lightning storms. The movie and radio data suggest extremely powerful storms with lightning that flashes as brightly as the brightest super-bolts on Earth, according to Andrew Ingersoll, a Cassini imaging science subsystem team member at the California Institute of Technology in Pasadena. What's interesting is that the storms are as powerful -- or even more powerful -- at Saturn as on Earth, said Ingersoll. But they occur much less frequently, with usually only one happening on the planet at any given time, though it can last for months. The first images of the lightning were captured in August 2009, during a storm that churned from January to October 2009 and lasted longer than any other observed lightning storm in the solar system. Results are described in an article accepted for publication in the journal Geophysical Research Letters. To make a video, scientists needed more pictures with brighter lightning and strong radio signals. Data were collected during a shorter subsequent storm, which occurred from November through mid-December 2009. The frames in the video were obtained over 16 minutes on Nov. 30, 2009. The flashes lasted less than one second. The images show a cloud as long as 1,900 miles across and regions illuminated by lightning flashes about 190 miles in diameter. Scientists use the width of the flashes to gauge the depth of the lightning below the cloud tops. When lightning strikes on Earth and on Saturn, it emits radio waves at a frequency that can cause static on an AM radio. The sounds in the video approximate that static sound, based on Saturn electrostatic discharge signals detected by Cassini's radio and plasma wave science instrument. Cassini, launched in 1997, and NASA's Voyager mission, launched in 1977, previously had captured radio emissions from storms on Saturn. A belt around the planet where Cassini has detected radio emissions and bright, convective clouds earned the nickname storm alley. Cassini's cameras, however, had been unable to get pictures of lightning flashing. Since Cassini's arrival at Saturn in 2004, it has been difficult to see the lightning because the planet is very bright and reflective. Sunlight shining off Saturn's enormous rings made even the night side of Saturn brighter than a full-moon night on Earth. Equinox, the period around August 2009 when the sun shone directly over the planet's equator, finally brought the needed darkness. During equinox, the sun lit the rings edge-on only and left the bulk of the rings in shadow. Seeing lightning was another highlight of the equinox period, which already enabled scientists to see clumps in the rings as high as the Rocky Mountains. "The visible-light images tell us a lot about the lightning, said Ulyana Dyudina, a Cassini imaging team associate based at Caltech, who was the first to see the flashes. Now we can begin to measure how powerful these storms are, where they form in the cloud layer and how the optical intensity relates to the total energy of the thunderstorms. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory in Pasadena manages the mission for NASA's Science Mission Directorate in Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.
-end-
'
'
'
'
'
'
'
'
