Scientists have found possible ice volcanoes on Saturn's moon Titan, similar to those on Earth that spew molten rock.
Topography and surface composition data from NASA's Cassini Spacecraft have enabled scientists to make the best case yet for an Earth-like volcanic landform that erupts with ice instead of lava.
Titan is the largest moon of Saturn and the only natural satellite known to have a dense atmosphere. Titan is also the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found.
The landform spotted by Cassini is known as Sotra Facula. It bears a strong resemblance to volcanoes on Earth. 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, a geophysicist at the U.S. Geological Survey Astrogeology Science Center in Flagstaff, Arizona.
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.
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Cryovolcanoes form on icy moons, and possibly on other low-temperature astronomical objects. Rather than molten rock, these volcanoes erupt volatiles such as water, ammonia or methane. Collectively referred to as cryomagma or ice-volcanic melt, these substances are usually liquids, but can also be gases. After eruption, cryomagma freezes solid when exposed to the very low surrounding temperature.
The energy required to melt ices and produce cryovolcanoes usually comes from tidal friction. It has also been suggested that translucent deposits of frozen materials could create a sub-surface greenhouse effect that would accumulate the required heat.
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 first explained them as non-volcanic processes, such as rivers depositing sediment.
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.
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.
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.
Launched on Oct. 15, 1997, Cassini began orbiting Saturn in 2004. Saturn has more than 60 known moons, with Titan being the largest.
Frequently described as a planet-like moon, Titan has a diameter roughly 50 percent larger than Earth's moon and is 80 percent more massive. Titan is the second-largest moon in the Solar System, after Jupiter's moon Ganymede, and it is larger by volume than the smallest planet, Mercury, although only half as massive.
Titan, the first known moon of Saturn, was discovered in 1655 by the Dutch astronomer Christiaan Huygens.
The results of the latest findings were presented Wednesday at the American Geophysical Union meeting in San Francisco.