[meteorite-list] Scientists Discover Possible Titan Volcano

[Ron Baalke]

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.		   

News Release: 2005-096				June 8, 2005

Scientists Discover Possible Titan Volcano

A recent flyby of Saturn's hazy moon Titan by the Cassini 
spacecraft has revealed evidence of a possible volcano, 
which could be a source of methane in Titan's atmosphere.   

Images taken in infrared light show a circular feature 
roughly 30 kilometers (19 miles) in diameter that does not 
resemble any features seen on Saturn's other icy moons.  
Scientists interpret the feature as an "ice volcano," a 
dome formed by upwelling icy plumes that release methane 
into Titan's atmosphere.  The findings appear in the June 
9 issue of Nature.

"Before Cassini-Huygens, the most widely accepted explanation 
for the presence of methane in Titan's atmosphere was the 
presence of a methane-rich hydrocarbon ocean," said Dr. 
Christophe Sotin, distinguished visiting scientist at NASA's 
Jet Propulsion Laboratory, Pasadena, Calif.  

"The suite of instruments onboard Cassini and the observations 
at the Huygens landing site reveal that a global ocean is not 
present," said Sotin, a team member of the Cassini visual and 
infrared mapping spectrometer instrument and professor at the 
University de Nantes, France.  

"Interpreting this feature as a cryovolcano provides an 
alternative explanation for the presence of methane in Titan's 
atmosphere. Such an interpretation is supported by models of 
Titan's evolution," Sotin said.

Titan, Saturn's largest moon, is the only known moon to have a 
significant atmosphere, composed primarily of nitrogen, with 2 
to 3 percent methane.  One goal of the Cassini mission is to 
find an explanation for what is replenishing and maintaining 
this atmosphere.  This dense atmosphere makes the surface very 
difficult to study with visible-light cameras, but infrared 
instruments like the visual and infrared mapping spectrometer 
can peer through the haze.  Infrared images provide information 
about both the composition and the shape of the area studied.  

The highest resolution image obtained by the visual and 
infrared mapping spectrometer instrument covers an area 150 
kilometers square (90 miles) that includes a bright circular 
feature about 30 kilometers (19 miles) in diameter, with two 
elongated wings extending westward.  This structure resembles 
volcanoes on Earth and Venus, with overlapping layers of 
material from a series of flows.
  
"We all thought volcanoes had to exist on Titan, and now we've 
found the most convincing evidence to date.  This is exactly 
what we've been looking for," said Dr. Bonnie Buratti, team 
member of the Cassini visual and infrared mapping spectrometer 
at JPL.

In the center of the area, scientists clearly see a dark 
feature that resembles a caldera, a bowl-shaped structure formed 
above chambers of molten material. The material erupting from 
the volcano might be a methane-water ice mixture combined with 
other ices and hydrocarbons. Energy from an internal heat source 
may cause these materials to upwell and vaporize as they reach 
the surface.  Future Titan flybys will help determine whether 
tidal forces can generate enough heat to drive the volcano, or 
whether some other energy source must be present.  Black channels 
seen by the European Space Agency's Huygens probe, which 
piggybacked on Cassini and landed on Titan's surface in January 
2005, could have been formed by erosion from liquid methane rains 
following the eruptions.  

Scientists have considered other explanations.  They say the 
feature cannot be a cloud because it does not appear to move and 
it is the wrong composition.  Another alternative is that an 
accumulation of solid particles was transported by gas or liquid, 
similar to sand dunes on Earth.  But the shape and wind patterns 
don't match those normally seen in sand dunes.

The data for these findings are from Cassini's first targeted 
flyby of Titan on Oct. 26, 2004, at a distance of 1,200 kilometers 
(750 miles) from the moon's surface.  

The visual and infrared mapping spectrometer instrument can detect 
352 wavelengths of light from 0.35 to 5.1 micrometers.  It 
measures the intensities of individual wavelengths and uses the 
data to infer the composition and other properties of the 
object that emitted the light; each chemical has a unique 
spectral signature that can be identified.

Forty-five flybys of Titan are planned during Cassini's four-year 
prime mission.  The next one is Aug. 22, 2005.  Radar data of the 
same sites observed by the visual and infrared mapping spectrometer 
may provide additional information.

For more information about the Cassini-Huygens mission visit 
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini .  The 
visual and infrared mapping spectrometer page is at 
http://wwwvims.lpl.arizona.edu .

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 was 
designed, developed and assembled at JPL. The visual and infrared 
mapping spectrometer team is based at the University of Arizona. 

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