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Titan’s
Surface Organics Surpass Oil Reserves On Earth
Wednesday, February 13, 2008
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Pools
on Titan
An
artist's imagination of hydrocarbon pools, icy and rocky
terrain on the surface of Saturn's largest moon Titan.
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Image
Credit: Steven Hobbs (Brisbane, Queensland, Australia).
Video
Credit: NASA / JPL
Saturn’s orange moon
Titan has hundreds of times more liquid hydrocarbons than all the
known oil and natural gas reserves on Earth, according to new
Cassini data. The hydrocarbons rain from the sky, collecting in
vast deposits that form lakes and dunes.
The new
findings from the study led by Ralph Lorenz, Cassini radar team
member from the Johns Hopkins University Applied Physics
Laboratory, USA, are reported in the 29 January 2008 issue of the
Geophysical Research Letters.
"Titan is just covered
in carbon-bearing material—it’s a giant factory of
organic chemicals," said Lorenz. “This vast carbon
inventory is an important window into the geology and climate
history of Titan.”
At a balmy minus 179º C ,
Titan is a far cry from Earth. Instead of water, liquid
hydrocarbons in the form of methane and ethane are present on the
moon's surface, and tholins probably make up its dunes. The term
‘tholins’ was coined by Carl Sagan in 1979 to
describe the complex organic molecules at the heart of prebiotic
chemistry.
Cassini has mapped about 20% of Titan's
surface with radar. Several hundred lakes and seas have been
observed, with each of several dozen estimated to contain more
hydrocarbon liquid than Earth's oil and gas reserves. The dark
dunes that run along the equator contain a volume of organics
several hundred times larger than Earth's coal reserves.
Proven reserves of natural gas
on Earth total 130 thousand million tons, enough to provide 300
times the amount of energy the entire United States uses annually
for residential heating, cooling and lighting. Dozens of Titan's
lakes individually have the equivalent of at least this much
energy in the form of methane and ethane.
"This
global estimate is based mostly on views of the lakes in the
northern polar regions. We have assumed the south might be
similar, but we really don’t yet know how much liquid is
there," said Lorenz. Cassini's radar has observed the south
polar region only once, and only two small lakes were visible.
Future observations of that area are planned during Cassini’s
proposed extended mission.
Scientists estimated Titan's
lake depth by making some general assumptions based on lakes on
Earth. They took the average area and depth of lakes on Earth,
taking into account the nearby surroundings, like mountains. On
Earth, the lake depth is often 10 times less than the height of
nearby terrain.
"We also know that some lakes are
more than 10 m or so deep because they appear literally
pitch-black to the radar. If they were shallow we'd see the
bottom, and we don't," said Lorenz.
The question of how much liquid
is on the surface is an important one because methane is a strong
greenhouse gas on Titan as well as on Earth, but there is much
more of it on Titan. If all the observed liquid on Titan is
methane, it would only last a few million years, because as
methane escapes into Titan's atmosphere, it breaks down and
escapes into space. If the methane were to run out, Titan could
become much colder. Scientists believe that methane might be
supplied to the atmosphere by venting from the interior in
cryovolcanic eruptions. If so, the amount of methane, and the
temperature on Titan, may have fluctuated dramatically in Titan’s
past.
“We are carbon-based life, and understanding
how far along the chain of complexity towards life that chemistry
can go in an environment like Titan will be important in
understanding the origins of life throughout the universe,”
added Lorenz.
Cassini's next radar flyby of Titan is on
22 February 2008, when the radar instrument will observe the
landing site of ESA’s Huygens probe.
Source:
ESA / NASA
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