Saturn’s Titan has been
considered a "unique world in the solar system" since 1908 when, the
Spanish astronomer, José Comas y Solá, discovered that it had an
atmosphere, something non-existent on other moons.
It seems perfectly appropriate that one of the prime candidates for
life in our solar system, Saturn’s largest moon, Titan, should have
surface lakes, lightning, shorelines, relatively thick nitrogen
atmosphere -and seasons. Titan can be viewed as an early-model Earth.
And 100% of all known Earths have awesome life on them. The
significantly lower temperature is a bit of a stumbling block (it’s ten
times as far from the sun as us), but there’s a strong possibility of
subterranean microbial life - or even a prebiotic “Life could happen!”
environment.
If a space traveler ever visits Titan, they will find a world where
temperatures plunge to minus 274 degrees Fahrenheit, methane rains from
the sky and dunes of ice or tar cover the planet’s most arid regions -a
cold mirror image of Earth’s tropical climate, according to scientists
at the University of Chicago.
Titan’s ice is stronger than most bedrock found on earth, yet it is more brittle, causing it to erode more easily, according to new research by San Francisco State University Assistant Professor Leonard Sklar. Sklar and his team developed new measurements from tests on ice as cold as minus 170 degrees Celcius which demonstrate that ice gets stronger as temperature decreases. Understanding ice and its resistance to erosion is critical to answering how Titan’s earth-like landscape formed. Titan has lakes, rivers and dunes, but its bedrock is made of ice as cold as minus 180 degrees Celcius, eroded by rivers of liquid methane.
“You have all these things that
are analogous to Earth. At the same time, it’s foreign and unfamiliar,”
said Ray Pierrehumbert, the Louis Block Professor in Geophysical
Sciences at Chicago.
Titan, one of Saturn’s 60 moons, is the
only moon in the solar system large enough to support an atmosphere.
Pierrehumbert and colleague Jonathan Mitchell, have been comparing
observations of Titan collected by the Cassini space probe and the
Hubble Space Telescope with their own computer simulations of the
moon’s atmosphere.
“One of the things that attracts me about
Titan is that it has a lot of the same circulation features as Earth,
but done with completely different substances that work at different
temperatures,” Pierrehumbert said. On Earth, for example, water forms
liquid and is relatively active as a vapor in the atmosphere. But on
Titan, water is a rock. “It’s not more volatile on Titan than sand is
on Earth.”
Methane-natural gas-assumes an Earth-like role of
water on Titan. It exists in enough abundance to condense into rain and
form puddles on the surface within the range of temperatures that occur
on Titan.
“The ironic thing on Titan is that although it’s much
colder than Earth, it actually acts like a super-hot Earth rather than
a snowball Earth, because at Titan temperatures, methane is more
volatile than water vapor is at Earth temperatures,” Pierrehumbert said.
Pierrehumbert
and Mitchell even go so far as to call Titan’s climate tropical, even
though it sounds odd for a moon that orbits Saturn more than nine times
farther from the sun than Earth. Along with the behavior of methane,
Titan’s slow rotation rate also contributes to its tropical nature.
Earth’s tropical weather systems extend only to plus or minus 30
degrees of latitude from the equator. But on Titan, which rotates only
once every 16 days, “the tropical weather system extends to the entire
planet,” Pierrehumbert said.
Titan’s dense, nitrogen-methane atmosphere responds much more slowly
than Earth’s atmosphere, as it receives about 100 times less sunlight than Earth. Seasons on Titan last more
than seven Earth years. Its clouds form and move much like those on Earth, but in a much slower, more lingering fashion.
Physicists
from the University of Granada and University of Valencia, analyzing
data sent by the Cassini-Huygens probe from Titan, have "unequivocally"
proved that there is natural electrical activity on Titan. The world
scientist community believes that the probability of organic molecules,
precursors of life, being formed is higher on planets or moons which
have an atmosphere with electrical storms.
Scientists
with NASA’s Cassini mission have monitored Titan’s atmosphere for
three-and-a-half years, between July 2004 and December 2007, and
observed more than 200 clouds. They found that the way these clouds are
distributed around Titan matches scientists’ global circulation models.
The only exception is timing — clouds are still noticeable in the
southern hemisphere while fall is approaching.
“Titan’s clouds
don’t move with the seasons exactly as we expected,” said Sebastien
Rodriguez of the University of Paris Diderot, in collaboration with
Cassini visual and infrared mapping spectrometer team members at the
University of Nantes, France. “We see lots of clouds during the summer
in the southern hemisphere, and this summer weather seems to last into
the early fall. It looks like Indian summer on Earth, even if the
mechanisms are radically different on Titan from those on Earth. Titan
may then experience a warmer and wetter early autumn than forecasted by
the models.”
On Earth, abnormally warm, dry weather periods in
late autumn occur when low-pressure systems are blocked in the winter
hemisphere. By contrast, scientists think the sluggishness of
temperature changes at the surface and low atmosphere on Titan may be
responsible for its unexpected warm and wet, hence cloudy, late summer.
Scientists will continue to observe the long-term changes during Cassini’s extended mission, which runs until the fall of 2010,
which will offer plenty of opportunities to monitor climate change on
Titan — the spacecraft makes its next flyby of the moon on June 6.
We’ll learn if the sluggish weather is the result of a slow rate of
temperature change at the surface.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.
Titan’s South Polar Cloud Burst The infrared image of Saturn’s moon
Titan shows a large burst of clouds in the moon’s south polar region.
Image credit: NASA/JPL/University of Arizona/University of Nantes
Posted by Casey Kazan.
Image Top: Titan’s vast dune fields may act like weather vanes to determine general wind direction, have been mapped by scientists who compiled four years of radar data collected by the Cassini spacecraft.
Adapted from materials provided by the University of Chicago and the following sources:
http://www1.nasa.gov/mission_pages/cassini/media/cassini-20090603.html
Adapted from materials provided by Plataforma SINC, via AlphaGalileo.
http://www.sciencedaily.com/releases/2008/07/080729075117.htm
http://www.scientificblogging.com/news_releases/confirmed_electrical_activity_on_titan
http://www.centauri-dreams.org/?p=8105
New infrared images showing the global cloud pattern are available at: http://saturn.jpl.nasa.gov and
http://www.nasa.gov/cassini .
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