The Many Moods of Titan

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Jia-Rui Cook 818-354-0850
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Elizabeth Zubritsky 301-614-5438
Goddard Space Flight Center, Greenbelt, Md.
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News feature: 2012-048 Feb. 23, 2012

The Many Moods of Titan

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-048&cid=release_2012-048

A set of recent papers, many of which draw on data from NASA's Cassini spacecraft,
reveal new details in the emerging picture of how Saturn's moon Titan shifts with
the seasons and even throughout the day. The papers, published in the journal
Planetary and Space Science in a special issue titled "Titan through Time", show how
this largest moon of Saturn is a cousin – though a very peculiar cousin – of Earth.

"As a whole, these papers give us some new pieces in the jigsaw puzzle that is
Titan," said Conor Nixon, a Cassini team scientist at the NASA Goddard Space Flight
Center, Greenbelt, Md., who co-edited the special issue with Ralph Lorenz, a Cassini
team scientist based at the Johns Hopkins University Applied Physics Laboratory,
Laurel, Md. "They show us in detail how Titan's atmosphere and surface behave like
Earth's – with clouds, rainfall, river valleys and lakes. They show us that the seasons
change, too, on Titan, although in unexpected ways."

A paper led by Stephane Le Mouelic, a Cassini team associate at the French National
Center for Scientific Research (CNRS) at the University of Nantes, highlights the kind
of seasonal changes that occur at Titan with a set of the best looks yet at the vast
north polar cloud.

A newly published selection of images – made from data collected by Cassini's visual
and infrared mapping spectrometer over five years – shows how the cloud thinned
out and retreated as winter turned to spring in the northern hemisphere.

Cassini first detected the cloud, which scientists think is composed of ethane, shortly
after its arrival in the Saturn system in 2004. The first really good opportunity for
the spectrometer to observe the half-lit north pole occurred on December 2006. At
that time, the cloud appeared to cover the north pole completely down to about 55
degrees north latitude. But in the 2009 images, the cloud cover had so many gaps it
unveiled to Cassini's view the hydrocarbon sea known as Kraken Mare and
surrounding lakes.

"Snapshot by snapshot, these images give Cassini scientists concrete evidence that
Titan's atmosphere changes with the seasons," said Le Mouelic. "We can't wait to see
more of the surface, in particular in the northern land of lakes and seas."

In data gathered by Cassini's composite infrared mapping spectrometer to analyze
temperatures on Titan's surface, not only did scientists see seasonal change on
Titan, but they also saw day-to-night surface temperature changes for the first time.
The paper, led by Valeria Cottini, a Cassini associate based at Goddard, used data
collected at a wavelength that penetrated through Titan's thick haze to see the
moon's surface. Like Earth, the surface temperature of Titan, which is usually in the
chilly mid-90 kelvins (around minus 288 degrees Fahrenheit), was significantly
warmer in the late afternoon than around dawn.

"While the temperature difference – 1.5 kelvins – is smaller than what we're used to
on Earth, the finding still shows that Titan's surface behaves in ways familiar to us
earthlings," Cottini said. "We now see how the long Titan day (about 16 Earth days)
reveals itself through the clouds."

A third paper by Dominic Fortes, an outside researcher based at University College
London, England, addresses the long-standing mystery of the structure of Titan's
interior and its relationship to the strikingly Earth-like range of geologic features
seen on the surface. Fortes constructed an array of models of Titan's interior and
compared these with newly acquired data from Cassini's radio science experiment.

The work shows the moon's interior is partly or possibly even fully differentiated.
This means that the core is denser than outer parts of the moon, although less dense
than expected. This may be because the core still contains a large amount of ice or
because the rocks have reacted with water to form low-density minerals.

Earth and other terrestrial planets are fully differentiated and have a dense iron
core. Fortes' model, however, rules out a metallic core inside Titan and agrees with
Cassini magnetometer data that suggests a relatively cool and wet rocky interior.
The new model also highlights the difficulty in explaining the presence of important
gases in Titan's atmosphere, such as methane and argon-40, since they do not
appear to be able to escape from the core.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space
Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory manages the
mission for NASA's Science Mission Directorate, Washington, D.C. The visual and
infrared mapping spectrometer team is based at the University of Arizona, Tucson.
The composite infrared spectrometer team is based at NASA's Goddard Space Flight
Center in Greenbelt, Md., where the instrument was built. The radio science
subsystem has been jointly developed by NASA and the Italian Space Agency.

-end-

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