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Cassini Sees Dramatic Seasonal Changes on Titan
Jet Propulsion Laboratory
October 20, 2016

[Image]
Dusk in the South Slipping into shadow, the south polar vortex at Saturn's moon Titan still stands out against the orange and blue haze layers that
are characteristic of Titan's atmosphere. Image Credit: NASA/JPL-Caltech/Space Science Institute

As southern winter solstice approaches in the Saturn system, NASA's Cassini spacecraft has been revealing dramatic seasonal changes in the atmospheric temperature and composition of Saturn's largest moon, Titan.

Winter is taking a grip on Titan's southern hemisphere, and a strong,
whirling atmospheric circulation pattern -- a vortex -- has developed
in the upper atmosphere over the south pole. Cassini has observed that
this vortex is enriched in trace gases -- gases that are otherwise quite
rare in Titan's atmosphere. Cassini's observations show a reversal in
the atmosphere above Titan's poles since the spacecraft arrived at Saturn
in 2004, when similar features were seen in the northern hemisphere.

"Cassini's long mission and frequent visits to Titan have allowed us to observe the pattern of seasonal changes on Titan, in exquisite detail,
for the first time," said Athena Coustenis, a member of Cassini's Composite Infrared Spectrometer team at the Observatoire de Paris. Coustenis is presenting the team's findings at the joint 48th meeting of the American Astronomical Society Division for Planetary Sciences and 11th European Planetary Science Congress (EPSC), this week in Pasadena, California.
"We arrived at the northern mid-winter and have now had the opportunity
to monitor Titan's atmospheric response through two full seasons."

Heat is circulated through Titan's atmosphere via a pole-to-pole cycle
of warm gases upwelling at the summer pole and cold gases subsiding at
the winter pole. Cassini's observations have shown a large-scale reversal
of this system, beginning immediately after the equinox in 2009.

Titan's hemispheres have responded in different ways to these seasonal changes. The wintry effects have led to a temperature drop of 72 degrees Farenheit (40 degrees Celsius) in the southern polar stratosphere over
the last four years. This contrasts with a much more gradual warming in
the northern hemisphere, where temperatures remained stable during the
early spring and have shown just a six-degree increase since 2014.

Within months following the equinox, the vortex in the stratosphere over
the south pole had become prominent, as had an atmospheric "hot spot"
at high altitudes. The corresponding features in the northern hemisphere
had almost disappeared by 2011.

Inside the polar vortex over the increasingly shadowed south pole, there
has been a rapid build-up of trace gases that accumulate in the absence
of ultraviolet sunlight. These include complex hydrocarbons previously
only seen at high northern latitudes.

A more detailed version of this story is available from the EPSC meeting website:

http://www.europlanet-eu.org/titan-experiences-dramatic-seasonal-changes

News Media Contact
Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-7013
preston.dyches@jpl.nasa.gov

Anita Heward
EPSC Press Office
+44 (0)77 5603 4243
anita.heward@europlanet-eu.org

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