Using adaptive optics on the Gemini North and Keck II
telescopes on Mauna Kea, Hawai’i, a U.S. team has
discovered a new phenomenon in the atmosphere of
Saturn’s largest moon Titan.

Unlike previous observations showing storms at the south
pole, these new images reveal atmospheric disturbances at
Titan’s temperate mid latitudes-about halfway between
the equator and the poles. Explaining the unexpected
activity has proven difficult, and the team speculates that
the storms could be driven by anything from short-term
surface events to shifts in global wind patterns.

“We were fortunate to catch these new mid-latitude clouds
when they first appeared in late 2004,” said team leader
Henry Roe (California Institute of Technology). “We are
not yet certain how their formation is triggered. Continued
observations over the next few years will show us whether
these clouds are the result of a seasonal change in weather
patterns or a surface-related phenomenon.”

The causes of these storms might include activities that
disturb the atmosphere from the surface. It’s possible that
geysers of methane “slush” are brewing from below, or a
warm spot on Titan’s surface is heating the atmosphere.
Cryovolcanism-volcanic activity that spews an icy mix of
chemicals-has also been suggested as one mechanism that
would cause disturbances. It’s also possible that the storms
are driven by seasonal shifts in the global winds that
circulate in the upper atmosphere. Hints about what is
happening on this frigid world could be obtained as the
Huygens probe from the Cassini mission drops through
Titan’s atmosphere in mid-January, 2005.

The Gemini-Keck II observations were the result of good
timing and telescope availability. According to Gemini
scientist Chad Trujillo, Titan’s weather patterns can be
stable for many months, with only occasional bursts of
unusual activity like these recently discovered atmospheric
features. The chances of catching such occurrences depend
largely on the availability of flexible scheduling like that
used at Gemini. “This flexible scheduling is absolutely
critical to Titan meteorology studies,” he said. “Imagine
how hard it would be to understand the Earth’s diverse
meteorological phenomena if you only saw a weather
report a few nights every year.”

Like Earth, Titan is surrounded by a thick atmosphere of
mostly nitrogen. Conditions on Earth allow water to exist in
liquid, solid, or vapor states, depending on localized
temperatures and pressures. The phase changes of water
between these states are an important factor in the
formation of weather in our atmosphere. Titan’s atmosphere
is so cold that any water is frozen solid, but conditions are
such that methane can move between liquid, solid, and
gaseous states. This leads to a methane meteorological
cycle on Titan in analogy to the water-based weather cycle
on Earth.

As it does on Earth, seasonal solar heating can drive
atmospheric activity on Titan, and this could be the
mechanism behind the previously observed south polar
clouds. However, the new temperate-latitude cloud
formations cannot be explained by the same solar heating
process If a seasonal circulation shift is causing the newly
discovered features, the team theorizes that they will drift
northward over the next few years as Titan’s year
progresses through the southern summer and into autumn.
If it is being caused by geological changes, such as
methane geysers or a geologic “warm” spot on the surface,
the feature should stay at the observed 40-degree latitude as
the surface activity spurs changes in atmospheric
convection and methane cloud formation. Continued storm
formations will be easily distinguishable in future ground-
based observations using Gemini, Keck and other adaptive-
optics enabled telescopes.

“Using adaptive optics from the Earth allows us to see
things that just a few years ago would have been invisible,”
said Keck Scientist Antonin Bouchez. “These observations
show that ground-based telescopes are a perfect
complement to space missions like Cassini.”

This research is scheduled for publication in the January 1,
2005 issue of the Astrophysical Journal.

Gemini is an international partnership managed by the
Association of Universities for Research in Astronomy
under a cooperative agreement with the National Science

The national research agencies that form the Gemini
Observatory partnership include: the US National Science
Foundation (NSF), the UK Particle Physics and Astronomy
Research Council (PPARC), the Canadian National
Research Council (NRC), the Chilean Comisisn Nacional
de Investigacisn Cientifica y Tecnolsgica (CONICYT), the
Australian Research Council (ARC), the Argentinean
Consejo Nacional de Investigaciones Cientmficas y Ticnicas
(CONICET) and the Brazilian Conselho Nacional de
Desenvolvimento Cientmfico e Tecnolsgico (CNPq). The
Observatory is managed by AURA under a cooperative
agreement with the NSF.

The W.M. Keck Observatory is operated by the California
Association for Research in Astronomy (CARA), a
scientific partnership of the California Institute of
Technology, the University of California, and the National
Aeronautics and Space Administration.