Caltech Scientists Discover Storms in the Tropics of Titan

Caltech News Release
For immediate release
August 12, 2009


Caltech Scientists Discover Storms in the Tropics of Titan

Pasadena, Calif. - For all its similarities to Earth - clouds that
pour
rain (albeit liquid methane not liquid water) onto the surface
producing lakes and rivers, vast dune fields in desert-like regions,
plus a smoggy orange atmosphere that looks like Los Angeles's during
fire season - Saturn's largest moon, Titan, is generally "a very
bland
place, weatherwise," says Mike Brown of the California Institute of
Technology (Caltech).

"We can watch for years and see almost nothing happen. This is bad
news for people trying to understand Titan's meteorological cycle, as
not only do things happen infrequently, but we tend to miss them when
they DO happen, because nobody wants to waste time on big telescopes
-
which you need to study where the clouds are and what is happening to
them - looking at things that don't happen," explains Brown, the
Richard and Barbara Rosenberg Professor of Planetary Astronomy.

However, just because weather occurs "infrequently" doesn't mean it
never occurs, nor does it mean that astronomers, in the right place
at the right time, can't catch it in the act.

That's just what Emily Schaller - then a graduate student of Brown's
-
and colleagues accomplished when they observed, in April 2008, a
large system of storm clouds appear in the apparently dry mid-
latitudes and then spread in a southeastward direction across the
moon. Eventually, the storm generated a number of bright but
transient clouds over Titan's tropical latitudes, a region where
clouds had never been seen - and, indeed, where it was thought they
were extremely unlikely to form.

Schaller, now a Hubble Postdoctoral Fellow at the University of
Arizona, Brown, and their colleages; Henry Roe, a former Caltech
postdoctoral scholar in Brown's group, now at the Lowell Observatory
in Flagstaff; and Tapio Schneider, a professor of environmental
science and engineering at Caltech, describe their work, and its
implications for climate on Titan, in the August 13 issue of Nature.

"A couple of years ago, we set up a highly efficient system on a
smaller telescope to figure out when to use the biggest telescopes,"
Brown says. The first telescope, NASA's Infrared Telescope Facility,
on Mauna Kea, takes a spectrum of Titan almost every single night.
"=46rom that we can't tell much, but we can say 'no clouds,' 'a few
clouds,' or, if we get lucky 'monster clouds,'" he explains.

Schaller explains, "The period during which I was collecting data for
my thesis, sadly, corresponded entirely to an extended period of
essentially no clouds, so we never really got to show the full power
of the combined telescopes. But then, after finishing and turning in
my thesis, I walked back across campus to my office to look at the
data from the previous night to find that Titan suddenly had the
biggest clouds ever. I like to think it was Titan's graduation gift
to me. Or perhaps a bad joke."

The day after the telescope's big find (and Schaller's thesis
submission), Schaller, Brown, and Roe began tracking the clouds with
the large Gemini telescope on Mauna Kea and watched this system
evolve for a month. "And what a cool show it was," Brown says.

"The first cloud was seen near the tropics and was caused by a still-
mysterious process, but it behaved almost like an explosion in the
atmosphere, setting off waves that traveled around the planet,
triggering their own clouds. Within days a huge cloud system had
covered the south pole, and sporadic clouds were seen all the way up
to the equator."

Schneider, an expert on atmospheric circulations, was instrumental in
helping to sort out the complicated chain of events that followed the
initial outburst of cloud activity.

"The monthlong event has many important implications for
understanding the hydrological cycle on Titan," says Brown, "but one
of the reasons I am most excited about it is that it shows clouds
near the equator - where the [European Space Agency's] Huygens probe
landed - for the first time. For a while now, people have speculated
that the equatorial regions are simply too dry to ever have
significant clouds."

And yet, the images snapped by the Huygens probe in January 2005, as
it descended through Titan's soupy atmosphere and toward the surface,
revealed small-scale channels and streams, which looked just like
features created by fluids - by water, here on Earth, and on Titan,
probably by liquid methane.

Experts had speculated for years on how there could be streams and
channels in a region with no rain. The new results suggest those
speculations may prove unneccessary. "No one considered how storms in
one location can trigger them in many other locations," says Brown.

The paper, "Storms in the tropics of Titan," appears in the August 13
issue of Nature. The research was supported by a Hubble Postdoctoral
Fellowship (to Schaller), the NASA Planetary Astronomy Program, and a
Planetary Astronomy Grant from the National Science Foundation.

For more information about the discovery, go to

http://www.mikebrownsplanets.com .

Images available upon request.


Contact:
Kathy Svitil

626-395-8022