Titan's vast dune fields, which may act like weather
vanes to determine general wind direction
on Saturn's biggest moon, have been mapped by scientists
who compiled four years of radar data
collected by the Cassini spacecraft.
Titan's rippled dunes are generally oriented
east-west. Surprisingly, their orientation and
characteristics indicate that, near the surface, Titan's
winds blow toward the east instead of toward
the west. This means that Titan's surface winds blow
opposite the direction suggested by previous
global circulation models of Titan.
"At Titan there are very few clouds, so determining
which way the wind blows is not an easy
thing, but by tracking the direction in which Titan's sand
dunes form, we get some insight into the
global wind pattern," said Ralph Lorenz, Cassini radar
scientist at the Johns Hopkins University
Applied Physics Laboratory. "Think of the dunes sort of
like a weather vane, pointing us to the
direction the winds are blowing." A paper based on these
findings appeared in the Feb. 11 issue of
Geophysical Research Letters.
Jani Radebaugh, of Brigham Young University, said,
"Titan's dunes are young, dynamic features
that interact with topographic obstacles and give us clues
about the wind regimes. Winds come at
these dunes from at least a couple of different directions
but then combine to create the overall dune
orientation," she said.
The wind pattern is important for planning future
Titan explorations that might involve balloon-
Some 16,000 dune segments were mapped out from about
20 radar images, digitized and
combined to produce the new map.
Titan's dunes are believed to be made up of
hydrocarbon sand grains likely derived from organic
chemicals in Titan's smoggy skies. The dunes wrap around
high terrain, which provides some idea of
their height. They accumulate near the equator and may pile
up there because drier conditions allow
for easy transport of the particles by the wind. Titan's
higher latitudes contain lakes and may be
"wetter" with more liquid hydrocarbons, not ideal
conditions for creating dunes.
The new map, based on all the high-resolution radar
data collected during a four-year period, is
Cassini, which launched in 1997 and is now in extended
mission operations, continues to blaze its
trail around the Saturn system and will visit Titan again
on March 27. Seventeen Titan flybys are
planned this year.
The Cassini-Huygens mission is a cooperative project
of NASA, the European Space Agency and
the Italian Space Agency.