Cassini Shapes First Global Topographic Map of Titan

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http://www.jpl.nasa.gov/news/news.php?release=2013-161

Cassini Shapes First Global Topographic Map of Titan
Jet Propulsion Laboratory
May 15, 2013

Scientists have created the first global topographic map of Saturn's
moon Titan, giving researchers a valuable tool for learning more about
one of the most Earth-like and interesting worlds in the solar system.
The map was just published as part of a paper in the journal Icarus.

Titan is Saturn's largest moon - at 1,600 miles (2,574 kilometers)
across it's bigger than planet Mercury - and is the second-largest moon
in the solar system. Scientists care about Titan because it's the only
moon in the solar system known to have clouds, surface liquids and a
mysterious, thick atmosphere. The cold atmosphere is mostly nitrogen,
like Earth's, but the organic compound methane on Titan acts the way
water vapor does on Earth, forming clouds and falling as rain and
carving the surface with rivers. Organic chemicals, derived from
methane, are present in Titan's atmosphere, lakes and rivers and may
offer clues about the origins of life.

"Titan has so much interesting activity - like flowing liquids and
moving sand dunes - but to understand these processes it's useful to
know how the terrain slopes," said Ralph Lorenz, a member of the Cassini
radar team based at the Johns Hopkins University Applied Physics
Laboratory, Laurel, Md., who led the map-design team. "It's especially
helpful to those studying hydrology and modeling Titan's climate and
weather, who need to know whether there is high ground or low ground
driving their models."

Titan's thick haze scatters light in ways that make it very hard for
remote cameras to "see" landscape shapes and shadows, the usual approach
to measuring topography on planetary bodies. Virtually all the data we
have on Titan comes from NASA's Saturn-orbiting Cassini spacecraft,
which has flown past the moon nearly 100 times over the past decade. On
many of those flybys, Cassini has used a radar imager, which can peer
through the haze, and the radar data can be used to estimate the surface
height.

"With this new topographic map, one of the most fascinating and dynamic
worlds in our solar system now pops out in 3-D," said Steve Wall, the
deputy team lead of Cassini's radar team, based at NASA's Jet Propulsion
Laboratory in Pasadena, Calif. "On Earth, rivers, volcanoes and even
weather are closely related to heights of surfaces - we're now eager to
see what we can learn from them on Titan."

There are challenges, however. "Cassini isn't orbiting Titan," Lorenz
said. "We have only imaged about half of Titan's surface, and multiple
'looks' or special observations are needed to estimate the surface
heights. If you divided Titan into 1-degree by 1-degree [latitude and
longitude] squares, only 11 percent of those squares have topography
data in them."

Lorenz's team used a mathematical process called splining - effectively
using smooth, curved surfaces to "join" the areas between grids of
existing data. "You can take a spot where there is no data, look how
close it is to the nearest data, and use various approaches of averaging
and estimating to calculate your best guess," he said. "If you pick a
point, and all the nearby points are high altitude, you'd need a special
reason for thinking that point would be lower. We're mathematically
papering over the gaps in our coverage."

The estimations fit with current knowledge of the moon - that its polar
regions are "lower" than areas around the equator, for example - but
connecting those points allows scientists to add new layers to their
studies of Titan's surface, especially those modeling how and where
Titan's rivers flow, and the seasonal distribution of its methane
rainfall. "The movement of sands and the flow of liquids are influenced
by slopes, and mountains can trigger cloud formation and therefore
rainfall. This global product now gives modelers a convenient
description of this key factor in Titan's dynamic climate system,"
Lorenz said.

The most recent data used to compile the map is from 2012; Lorenz says
it could be worth revising when the Cassini mission ends in 2017, when
more data will have accumulated, filling some of the gaps in present
coverage. "We felt we couldn't wait and should release an interim
product," he says. "The community has been hoping to get this for a
while. I think it will stimulate a lot of interesting work."

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and ASI, the Italian Space Agency. JPL, a division
of the California Institute of Technology in Pasadena, manages the
mission for NASA's Science Mission Directorate, Washington. The radar
instrument was built by JPL and the Italian Space Agency, working with
team members from the United States and several European countries.

Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jcc...@jpl.nasa.gov

Michael Buckley 240-228-7536
Johns Hopkins Applied Physics Laboratory, Laurel, Md.
Michael...@jhuapl.edu

2013-161