See Beautiful Ontario Lacus: Cassini's Guided Tour

Feature July 15, 2010


See Beautiful Ontario Lacus: Cassini's Guided Tour

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-237&cid=release_2010-237

Ontario Lacus, the largest lake in the southern hemisphere of Saturn's moon Titan, turns
out to be a perfect exotic vacation spot, provided you can handle the frosty, subzero
temperatures and enjoy soaking in liquid hydrocarbon.

Several recent papers by scientists working with NASA's Cassini spacecraft describe
evidence of beaches for sunbathing in Titan's low light, sheltered bays for mooring boats,
and pretty deltas for wading out in the shallows. They also describe seasonal changes in
the lake's size and depth, giving vacationers an opportunity to visit over and over without
seeing the same lake twice. (Travel agents, of course, will have to help you figure out how
to breathe in an atmosphere devoid of oxygen.)

Using data that give us the most detailed picture yet of a lake on another world, scientists
and animators have collaborated on a new video tour of Ontario Lacus (http://www.jpl.nasa.gov/video/index.cfm?id=912.)
based on radar data from Cassini's Titan flybys on June 22, 2009, July 8, 2009, and Jan. 12, 2010.
A Web video explaining how scientists look to Earth's Death Valley are to understand places like
Titan's Ontario Lacus is available at: http://www.jpl.nasa.gov/video/index.cfm?id=913

"With such frigid temperatures and meager sunlight, you wouldn't think Titan has a lot in
common with our own Earth," said Steve Wall, deputy team lead for the Cassini radar
team, based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "But Titan
continues to surprise us with activity and seasonal processes that look marvelously, eerily
familiar."

Cassini arrived at Saturn in 2004 when the southern hemisphere of the planet and its
moons were experiencing summer. The seasons have started to change toward autumn,
with winter solstice darkening the southern hemisphere of Titan in 2017. A year on Titan
is the equivalent of about 29 Earth years.

Titan is the only other world in our solar system known to have standing bodies of liquid
on its surface. Because surface temperatures at the poles average a chilly 90 Kelvin (about
minus 300 degrees Fahrenheit), the liquid is a combination of methane, ethane and
propane, rather than water. Ontario Lacus has a surface area of about 15,000 square
kilometers (6,000 square miles), slightly smaller than its terrestrial namesake Lake Ontario.

Cassini first obtained an image of Ontario Lacus with its imaging camera in 2004. A
paper submitted to the journal Icarus by Alex Hayes, a Cassini radar team associate at the
California Institute of Technology in Pasadena, and colleagues finds that the lake's
shoreline has receded by about 10 kilometers (6 miles). This has resulted in a liquid level
reduction of about 1 meter (3 feet) per year over a four–year period.

The shoreline appears to be receding because of liquid methane evaporating from the lake,
with a total amount of evaporation that would significantly exceed the yearly methane
gas output of all the cows on Earth, Hayes said. Some of the liquid could also seep into
porous ground material. Hayes said the changes in the lake are likely occurring as part of
Titan's seasonal methane cycle, and would be expected to reverse during southern winter.

This seasonal filling and receding is similar to what occurs at the shallow lakebed known
as Racetrack Playa in Death Valley National Park, Hayes said. In fact, from the air, the
topography and shape of Racetrack Playa and Ontario Lacus are quite similar, although
Ontario Lacus is about 60 times larger.

"We are very excited about these results, because we did not expect Cassini to be able to
detect changes of this magnitude in Titan's lakes," Hayes said. "It is only through the
continued monitoring of seasonal variation during Cassini's extended mission that these
discoveries have been made possible."

Other parts of the Ontario Lacus' shoreline, as described in the paper published in
Geophysical Research Letters in March 2010 by Wall, Hayes and other colleagues, show
flooded valleys and coasts, further proof that the lake level has changed.

The delta revealed by Cassini radar data on the western shore of Ontario Lacus is also the
first well-developed delta observed on Titan, Wall said. He explained that the shape of
the land there shows liquid flowing down from a higher plain switching channels on its
way into the lake, forming at least two lobes.

Examples of this kind of channel switching and wave-modified deltas can be found on
Earth at the southern end of Lake Albert between Uganda and the Democratic Republic
of Congo in Africa, and the remains of an ancient lake known as Megachad in the
African country Chad, Wall said.

The radar data also show a smooth beach on the northwestern shore of Ontario Lacus.
Smooth lines parallel to the current shoreline could be formed by low waves over time,
which were likely driven by winds sweeping in from the west or southwest. The pattern
at Ontario Lacus resembles what might be seen on the southeastern side of Lake
Michigan, where waves sculpt the shoreline in a similar fashion.

"Cassini continues to take our breath away as it fills in the details on the surfaces of these
far-off moons," said Linda Spilker, Cassini project scientist based at JPL. "It's
exhilarating to ride along as it takes us on the ultimate cold-weather adventure."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space
Agency and the Italian Space Agency. JPL manages the Cassini-Huygens mission for
NASA's Science Mission Directorate. The Cassini orbiter was designed, developed and
assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency,
working with team members from the United States and several European countries.

More Cassini information is available, at http://www.nasa.gov/cassini and
http://saturn.jpl.nasa.gov.

#2010-237

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