SETI public: Delving Into the Liquid Intrigue of Saturn's Biggest Moon

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Delving Into the Liquid Intrigue of Saturn's Biggest Moon

October 7, 2003
By KENNETH CHANG

Something on Titan, Saturn's largest moon, is very flat,
possibly as flat as the surface of an ocean.

Through an experiment involving radar on an interplanetary
scale, astronomers have made the first observations that
support a long-held suspicion that liquid oceans cover much
of Titan.

With the temperature of Titan estimated at minus 290
degrees Fahrenheit, the liquid cannot be water. Rather,
scientists suspect hydrocarbons, a class of molecules that
consist entirely of hydrogen and carbon. The gas methane is
the lightest hydrocarbon; heavier hydrocarbons are the main
components of smog.

Researchers from Cornell, the University of Virginia and
NASA's Jet Propulsion Laboratory reported their findings in
an article that the journal Science published on its Web
site last week. Titan intrigues planetary scientists. At a
diameter of 3,200 miles, it is larger than Mercury and
Pluto, and its atmosphere, which consists mostly of
nitrogen, is thicker than Earth's.

"It's the largest area of real estate that we don't know
much about in the solar system," said Dr. Donald B.
Campbell, a professor of astronomy at Cornell, who led the
research.

Some astronomers suspect that Titan may even preserve
conditions similar to those that existed on the early
Earth. Although few expect life on Titan, "it could be a
natural laboratory for the chemistry leading to life," said
Dr. Jonathan I. Lunine, a professor at the University of
Arizona's Lunar and Planetary Laboratory.

"Titan is more like a museum," Dr. Lunine said.

Several decades ago, the author and cosmologist Carl Sagan
suggested that methane in Titan's atmosphere could
condense, forming a global ocean.

When NASA's two Voyager spacecraft flew by Saturn in
November 1980 and August 1981, their cameras were unable to
peer through the orange haze of Titan's atmosphere to look
at the surface. Their instruments, however, did not measure
as much methane as would be expected to be evaporating from
an ocean of pure methane.

In 1983, Dr. Lunine and other researchers suggested that
sunlight might generate chemical reactions similar to those
that create smog over cities and that some methane would
turn into heavier hydrocarbons like ethane. "At the time,
we were trying to understand the Voyager data," Dr. Lunine
said.

In 1994, the Hubble Space Telescope took photographs of
Titan in infrared light, which can penetrate the clouds.
They showed splotchy dark and light regions, ruling out a
global ocean. The light areas are probably ice, but the
dark regions may be seas of hydrocarbons.

In November 2001, when Titan came within aim of the Arecibo
radiotelescope in Puerto Rico, the telescope fired the
first in a series of radio pulses. After traveling 750
million miles, the pulse bounced off Titan's surface and
traveled the 750 million miles back to the 1,000-foot-wide
dish in Arecibo, a 2-hour 15-minute round trip. A radio
telescope in West Virginia was also used to detect the
faint echo.

Arecibo fired 25 pulses at Titan. In three-quarters of the
echoes, the astronomers detected sharp reflections like the
blinding glints seen when sunlight bounces off a mirror or
the ocean surface. The most likely explanation is that the
radio waves had bounced off pools of liquid hydrocarbons.

"It's evidence they may be there," Dr. Campbell said. "It's
not conclusive evidence."

The scientists said the data did not tell the size of the
pools, whether they were ponds, lakes or seas.

Dr. Campbell said that it was also possible that the
reflections were produced by smooth solid surfaces, but
that he doubted that much of Titan could be that smooth.

"You would have ice-skating rinks over much of Titan," he
said.

NASA's Cassini spacecraft, which will arrive at Saturn in
July, could provide more definitive answers with radar that
will better map the moon's surface and instruments that can
detect what it is made of.

Cassini is also carrying a probe that will parachute onto
Titan. Instruments on the probe will be able to tell a
splash landing into liquid from a hard crash into ice.

http://www.nytimes.com/2003/10/07/science/space/07TITA.html?ex=1066553844&ei=1&en=0aa74ffce4e3bd66

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