[meteorite-list] Saturn's Moon Titan Has A Liquid Surface Lake

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 30 Jul 2008 16:23:01 -0500
Message-ID: <013001c8f28a$72a16e90$122ee146_at_ATARIENGINE>

First confirmed existence of a lake of any liquid on the
surface of any planet or body in the solar system -- the
envelope, please! -- goes to Titan. The lake is liquid
ethane.

There are seas, lake, and rivers seen in the region of
the North Pole, and the prevailing suspicion (but no
proof) has been that they are methane, but now ethane
may seem more likely.

This lake is located near the South Pole, is named
Ontario Lactus, or Lake Ontario. It's about the same
size as Earth's Lake Ontario; the existence of a Canada
on its north shore has not been confirmed.

No lakes or seas have been seen outside the polar regions.
Evidence suggests that "rain" falls only at the Poles, where
the lakes are. Oddly, cold as Titan is, it may be that it is
too "hot" for rain and bodies of water except at the Poles
and that the hazy atmosphere is, in effect, cold "steam."

Full text of the press release is below.

Sterling K. Webb
--------------------------------------------------------------------

http://www.sciencedaily.com/releases/2008/07/080730140726.htm

Scientists have confirmed that at least one body in our
solar system, other than Earth, has a surface liquid lake.
Using an instrument on NASA's Cassini orbiter, they
discovered that a lake-like feature in the south polar
region of Saturn's moon, Titan, is truly wet. The lake is
about 235 kilometers, or 150 miles, long.

The visual and infrared mapping spectrometer, or VIMS, an
instrument run from The University Arizona, identifies the
chemical composition of objects by the way matter reflects
light.

When VIMS observed the lake, named Ontario Lacus, it
detected ethane, a simple hydrocarbon that Titan experts
have long been searching for. The ethane is in liquid
solution with methane, nitrogen and other low-molecular
weight hydrocarbons.

"This is the first observation that really pins down that
Titan has a surface lake filled with liquid," VIMS
principal investigator and professor Robert H. Brown of
UA's Lunar and Planetary Laboratory said. Brown and his
team report their results in the July 31 issue of the
journal Nature.

"Detection of liquid ethane in Ontario Lacus confirms a
long-held idea that lakes and seas filled with methane and
ethane exist on Titan," said Larry Soderblom of the U.S.
Geological Survey, Flagstaff, Ariz.

The fact that the VIMS could detect the spectral
signatures of ethane on the moon's dimly lit surface while
viewing at a highly slanted angle through Titan's thick
atmosphere "raises expectations for exciting future lake
discoveries by the infrared spectrometer," Soderblom, an
interdisciplinary Cassini scientist, said.

The ubiquitous hydrocarbon haze in Titan's atmosphere
hinders the view to Titan's surface. But there are
transparent atmospheric "windows" at certain infrared
light wavelengths through which Cassini's VIMS can see to
the ground. VIMS observed Ontario Lacus on Cassini's 38th
close flyby of Titan in December 2007.

The lake is roughly 20,000 square kilometers, or 7,800
square miles, just slightly larger than North America's
Lake Ontario, Brown said. Infrared spectroscopy doesn't
tell the researchers how deep the lake is, other than it
must be at least a centimeter or two, or about
three-quarters of an inch, deep.

"We know the lake is liquid because it reflects
essentially no light at 5-micron wavelengths," Brown said.
"It was hard for us to accept the fact that the feature
was so black when we first saw it. More than 99.9 percent
of the light that reaches the lake never gets out again.
For it to be that dark, the surface has to be extremely
quiescent, mirror smooth. No naturally produced solid
could be that smooth."

VIMS observations at 2-micron wavelengths shows the lake
holds ethane. The scientists saw the specific signature of
ethane as a dip at the precise wavelength that ethane
absorbs infrared light. Tiny ethane particles almost as
fine as cigarette smoke are apparently filtering out of
the atmosphere and into the lake, Brown said.

Ethane is a simple hydrocarbon produced when ultraviolet
light from the sun breaks up its parent molecule, methane,
in Titan's methane-rich, mostly nitrogen atmosphere.

Before the Cassini mission, several scientists thought
that Titan would be awash in global oceans of ethane and
other light hydrocarbons, the byproducts of photolysis, or
the action of ultraviolet light on methane over 4.5
billion years of solar system history. But 40 close flybys
of Titan by the Cassini spacecraft show no such oceans
exist.

The observations also suggest the lake is evaporating. The
lake is ringed by a dark beach, where the black lake
merges with the bright shoreline.

"We can see there's a shelf, a beach, that is being
exposed as the lake evaporates," Brown said.

That the beach is darker than the shoreline could mean
that the "sand" on the beach is wet with organics, or it
could be covered with a thin layer of liquid organics, he
said.

The VIMS measurements rule out the presence of water ice,
ammonia, ammonia hydrate and carbon dioxide in Ontario
Lacus.

The VIMS result gives researchers new insight on Titan's
chemistry and weather dynamics.

Titan, which is one-and-a-half times the size of Earth's
moon and bigger than either Mercury or Pluto, is one of
the most fascinating bodies in the solar system when it
comes to exploring environments that may give rise to
life.

Cassini cameras and radar and the UA-built camera aboard
the European Space Agency's Huygens probe that landed on
Titan in January 2005 have shown that methane saturates
and drains from Titan's atmosphere, creating river-like
and lake-like features on the surface. Just as water
cycles through the hydrologic regime on Earth, methane
cycles through a methanological cycle on Titan.
Received on Wed 30 Jul 2008 05:23:01 PM PDT