The world’s astrobiology community is all abuzz over one of NASA’s most exciting Discovery Mission proposals ever considered to explore the vast methane lakes in the Northern Polar region of Saturn’s moon, Titan. This Titan ocean “Lake Lander” will be an Apollo-mission-like bell-shaped capsule that would be dropped directly into one of the Titan target lakes with a mast to hold a camera. The lake-born probe would use a nuclear-powered engine to run experiments and return data to Earth. When interviewed recently on National Public Radio (listen to the audio below).
.Saturn’s orange moon Titan has hundreds of times more liquid
hydrocarbons than all the known oil and natural gas reserves on Earth,
according to data from NASA’s Cassini spacecraft. The hydrocarbons
rain from the sky, collecting in vast deposits that form lakes and
dunes. Titan is a big laboratory where several of the world’s leading
space scientists get to play with atmospheres on a planetary scale.
At an eye popping minus 179 degrees Celsius (minus 290 degrees
Fahrenheit), Titan has a surface of liquid hydrocarbons in the form of
methane and ethane with tholins believed to make up its dunes. The term
“tholins,” coined by Carl Sagan in 1979, describe the complex organic
molecules at the heart of prebiotic chemistry.
Before
the first Cassini Mission flyby’s Robert Brown who led Cassini’s visual
and infrared mapping spectrometer (VIMS) team, said: “We know VIMS will
see through the haze to Titan’s surface. At closest approach - 1,200
kilometers (745 miles) - we’ll have 600-meter-pixel resolution. We’ll
be able to see very small geologic features. We’ll get very high
resolution looks at atmospheric phenomena, too. But from my
perspective, the really important thing about this encounter is really
digging down below the atmosphere and getting our first real glimpse of
Titan geology.
“We
don’t know what we’re going to encounter there. I suppose you can
assume we’ll see common geologic forms like mountains and craters and
tectonic faults, maybe even volcanism.” Brown was spot on with his
predictions.
VIMS will see Titan’s hydrocarbon pools, if they
exist and aren’t hidden by some low-lying fog or other strange
phenomenon, Brown said
Cassini’s Ion and Neutral Mass
Spectrometer (INMS) took a taste of the mysterious, subtle flavors in Titan’s
atmosphere, team member and UA planetary sciences Professor Roger Yelle
said, scooping up a breath of Titan’s puffy atmosphere during the
flyby, The experiment measured how many molecules of different masses
it got in the gulp of Titan’s mostly nitrogen, methane-laced
atmosphere. Yelle and other Cassini scientists want to identify the
big, complicated hydrogen-and-carbon-containing molecules because they
are part of a planetary system that possibly rains methane and produces
ethane ponds.
Learning more about how carbon-containing, or
“organic,” molecules form doesn’t explain how DNA came to be, Yelle
said. “A single strand of DNA contains about 3 billion nucleotides that
if stretched out, would be something like 1.7 meters long. We’re trying
to understand molecules with just 10 or 12 atoms.”
But Titan’s
hydrocarbon chemistry holds clues that explain the very first steps of
how nature assembled organic molecules, which are the precursors to
amino acids, the building blocks of life, he said.
Cassini to date has mapped about 20 percent of Titan’s surface with radar.
Several hundred lakes and seas have been observed, with each of several
dozen estimated to contain more hydrocarbon liquid than Earth’s oil and
gas reserves. Dark dunes that run along the equator contain a volume of
organics several hundred times larger than Earth’s coal reserves.
Proven reserves of natural gas on Earth total 130 billion tons, enough
to provide 300 times the amount of energy the entire United States uses
annually for residential heating, cooling and lighting. Dozens of
Titan’s lakes individually have the equivalent of at least this much
energy in the form of methane and ethane.
“This global estimate is based mostly on views of the lakes in the
northern polar regions. We have assumed the south might be similar, but
we really don’t yet know how much liquid is there,” said Lorenz.
Cassini’s radar has observed the south polar region only once, and only
two small lakes were visible. Future observations of that area are
planned during Cassini’s proposed extended mission.
“We also know that some lakes are more than 10 meters or so deep
because they appear literally pitch-black to the radar. If they were
shallow we’d see the bottom, and we don’t,” said Lorenz.
The question of how much liquid is on the surface is an important one
because methane is a strong greenhouse gas on Titan as well as on
Earth, but there is much more of it on Titan. If all the observed
liquid on Titan is methane, it would only last a few million years,
because as methane escapes into Titan’s atmosphere, it breaks down and
escapes into space. If the methane were to run out, Titan could become
much colder. Scientists believe that methane might be supplied to the
atmosphere by venting from the interior in cryovolcanic eruptions. If
so, the amount of methane, and the temperature on Titan, may have
fluctuated dramatically in Titan’s past.
A giant, glassy lake larger than Earth’s Lake Ontario occupies Titan’s
south pole according to research from the University of Arizona’s Lunar
and
Planetary Laboratory. The lake which covers 20,000 square
kilometers is filled mostly with methane and ethane, hydrocarbons that
are gases on Earth but liquid on the bone-freezing surface of Titan
-the only solar system moon known to support a planet-like atmosphere.
“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.”
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.
Titan
is
also more squashed in its overall shape—like a rubber ball pressed
down by a foot—than researchers had expected, said Howard Zebker, a
Stanford geophysicist and electrical engineer involved in the work. The
findings may help explain the presence of the large lakes of
hydrocarbons at both of Titan’s poles, which have been puzzling
researchers since being discovered in 2007.
“Since the poles are
squished in with respect to the equator, if there is a hydrocarbon
‘water table’ that is more or less spherical in shape, then the poles
would be closer down to that water table and depressions at the poles
would fill up with liquid,” Zebker said. The shape of the water table
would be controlled by the gravitational field of Titan, which is still
not fully understood.
The
next Cassini fly on August 25, 2009 in the spacecraft's first close
flyby of a moon since Saturn’s August 11 equinox. Highlights this time
include a RADAR ’scrub’ to get more detailed views of the Shangri-La
dunes, unique southern equatorial magnetosphere measurements, and an
opportunity for high-resolution Visible and Infrared Mapping
Spectrometer (VIMS) observations of the southern hemisphere.
Posted by Casey Kazan.
Source Link:
http://uanews.org/node/20615
Posted by Casey Kazan. Adapted from a Jet Propulsion Laboratory release.
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