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 liquidhydrocarbons than all the known oil and natural gas reserves on Earth,according to data from NASA"s Cassini spacecraft. The hydrocarbonsrain from the sky, collecting in vast deposits that form lakes anddunes. Titan is a big laboratory where several of the world"s leadingspace scientists get to play with atmospheres on a planetary scale.
At an eye popping minus 179 degrees Celsius (minus 290 degreesFahrenheit), Titan has a surface of liquid hydrocarbons in the form ofmethane and ethane with tholins believed to make up its dunes. The term"tholins," coined by Carl Sagan in 1979, describe the complex organicmolecules at the heart of prebiotic chemistry.
Beforethe first Cassini Mission flyby"s Robert Brown who led Cassini"s visualand infrared mapping spectrometer (VIMS) team, said: "We know VIMS willsee through the haze to Titan"s surface. At closest approach - 1,200kilometers (745 miles) - we"ll have 600-meter-pixel resolution. We"llbe able to see very small geologic features. We"ll get very highresolution looks at atmospheric phenomena, too. But from myperspective, the really important thing about this encounter is reallydigging down below the atmosphere and getting our first real glimpse ofTitan geology.
"Wedon"t know what we"re going to encounter there. I suppose you canassume we"ll see common geologic forms like mountains and craters andtectonic faults, maybe even volcanism." Brown was spot on with hispredictions.
VIMS will see Titan"s hydrocarbon pools, if theyexist and aren"t hidden by some low-lying fog or other strangephenomenon, Brown said
Cassini"s Ion and Neutral MassSpectrometer (INMS) took a taste of the mysterious, subtle flavors in Titan"satmosphere, team member and UA planetary sciences Professor Roger Yellesaid, scooping up a breath of Titan"s puffy atmosphere during theflyby, The experiment measured how many molecules of different massesit got in the gulp of Titan"s mostly nitrogen, methane-lacedatmosphere. Yelle and other Cassini scientists want to identify thebig, complicated hydrogen-and-carbon-containing molecules because theyare part of a planetary system that possibly rains methane and producesethane ponds.
Learning more about how carbon-containing, or"organic," molecules form doesn"t explain how DNA came to be, Yellesaid. "A single strand of DNA contains about 3 billion nucleotides thatif stretched out, would be something like 1.7 meters long. We"re tryingto understand molecules with just 10 or 12 atoms."
But Titan"shydrocarbon chemistry holds clues that explain the very first steps ofhow nature assembled organic molecules, which are the precursors toamino 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 severaldozen estimated to contain more hydrocarbon liquid than Earth"s oil andgas reserves. Dark dunes that run along the equator contain a volume oforganics several hundred times larger than Earth"s coal reserves.
Proven reserves of natural gas on Earth total 130 billion tons, enoughto provide 300 times the amount of energy the entire United States usesannually for residential heating, cooling and lighting. Dozens ofTitan"s lakes individually have the equivalent of at least this muchenergy in the form of methane and ethane.
"This global estimate is based mostly on views of the lakes in thenorthern polar regions. We have assumed the south might be similar, butwe really don"t yet know how much liquid is there," said Lorenz.Cassini"s radar has observed the south polar region only once, and onlytwo small lakes were visible. Future observations of that area areplanned during Cassini"s proposed extended mission.
"We also know that some lakes are more than 10 meters or so deepbecause they appear literally pitch-black to the radar. If they wereshallow we"d see the bottom, and we don"t," said Lorenz.
The question of how much liquid is on the surface is an important onebecause methane is a strong greenhouse gas on Titan as well as onEarth, but there is much more of it on Titan. If all the observedliquid on Titan is methane, it would only last a few million years,because as methane escapes into Titan"s atmosphere, it breaks down andescapes into space. If the methane were to run out, Titan could becomemuch colder. Scientists believe that methane might be supplied to theatmosphere by venting from the interior in cryovolcanic eruptions. Ifso, the amount of methane, and the temperature on Titan, may havefluctuated dramatically in Titan"s past.
A giant, glassy lake larger than Earth"s Lake Ontario occupies Titan"ssouth pole according to research from the University of Arizona"s LunarandPlanetary Laboratory. The lake which covers 20,000 squarekilometers is filled mostly with methane and ethane, hydrocarbons thatare 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 at5-micron wavelengths," Brown said. "It was hard for us to accept thefact that the feature was so black when we first saw it. More than 99.9percent of the light that reaches the lake never gets out again. For itto be that dark, the surface has to be extremely quiescent, mirrorsmooth. No naturally produced solid could be that smooth."
Before the Cassini mission, several scientists thought that Titan wouldbe awash in global oceans of ethane and other light hydrocarbons, thebyproducts of photolysis, or the action of ultraviolet light on methaneover 4.5 billion years of solar system history. But 40 close flybys ofTitan by the Cassini spacecraft show no such oceans exist.
Titanisalso more squashed in its overall shapelike a rubber ball presseddown by a footthan researchers had expected, said Howard Zebker, aStanford geophysicist and electrical engineer involved in the work. Thefindings may help explain the presence of the large lakes ofhydrocarbons at both of Titan"s poles, which have been puzzlingresearchers since being discovered in 2007.
"Since the poles aresquished in with respect to the equator, if there is a hydrocarbon"water table" that is more or less spherical in shape, then the poleswould be closer down to that water table and depressions at the poleswould fill up with liquid," Zebker said. The shape of the water tablewould be controlled by the gravitational field of Titan, which is stillnot fully understood.
Thenext Cassini fly on August 25, 2009 in the spacecrafts first closeflyby of a moon since Saturn"s August 11 equinox. Highlights this timeinclude a RADAR "scrub" to get more detailed views of the Shangri-Ladunes, unique southern equatorial magnetosphere measurements, and anopportunity for high-resolution Visible and Infrared MappingSpectrometer (VIMS) observations of the southern hemisphere.
NPR Audio InterviewPosted 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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