UA: Zapping Titan-Like Atmosphere with UV

[bystander]

Zapping Titan-Like Atmosphere with UV Creates Life Precursors
University of Arizona | College of Science | 29 June 2010

The nitrogen-dominated atmosphere of Saturn's moon, Titan, may provide clues to the origins of life.

The first experimental evidence showing how atmospheric nitrogen can be incorporated into organic macromolecules is being reported by a University of Arizona team. The finding indicates what organic molecules might be found on Titan, the moon of Saturn that scientists think is a model for the chemistry of pre-life Earth.

Earth and Titan are the only known planetary-sized bodies that have thick, predominantly nitrogen atmospheres, said Hiroshi Imanaka ... How complex organic molecules become nitrogenated in settings like early Earth or Titan's atmosphere is a big mystery, Imanaka said.
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Imanaka and Mark Smith converted a nitrogen-methane gas mixture similar to Titan's atmosphere into a collection of nitrogen-containing organic molecules by irradiating the gas with high-energy UV rays. The laboratory set-up was designed to mimic how solar radiation affects Titan's atmosphere.
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Imanaka and Smith suspect that such compounds are formed in Titan's upper atmosphere and eventually fall to Titan's surface. Once on the surface, they contribute to an environment that is conducive to the evolution of life.

How did life begin on Earth?
Scientific American | Observations | 29 June 2010

[bystander]

Modeling the atmosphere of Titan at the Advanced Light Source
Lawrence Berkeley National Laboratories | 01 July 2010

Most life can’t use stable nitrogen molecules unless they’re fixed in reactive compounds, so nitrogenated organic compounds are essential constituents of life on Earth and probably any other planet with life. While almost 80 percent of Earth’s atmosphere is nitrogen gas, only small amounts of fixed nitrogen are found there; most nitrogen compounds are currently made by life itself. How did the cycle begin?

Hiroshi Imanaka, a chemist and planetologist at the University of Arizona (UA) and, not incidentally, a member of the SETI Institute (SETI stands for Search for Extraterrestrial Intelligence), thinks the clues may lie in the atmosphere of Saturn’s largest moon, Titan. Titan has the only substantial atmosphere in our solar system besides Earth’s that’s mostly nitrogen.
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Short of hitching a ride on a passing spaceship, how does one study the atmosphere of Titan? The answer is to use synchrotron light from Berkeley Lab’s Advanced Light Source (ALS), optimized to produce bright beams of just the kind of extreme ultraviolet (EUV) and vacuum ultraviolet (VUV) light thought to energize Titan’s nitrogen chemistry.

At the ALS Chemical Dynamics Beamline 9.0.2, Imanaka and his UA colleague Mark Smith irradiated a mixture of nitrogen gas and methane in a 95-to-five-percent ratio, seeking to create highly reactive compounds capable of kick-starting the formation of nitrogenated organic aerosols in Titan’s atmosphere.

Ultraviolet experiments with carbon-nitrogen compounds found in Earth’s stratosphere have been conducted in the past, but the nitrogen-methane mix used by Imanaka and Smith was never tested this way. The researchers sent the mixture flowing through the synchrotron’s beam inside a vacuum chamber.

In initial runs, Imanaka and Smith used a mass spectrometer to analyze only the altered gases. They found mixtures of hydrocarbons like benzene in amounts consistent with what is actually observed in Titan’s atmosphere, but they saw no evidence of complex nitrogen compounds.

Formation of nitrogenated organic aerosols in the Titan upper atmosphere

• Proceedings of the National Academy of Sciences, 28 June 2010, pdf

[bystander]

Study shows how sunlight on Titan yields life-precursor compounds
Scientific American | Observations | 03 July 2010

Titan, Saturn's largest moon, does not harbor alien life as far as anyone knows, but the prospects for extraterrestrial biology there are about as good there as anywhere else in the solar system.

Numerous promising compounds based on hydrogen, nitrogen and carbon—some of the key constituents of terrestrial biological molecules such as amino acids—have been detected in Titan's atmosphere. Now a new study shows how readily Titan's thick atmosphere produces those chemicals, which might precipitate down to the moon's surface.

Hiroshi Imanaka of the University of Arizona and the SETI Institute in Mountain View, Calif., and Mark A. Smith of the University of Arizona report the results of their laboratory re-creation of Titan's atmospheric chemistry in a study published online this week in Proceedings of the National Academy of Sciences.

The researchers filled a chamber at Lawrence Berkeley National Laboratory's Advanced Light Source with a simulated Titan atmosphere—mostly nitrogen with a dash of methane—and bombarded the mixture with ultraviolet radiation. What they found was that a substantial quantity of nitrogen gas (N2) in the atmosphere is split by photodissociation, then incorporated into reactive compounds such as HCCN and finally into stable organic macromolecules.

"Organic aerosols in the upper atmosphere of Titan might be a hidden [nitrogen] sink," the researchers report, "which eventually accumulate on the surface of Titan with chemical potential for prebiotic evolution."

Of course, it is a long way from nitrogenated organic compounds hundreds of kilometers above Titan to any kind of life down in the methane lakes on the moon's surface. But as with a recent pair of much-publicized studies showing chemical processes consistent with but not indicative of life on Titan, it's at least a step in the right direction.

http://asterisk.apod.com/vie ... 31&t=19672