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Life on Earth may have roots in air: early atmosphere capable of assembling life's ingredients.

When it comes to determining exactly where in the solar system life began, things have never been so up in the air. Over the past decade, scientists have suggested deep-sea hydrothermal vents (SN: 2/2/08, p. 67), underground aquifers, partially frozen lakes (SN: 10/23/10, p. 11) and even comets as locations for the origin of life.

Now an experiment that simulates chemical reactions in the atmosphere of Titan, Saturn's haze-shrouded moon, adds a new location to the list of unexpected places where the chemistry of life could have developed--in the sky.

Using radio waves as an energy source to bombard a mix of gases in a steel reaction chamber, researchers simulated ultraviolet radiation from the sun striking the top of Titan's thick atmosphere and breaking apart gas molecules such as methane and molecular nitrogen. The experiment is the first to produce, without liquid water, the basic chemical ingredients of life--the amino acids found in proteins and the nucleotide bases that make up DNA and RNA.

The results suggest that Titan's upper atmosphere, about 1,000 kilometers above the frigid moon's surface, could produce chemical precursors to life, planetary scientist Sarah Horst of the University of Arizona in Tucson reported October 7. And because planetary scientists believe that Titan provides a snapshot of the early Earth, the study also indicates that building blocks for terrestrial life might have formed within a primordial haze high above the planet rather than in a primordial soup on the surface, Horst said.

Planetary scientist Jonathan Lunine, also of the University of Arizona but not part of the study, notes that the compounds found in the experiment "are relatively simple precursor molecules to life, and so there are a lot of additional steps between such molecules and life itself, most of which will likely require a liquid, such as water or methane." However, he adds, everything that forms high in Titan's atmosphere does eventually end up in the moon's lakes and seas of methane.

The study is provocative, Lunine says, because the Saturn-orbiting Cassini spacecraft has detected heavy charged molecules in Titan's atmosphere, but they are too massive for the craft's instruments to identify. Researchers have looked at amino acids as some of the potential candidates for these large compounds.

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To confirm that amino acids and nucleotide bases are actually produced in Titan's atmosphere will require another orbiter that can carry instruments 100 to 200 kilometers deeper than Cassini does into Titan's haze layer, Lunine says.

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Title Annotation:Atom & Cosmos
Author:Cowen, Ron
Publication:Science News
Geographic Code:1USA
Date:Nov 6, 2010
Words:415
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