Wednesday, April 27, 2005

Organic soup in Titan's atmosphere

The Cassini probe continues its looping through Saturn's moons. It flew by Titan in its closest approach yet on April 16, coming about 650 miles from the surface of the planet. (A great summary of Cassini's discoveries is here.

A major new result from the recent flyby has been that very complex organics (for example benzene and nitriles) were detected at this height above the surface. In fact, even larger compounds are suspected, but could not be detected, as they fall outside the calibration range of the mass spectrometer. It 's been known that photochemical reactions form these compounds, but at Titan's cold temperatures they should have rained out of the upper atmosphere. (Benzene is also a liquid on Earth.) So something is churning the atmosphere to keep stirring the soup.

The photochemistry of Titan is regarded as an example of potential sources for complex organics necessary for the emergence of life in early Earth. Photochemically generated organics, like those detected in Titan's atmosphere, might also have been generated on the early Earth (and they're still being made in urban smogs), and may have provided the early building blocks for life. Comets contain a similar suite of molecules. However, it's hard to see how cometary organics could make it safely to earth's surface, because the impact energies of big comets (micrometeorites-- space dust-- being an important exception) should incinerate any of these compounds.

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