Saturn Moon's Atmosphere May Hold Ingredients for Life

Composite view of Titan built with Cassini images taken on Oct. 9 and Oct. 25, 2006. CREDIT: NASA/JPL/University of Arizona

This story was updated at 8:05 p.m. EDT on Oct. 7.

The hazy atmosphere of Saturn's largest moon, Titan, may contain complex organic molecules that are the building blocks of life as we know it, a new study suggests.

In the lab, researchers simulated possible chemical reactions occurring high up in the nitrogen-rich atmosphere of Titan. They found that various complex molecules, such as amino acids and nucleotide bases, could form without much prodding.

"We can do this entirely in an atmosphere," researcher Sarah Horst, a University of Arizona graduate student, said in a statement. "We don't need liquid water, we don't need a surface. We show that it is possible to make very complex molecules in the outer parts of an atmosphere."

The molecules synthesized in the experiment include the five nucleotide bases found in the genetic code of life on Earth — cytosine, adenine, thymine, guanine and uracil — and the two smallest amino acids, glycine and alanine, researchers said.

Horst presented the results today (Oct. 7) at the 42nd annual meeting of the American Astronomical Society's Division of Planetary Sciences in Pasadena, Calif.

Complex chemistry on Titan

Titan's atmosphere is thick and nitrogen-rich, like Earth's. But Titan is much colder, with average surface temperatures around minus 290 degrees Fahrenheit (minus 179 degrees Celsius) — far too frosty for liquid water to exist. Titan's weather system is based on methane, with methane rain drizzling down and pooling in liquid lakes.

Titan's upper atmosphere has all the elements necessary for complex, interesting, Earth-like chemistry to take place, Horst told reporters today (Oct. 7). Huge molecules of mysterious origin float about up there, some of them containing 1,000 carbon atoms.

The upper atmosphere also contains oxygen — likely contributed by giant ice geysers erupting on Titan's fellow moon, Enceladus — and is bombarded by solar radiation powerful enough to break chemical bonds and spur reactions, Horst said.

Horst and her colleagues wanted to see just what types of molecules such reactions could produce, so the team set up a lab experiment.

Recreating Titan in the lab

The scientists created a cold mixture of nitrogen, methane and carbon monoxide — a rough approximation of Titan's upper atmosphere — in a reaction chamber, then zapped it with radio-frequency radiation strong enough to break tough nitrogen bonds.

The radio-frequency radiation didn't replicate exactly what the sun beams out, but it suited the team's needs, according to Horst.

"The really important thing is that you have enough energy to break that [nitrogen] bond," she said. "We know there's enough energy to break those bonds on Titan."

The experiment produced a slew of complicated molecules; the team has identified some 20,000 different kinds using mass spectrometry, Horst said. Included in this number are amino acids and nucleotide bases — the first time these molecules have been synthesized in an atmosphere simulation experiment without the use of liquid water, researchers said.

The results suggest that Titan's upper atmosphere could be a reservoir of prebiotic molecules that could serve as the springboard to life, according to the scientists.

And the find may offer a new perspective on the emergence of life on Earth as well: Instead of a primordial soup, the first ingredients of life on our planet may have formed from a primordial haze high in Earth's atmosphere.

Moreover, the results show that it may be possible to study these processes in a planetary environment — particularly in the atmosphere of Titan — to gain a deeper understanding of this chemistry, researchers said.

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