Scientists have created organic macromolecules by zapping a Titan-like atmosphere with UV rays. The discovery supports the idea that the moon of Saturn could support life.
Earth and Titan are the only known planetary-sized bodies with thick, predominantly nitrogen atmospheres, said Hiroshi Imanaka of the University of Arizona's chemistry and biochemistry department.
"Titan is so interesting because its nitrogen-dominated atmosphere and organic chemistry might give us a clue to the origin of life on our Earth," said Imanaka. "Nitrogen is an essential element of life."
Imanaka and Mark Smith created a nitrogen-methane gas mixture similar to Titan's atmosphere and irradiated it with high-energy UV rays. The Cassini Mission has indicated that 'extreme UV' radiation hitting the atmosphere created complex organic molecules.
Most of the nitrogen moved directly into solid compounds, rather than gaseous ones, said Mark Smith, a UA professor and head of chemistry and biochemistry. Previous models predicted the nitrogen would move from gaseous compounds to solid ones in a lengthier series of steps.
Titan looks orange because a smog of organic molecules envelops the planet. The particles in the smog will eventually settle down to the surface and may be exposed to conditions that could create life, said Imanaka.
However, scientists don't know whether this smog contains nitrogen. If some of the particles are the same nitrogen-containing organic molecules the UA team created in the laboratory, conditions conducive to life are more likely, Smith said.
Imanaka and Smith used the Advanced Light Source at Lawrence Berkeley National Laboratory's synchroton to shoot high-energy UV light into a stainless steel cylinder containing nitrogen-and-methane gas held at very low pressure.
They used a mass spectrometer to analyze the chemicals that resulted. The gases from the cylinder didn't contain any nitrogen-containing organic compounds.
But when they collected the brown gunk that gathered on the cylinder wall and analyzed it, Imanaka said, "Then I finally found the nitrogen!"
Imanaka and Smith suspect that such compounds are formed in Titan's upper atmosphere and eventually fall to the surface. There, they contribute to an environment that is conducive to the evolution of life.