To help answer the question of whether life has emerged elsewhere
in the solar system than on Earth, astrobiologists look to Mars and
Jupiter's ice-sheathed moon, Europa, as potential incubators.
But for a look at how key chemical ingredients - carbon, seasoned
with hydrogen, nitrogen, and other elements - may have mixed to form
the pre-biotic building blocks necessary for organic life to emerge,
researchers are looking to Saturn's moon, Titan.
Taken together, researchers say, these three - Mars, Europa, and
Titan - may unlock the secrets of the evolution of organic material
in the universe, from simple atoms forged in stars to the rich
complexity of organic life on Earth. Of the three, Titan remains the
most enigmatic, says Jonathan Lunine, a planetary scientist at the
University of Arizona in Tucson and a member of the Cassini-Huygens
mission to study Saturn and its systems of rings and moons.
Researchers will get their first close-up look at the moon and
its chemical stew at the end of 2004, when the Cassini spacecraft
begins the first in a series of 45 close fly-bys of Titan during its
four-year mission. In January 2005, Cassini is slated to drop the
European-built Huygens probe into Titan's atmosphere. If all goes
well, the probe should continue to return data from the moon's
surface for up to half an hour before falling silent.
"We think there are enormous quantities of organics in the
atmosphere and on the surface, and for that reason alone, it's an
interesting astrobiological target," Dr. Lunine says. "It may be an
even more interesting target because there's the possibility that
there have been energy sources and maybe liquid water in times and
places on the surface that would have allowed these organics to
evolve the kind of chemistry that might lead towards life."
Titan's atmosphere is thought to resemble that of Earth a few
hundred million years after it coalesced from the disk of dust and
gas that surrounded the young sun. Studies have shown that Titan's
atmosphere presents a chemical face only an organic chemist could
love, noted Lunine, during a series of briefings here this week
conducted by the Council for the Advancement of Science Writing.
Once thought to be largely methane, Titan's atmosphere is now
known to consist mainly of molecular nitrogen. Through chemical
reactions triggered by sunlight, the nitrogen and methane recombine
to form a range of organic compounds. …