Titan, Saturn’s largest moon, is the best place in the solar system to study
primordial soup — the stuff from which life emerged.

In January 2005, planetary scientists will get a closer look at Titan’s
version of primordial soup when the European Space Agency’s Huygens probe
floats to the surface. The probe currently is riding aboard NASA’s Cassini
spacecraft, which will reach Saturn next July.

“Cassini/Huygens will tell us all about the organics in the atmosphere, the
stuff that’s photochemically processed by sunlight and falls to the
surface,” said University of Arizona planetary sciences Professor Jonathan
I. Lunine. “But what it won’t be quite so good at is telling us what goes on
at the surface.”

Lunine is one of the three interdisciplinary scientists on the
Cassini/Huygens mission, and heads NASA’s Astrobiology Institute focus group
on Titan. This group includes scientists who want to learn more about the
organic chemistry of Titan’s environments.

In addition, Lunine and Mark Smith collaborate with Caltech and NASA Jet
Propulsion Lab colleagues in designing an organic chemistry laboratory that
could be deployed to Titan’s surface. Smith is head of UA’s chemistry

“We really don’t know how life formed on the Earth, or on whatever planet it
formed,” Lunine said. “Because we are organic, with carbon and hydrogen, we
want to know more about organic molecules. How do molecules change
chemically into biomolecules in an environment that is not conducive to
life? There are no traces left of how it happened on Earth because all of
Earth’s organic molecules have been processed biochemically by now. Titan is
our best chance to study organic chemistry in a planetary environment
occurring in the absence of life over billions of years.”

Lunine will talk Friday, Dec. 12, on the astrobiology of Titan at the
American Geophysical Union meeting in San Francisco.

Scientists have focused much of their attention on Titan’s thick atmosphere,
which is four times denser than Earth’s atmosphere at sea level. Like Earth,
and unlike Mars and Venus, Titan has mostly a nitrogen atmosphere. But
because Titan is 10 times farther from the sun than Earth, surface
temperatures hover around minus 290 degrees Fahrenheit. That’s too cold for
water vapor, even though the planet-like moon is half rock and half water.

Titan’s primarily nitrogen atmosphere contains methane. Methane reacts with
ultraviolet sunlight, forming organic compounds that flake from the sky. The
thick atmosphere protects the hydrocarbons and other organic solids that
settle on the surface from being destroyed by damaging particle and
ultraviolet radiation. Some of these organic molecules are thought to have
been important in Earth’s prebiotic environment.

“Cassini-Hugygens will be the stepping stone that will tell us where the
organics are located on the surface, and it will tell us whether there are
differences in organics that have been deposited in craters or in regions
that seem to have been resurfaced by cyrovolcanism.” Cryovolcanism is
volcanism where the fluid is not molten rock, but liquid water that possibly
includes ammonia and other antifreezes. “These are interesting places
because liquid water might have been briefly present and modified the
organics in some way.”

Last year, Lunine and Natalia Artemieva of the Institute for Geospheres in
Moscow published a paper on how much water ice in Titan would melt if the
moon were hit by an asteroid or other object, and how that would affect
organic materials on Titan’s surface.

If astrobiologists don’t get some answers from Titan, they’ll have to hunt
for them in other solar systems.

“Our solar system can be a frustrating place,” Lunine said. “There are only
nine planets – some people say eight because they exclude Pluto – and there
are only 60 moons, not 6,000. And of those 60 moons and 8 or 9 planets,
there’s only one place without life that has abundant organic chemistry,
energy sources, a solid surface where organic molecules can actually survive
and be processed, sometimes along with liquid water. And that place is

Related Web sites