Titan: Cold, But Not Too Cold For
Life - Researchers
Special to World Science - 22 January 2005
The Hugyens space probe measured Titan's surface temperature as
minus 180 degrees Celsius - much colder than the lowest ever recorded
on Earth, and almost frigid enough to liquefy oxygen.
But it's not too cold for life to exist there, two scientists say.
Moreover, Titan's peculiar conditions might confer bizarre forms
upon any life existing there, said one of them, Dirk Schulze-Makuch,
associate professor of geology at Washington State University.
Life forms on Titan, he speculated, might have giant cells and lifespans
of thousands of years. "If you have a very cold environment,
everything moves very slowly," he noted. Thus the chemical
processes of life would take longer than on Earth.
Schulze-Makuch, author of a book published last year, "Life
in the Universe," has submitted a paper discussing Titan's
potential for supporting life to the research journal Astrobiology,
along with David Grinspoon of the Southwest Research Institute in
Boulder, Colorado.
"The basic requirements of life, as they are understood today,
are all present on Titan, including organic molecules, energy sources
and liquid media," they wrote. They cited several reasons why
life, at least microbial forms, could exist on Titan, and why if
so it might take forms deeply unfamiliar to us. Some of the considerations
they cited are as follows:
* Cold is bad for life because it slows molecules so they can't
move, keeping them from participating in chemical reactions needed
for life. But some processes on Titan could provide the requisite
heat for reactions, they argue. Ultraviolet rays from the Sun produce
acetylene in Titan's atmosphere, a compound that on Earth is a colorless,
flammable gas. On Titan it is solid and falls down as particles,
transferring solar energy to the ground where it can provide heat
for chemical reactions.
* Many chemicals exist on Titan that cells could use as nutrients.
All it takes is for cells to be able to metabolize them, that is,
orchestrate reactions among them that release energy for the cell
to on live on. Several substances known to exist on Titan can participate
in such reactions, the researchers said, including acetylene and
molecules called radicals, which release huge amounts of energy
upon reacting. On Earth, radicals tend to react so quickly that
their reactions spin out of control and damage rather than help
cells. But Titan's low temperatures would slow the reactions down
to reasonable rates.
* Discoveries with the Huygens probe suggest there may be mud on
Titan, a possibility Schulze-Makuch has proposed before. "It
would be very exciting. There are some hints, some theories, that
life got started with clay minerals or zeolites that are a major
component of mud," he said. Zeolites are crystalline minerals
that serve as good catalysts, substances that speed up chemical
reactions that otherwise would happen to slowly to be useful for
life. Zeolites do this by trapping other molecules together so that
they can react.
* There seems to be no shortage of liquid on Titan, although most
of it appears to be not water but methane, a substance that on Earth
is a colorless, odorless gas, produced when living things decompose
and commonly used as a fuel. Methane may be as capable of supporting
life as water, Schulze-Makuch argues, and could possibly support
bigger cells than exist on Earth. Water molecules have tiny electrical
charges at each end that make them disruptive to some of the chemical
reactions that occur inside cells. Cells in water therefore can
have only a limited surface area exposed to the water, and thus
have a size limit. Most other liquids, such as methane, lack this
charge, eliminating this problem.
http://members.aol.com/mlucen/050120_titan.htm
|
