- 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.
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- But it's not too cold for life to exist there, two scientists
say.
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- 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.
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- 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.
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- 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.
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- "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:
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- * 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.
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- * 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.
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- * 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.
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- * 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.
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- http://members.aol.com/mlucen/050120_titan.htm
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