- As NASA prepares to set twin robots loose on the Martian
surface and makes plans to send another in 2007, the agency's long term
goal is clear: Determine whether the red planet does or ever did harbor
life.
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- But the current search for life is necessarily limited
to life as we know it, organisms dependent on liquid water. A SPACE.com
reader recently suggested that "we as humans are arrogant, simply
believing that any other form of life will be just like us."
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- Researchers devoted to the search for ET have a similar
view.
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- "Scientists approach to finding life is very Earth-centric,"
says Kenneth Nealson, a geobiologist at the University of Southern California.
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- The problem is, beyond carbon-based, water-dependent
life, there isn't much intelligence to go on when designing a multi-million
mission to Mars.
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- "Based on what we know about life on Earth, we set
the limits for where we might look on other planets," Nealson said.
Within that framework, however, there are extreme cases of life on Earth
that suggest the range of places to look on frigid Mars.
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- Extreme beings
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- Nealson and his colleagues recently found the most extreme
sort of organism known, in terms of the temperatures it can survive.
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- Corien Bakersman, a postdoctoral student in Nealsons
lab, discovered bacteria named psychrobacter cryopegella. It grows and
reproduces in conditions as chilly as 14 degrees Fahrenheit (-10 degrees
Celsius).
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- The discovery, in a salty liquid lake under the permafrost
of Siberia, was reported in a recent issue of the journal Astrobiology.
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- The bacteria can continue to metabolize even at temperatures
down to -4 degrees Fahrenheit (-20 Celsius), though they understandably
stop reproducing at that extreme.
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- "This organism can exist at colder temperatures
than any previously discovered," Nealson said.
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- Nealson's team figures that at certain times in the history
of Mars, the tilting of its pole to a more oblique angle would have caused
the north polar cap to warm to -4 Fahrenheit or higher as it received more
sunlight.
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- "If the ice at the polar caps warmed to liquid water,
organisms like cryopegella could have awakened and repaired any damage
that might have occurred to their various cellular components," Nealson
said. "Then, as the obliquity changed a few million years later and
the planet got colder and colder, these organisms would have been the last
survivors."
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- That does not mean there are necessarily dormant microbes
within the ice caps of Mars. But it does suggest a broader range of potential
cradles for life, places Nealson figures should be considered.
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- Other researchers agree, and a host of so-called "extremophile"
discoveries on Earth in recent years indicate the polar regions of Mars
might be prime hunting grounds. As on Earth, organisms there might be slathered
in natural antifreeze or be able to go dormant for tens of thousands of
years, waiting for a brief thaw, their moment in the Sun.
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- The two landers en route now will not explore the polar
regions. NASA's Mars Phoenix lander, slated for launch in 2007, is intended
to investigate the north polar area.
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- Life as we don't know it
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- Meanwhile, scientists recognize that there could indeed
be life elsewhere in the universe that does not require water. And some
astrobiologists are trying to explore the possibilities. But it is a tough
problem to approach. In looking for "life as we don't know it,"
it's hard to even imagine what to expect.
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- Nealson is at the forefront of a nascent effort to at
least contemplate what might be out there.
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- "It'll have shape and composition. It'll have structure,"
Nealson said at a gathering of astrobiologists last year. These characteristics
are necessary to convert one type of energy to another, a process he considers
fundamental to life.
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- There are other basics, he says: "Life replicates,
and life evolves. And because it consumes energy, it produces waste products.
And it has some particular activities that seem to be universal, one of
which is movement."
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- Life might or might not exist on Mars. If there are critters
there, they might or might not be like bacteria on Earth. In laboratory
conditions, scientists in 2001 were able to get one-celled organisms to
incorporate an amino acid -- a fundamental building block of life -- that
no other known life uses. The discovery borders on the creation of artificial
life, experts said. It also suggests that ET might operate by entirely
different rules than those we're used to.
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- If life on Mars is fundamentally different from what
scientists understand life to be, then current spacecraft and others in
the works may well not recognize what's right under their mechanical noses.
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- This article is part of SPACE.com's weekly Mystery Monday
series.
- Copyright © 2003 SPACE.com.
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