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2008-10-17 08:58:40
Lee Pullen
Astrobiology Magazine
SPACE.com lee Pullen
astrobiology Magazine
space.com Thu Oct 16, 7:02 am ET
Astrobiologists work at the cutting edge of scientific research, investigating
the possibility of life elsewhere in our universe. They are, however, plagued
by a single, potentially critical problem: a lack of samples. Studying alien
organisms is naturally difficult when none have been discovered.
Some scientists have taken a novel approach to circumventing this issue. Life
on Earth is abundant, and often very hardy. Extremophile creatures exist in
places we would consider as exceptionally hostile, such as deep in the ocean
floor or areas where even a drop of water is almost impossible to find.
Similarly, some of the potential places for life elsewhere in our solar system,
such as the planet Mars, Jupiter's moon Europa, or Saturn's moon Titan, have
conditions that are viewed as extremely hostile but still potentially
survivable. So extremophile organisms are studied in lieu of genuine
extraterrestrial samples, to see if they could survive the rigors of life
beyond the Earth.
Nearly indestructible
Dr. Daiki Horikawa from NASA Ames Research Center has been examining strange
creatures called tardigrades for the last seven years. He explains,
"tardigrades are small invertebrate animals, 0.004 to 0.04 inches (0.1 to 1.0
mm) in body length, that live in terrestrial mosses, soil, or lichens. They
also inhabit ocean and polar regions." Often known by their nickname, "water
bears," studies of these bizarre creatures have surprised scientists.
Recent research has shown that water bears can survive the dangerous conditions
of space. Previously, the only organisms that have been exposed to the
radiation and vacuum of space and lived to tell the tale are certain types of
bacteria and lichen. That simple animals like tardigrades also can survive
gives more credence to the theory of panspermia, which claims that organisms
could move from world to world after travelling though space.
Perhaps the most interesting feature of tardigrades is their ability to enter a
suspended animation-like state when they cannot find enough water. In this kind
of survival mode they become very resistant to harsh environments. When they
encounter water they awaken and become active again.
Horikawa realised that if he wanted to produce worthwhile, reproducible
studies, he would have to raise samples of water bears in laboratory
conditions. Those collected from their natural habitat can be quite different
to one another because of climate variations, nutritional differences and other
environmental considerations. So Horikawa raised a collection on agar plates
with green algae for food. Although labor-intensive, this produced uniform
water bears which were then separated into groups and exposed to various
stresses to see how tough they really are.
A barrage of tests
First they were heated up to sizzling temperatures of 194 F (90 C). Then a
group was frozen at -321 F (-196 C). The next batch was given a dose of
radiation similar to what they would receive in space around 4,000 times
stronger than that which would make humans ill. The last selection was covered
in a dissolving chemical (99.8% acetonitrile, a chemical which may be present
in Titan's atmosphere).
The results, published in a recent issue of the journal Astrobiology, were that
water bears in their suspended animation state survived everything that was
thrown at them. Active creatures were less fortunate, but some did tolerate the
extreme conditions. Now their tolerances to specific stresses are known, plans
are underway to expose them to many harsh environments simultaneously.
If extraterrestrial life is as tough and resilient as water bears, then other
worlds could be inhabited. "It's a possibility that water bear-like creatures
could survive and thrive on other planets despite harsh environments," says
Horiwaka. "Judging from data of the planets in our solar system, there could
even be some in their suspended state on Mars." There is a chance that
Earth-based water bears could be transported to other worlds via meteorite
impacts, but more research is required before this is known for sure.
Self-repairing DNA
Horikawa plans on continuing his research, particularly looking at the ability
of water bears to repair DNA after being exposed to high levels of radiation.
As he says, "the most fascinating feature of tardigrades for me is their
ability to survive complete dehydration of the body and high tolerance to
radiation exposure which must cause critical DNA damages."
Horikawa's method of rearing water bears in the laboratory could lead to many
more studies of these amazing animals, and may help astrobiologists in their
search for genuine extraterrestrial life.
Knowing the survival tricks of water bears also could one day be a key
component in enabling the human exploration of the universe.