July 2007
The search for life elsewhere in the
solar system and beyond should include research to detect what some
scientists call "weird" life, with biochemistry different from that of
life on Earth, says a new report from the National Research Council.
The assumption that alien life would have the same biochemical
architecture as life on Earth means that scientists have artificially
limited the scope of their thinking as to where extraterrestrial life
might be found, according to the NASA sponsored report.
"Our investigation made clear that life is possible in forms different
than those on Earth," said the chair of the authoring committee John
Baross, professor of oceanography at the University of Washington,
Seattle.
The authors found that the fundamental requirements for life as we know it
- a liquid water biosolvent, carbon-based metabolism, molecular system
capable of evolution, and the ability to exchange energy with the
environment - are not the only ways to support phenomena recognized as
life.
The report emphasizes that "no discovery that we can make in our
exploration of the solar system would have greater impact on our view of
our position in the cosmos, or be more inspiring, than the discovery of an
alien life form, even a primitive one.
At the same time, the report says, "it is clear that nothing would be more
tragic in the American exploration of space than to encounter alien life
without recognizing it."
"It is critical to know what to look for in the search for life in the
solar system," said Baross. "The search so far has focused on Earth-like
life because that's all we know, but life that may have originated
elsewhere could be unrecognizable compared with life here."
"Advances throughout the last decade in biology and biochemistry show that
the basic requirements for life might not be as concrete as we thought,"
he said.
The report stresses that the future search for alien life should not
exclude more research into terrestrial life.
Studies of extreme environments, such as deserts and ocean depths, have
determined that life exists anywhere water and a source of energy are
found together on Earth.
Baross specializes in the ecology, physiology, and taxonomy of
microorganisms from hydrothermal vent environments, and the use of
biochemical and molecular methods to detect, quantify, and classify them.
He is part of NASA's astrobiology team, investigating the origin,
evolution, distribution and future of life on Earth and beyond.
Baross also researches the ecology of extreme environments and the
significance of submarine hydrothermal vent environments for the origin
and evolution of life.
A hydrothermal vent is a fissure in a planet's surface that emits heated
water. Hydrothermal vents are commonly found near volcanically active
places, tectonic plates that are moving apart, ocean basins, and hotspots.
The most famous hydrothermal vent system is probably Yellowstone National
Park in the United States.
Active hydrothermal vents are believed to exist on Jupiter's moon Europa,
and scientists speculate that ancient hydrothermal vents exist on Mars.
The recent evidence that liquid water-ammonia mixtures may exist in the
interior of Saturn's moon Titan suggests the value of another mission to
probe Titan, a place the committee considers the solar system's most
likely home for weird life.
On Wednesday, NASA announced that for the first time the Cassini
spacecraft found cup-like craters filled with hydrocarbons on Saturn's
moon Hyperion, the eighth largest of Saturn's nearly 60 known moons.
NASA scientists said this may indicate the widespread presence in our
solar system of basic chemicals necessary for life.
A paper in the July 5 issue of the journal "Nature" reports details of
Hyperion's surface craters and composition observed during this flyby in
2005, including keys to understanding the moon's origin and evolution over
4.5 billion years.
"Of special interest is the presence on Hyperion of hydrocarbons -
combinations of carbon and hydrogen atoms that are found in comets,
meteorites, and the dust in our galaxy," said Dale Cruikshank, a planetary
scientist at NASA's Ames Research Center, Moffett Field, California, and
the paper's lead author.
"These molecules, when embedded in ice and exposed to ultraviolet light,
form new molecules of biological significance. This doesn't mean that we
have found life," Cruikshank said, "but it is a further indication that
the basic chemistry needed for life is widespread in the universe."
Recent evidence indicates that another moon of Saturn, Enceladus, has
active water geysers, raising the prospect that habitable environments may
exist there.
The report advises that space missions should increase the breadth of
their search for life looking for life forms with DNA structures different
from those on Earth, and life based on different solvents, such as
ammonia, instead of water.
This improved understanding will help scientists to broaden their
perspective, seeking life anywhere the conditions necessary for its
existence might be met.
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