Andrew Yee
February 21st 06, 02:05 AM
Office of News Services
University of Colorado-Boulder
Boulder, Colorado
Contacts:
Carol Cleland, (303) 492-7619
Jim Scott, (303) 492-3114
Feb. 18, 2006
Search For Alien Life Challenges Concepts, Says CU-Boulder Professor
For scientists eying distant planets and solar systems for signs of alien
activity, University of Colorado at Boulder Professor Carol Cleland
suggests the first order of business is to keep an open mind.
It may be a mistake to try to define life, given such definitions are
based on a single example -- life on Earth, said Cleland, a philosophy
professor and fellow at the NASA-funded CU-Boulder Center for
Astrobiology. The best strategy is probably to develop a "general theory
of living systems," she said.
Many biologists agree the best definition of living systems today is the
"chemical Darwinian definition" involving self-sustaining chemical systems
that undergo evolution at the molecular level, she said. But the theory is
limited in that life on Earth probably resulted from physical and chemical
"contingencies" present at the time of its origin on the planet.
"What we really need to do is to search for physical systems that
challenge our current concept of life, systems that both resemble familiar
life and differ from it in provocative ways," she said. Cleland
participated in an astrobiology symposium at the annual American
Association for the Advancement of Science meeting held in St. Louis Feb.
16 to Feb. 20.
In 1976, for example, NASA's Viking 1 spacecraft conducted automated
biology experiments on Mars by mixing soil samples with radioactively
labeled nutrients to determine if metabolic "burps" from possible
extraterrestrial microbes could be detected, she said. Although positive
readings convinced at least some team scientists that life was present, a
subsequent investigation by a second Viking instrument failed to find
evidence of organic molecules on the planet's surface.
"Initially, the scientists were ready to break out the champagne," said
Cleland. "But because subsequent investigations yielded baffling results
that didn't fit the original metabolic definition of life they were
working with, NASA eventually concluded the original signal was not
evidence of life. This is an experiment that is still debated today, and
it's a classic example of an anomaly."
Out of more than 100 amino acids, terrestrial life constructs all of its
proteins from only about 20 of them, suggesting a single origin for life
on Earth, said Cleland. "It's very difficult to generalize about life
based on just one example," she said.
An article by Cleland and CU-Boulder molecular, cellular and developmental
biology Professor Shelley Copley, published online in the Jan. 16
International Journal of Astrobiology, explores the idea that an
"alternative microbial life" may exist on Earth. Such a "shadow biosphere"
could have a different molecular architecture and biochemistry than known
life and would be undetectable with current techniques like microscopy,
cell cultivation and Polymerase Chain Reaction amplification, the authors
wrote.
Despite new suites of sophisticated instruments developed in recent years,
the ability of scientists to detect life on Mars or in another solar
system is probably very limited, Cleland said. "If the DNA in an alien
organism was even slightly different than the DNA in life on Earth, with a
different suite of nucleotide bases to encode genetic information, we
probably wouldn't be able to recognize it."
So what might be out there? "It's not too far-fetched to imagine an alien
microbe whose genetic material directly and adaptively changes in response
to different environmental conditions," said Cleland. "Instead of looking
for life as we know it, scientists may be better served to look for
anomalies, which amounts to looking for life as we don't know it."
In the past decade, scientists have discovered more than 170 new planets
around other stars, a number that seems to grow by the month due to clever
new planet-hunting techniques, Cleland said. In the future,
astrobiologists surveying other planets will no doubt encounter non-living
systems that are "really weird," she said.
"In such cases, it probably is best to suspend judgment," she said. "The
great strength of science is its tentativeness, and through history, it
has been the careful analysis of anomalies that have eventually changed
scientific paradigms."
University of Colorado-Boulder
Boulder, Colorado
Contacts:
Carol Cleland, (303) 492-7619
Jim Scott, (303) 492-3114
Feb. 18, 2006
Search For Alien Life Challenges Concepts, Says CU-Boulder Professor
For scientists eying distant planets and solar systems for signs of alien
activity, University of Colorado at Boulder Professor Carol Cleland
suggests the first order of business is to keep an open mind.
It may be a mistake to try to define life, given such definitions are
based on a single example -- life on Earth, said Cleland, a philosophy
professor and fellow at the NASA-funded CU-Boulder Center for
Astrobiology. The best strategy is probably to develop a "general theory
of living systems," she said.
Many biologists agree the best definition of living systems today is the
"chemical Darwinian definition" involving self-sustaining chemical systems
that undergo evolution at the molecular level, she said. But the theory is
limited in that life on Earth probably resulted from physical and chemical
"contingencies" present at the time of its origin on the planet.
"What we really need to do is to search for physical systems that
challenge our current concept of life, systems that both resemble familiar
life and differ from it in provocative ways," she said. Cleland
participated in an astrobiology symposium at the annual American
Association for the Advancement of Science meeting held in St. Louis Feb.
16 to Feb. 20.
In 1976, for example, NASA's Viking 1 spacecraft conducted automated
biology experiments on Mars by mixing soil samples with radioactively
labeled nutrients to determine if metabolic "burps" from possible
extraterrestrial microbes could be detected, she said. Although positive
readings convinced at least some team scientists that life was present, a
subsequent investigation by a second Viking instrument failed to find
evidence of organic molecules on the planet's surface.
"Initially, the scientists were ready to break out the champagne," said
Cleland. "But because subsequent investigations yielded baffling results
that didn't fit the original metabolic definition of life they were
working with, NASA eventually concluded the original signal was not
evidence of life. This is an experiment that is still debated today, and
it's a classic example of an anomaly."
Out of more than 100 amino acids, terrestrial life constructs all of its
proteins from only about 20 of them, suggesting a single origin for life
on Earth, said Cleland. "It's very difficult to generalize about life
based on just one example," she said.
An article by Cleland and CU-Boulder molecular, cellular and developmental
biology Professor Shelley Copley, published online in the Jan. 16
International Journal of Astrobiology, explores the idea that an
"alternative microbial life" may exist on Earth. Such a "shadow biosphere"
could have a different molecular architecture and biochemistry than known
life and would be undetectable with current techniques like microscopy,
cell cultivation and Polymerase Chain Reaction amplification, the authors
wrote.
Despite new suites of sophisticated instruments developed in recent years,
the ability of scientists to detect life on Mars or in another solar
system is probably very limited, Cleland said. "If the DNA in an alien
organism was even slightly different than the DNA in life on Earth, with a
different suite of nucleotide bases to encode genetic information, we
probably wouldn't be able to recognize it."
So what might be out there? "It's not too far-fetched to imagine an alien
microbe whose genetic material directly and adaptively changes in response
to different environmental conditions," said Cleland. "Instead of looking
for life as we know it, scientists may be better served to look for
anomalies, which amounts to looking for life as we don't know it."
In the past decade, scientists have discovered more than 170 new planets
around other stars, a number that seems to grow by the month due to clever
new planet-hunting techniques, Cleland said. In the future,
astrobiologists surveying other planets will no doubt encounter non-living
systems that are "really weird," she said.
"In such cases, it probably is best to suspend judgment," she said. "The
great strength of science is its tentativeness, and through history, it
has been the careful analysis of anomalies that have eventually changed
scientific paradigms."