Odds of Life The odds for extraterrestrial life on Earth-like planets will be put at 1-in-3 in a soon-to-be published report in the journal Astrobiology, but the smartest earthlings have no clue what that life might look like or where to find it.
In fact, at a meeting earlier this month of about 100 chemists, biologists, astronomers and other highly evolved thinkers interested in finding extraterrestrial life -- the scientists were said by one attendee to be the cream of the crop in their respective fields -- none could even say how the simplest life begins.
"Nobody understands the origin of life," said Ken Nealson, a geobiologist at the University of Southern California. "If they say they do, they are probably trying to fool you."
Nealson and the other scientists converged at the Space Telescope Science Institute (STScI) in Baltimore to discuss the fledgling field of astrobiology. They argued a little about how to conduct the search and whether life might be rare or common in the universe. However, they agreed on several things: They don't know how life might commence elsewhere, or whether it ever has, or what it might thrive on.
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 | Life? Microcystis aeruginosa is a type of cyanobacteria found on Earth. It is an algae known to cloud the Chesapeake Bay when it blooms and forms thick mats. Life on other planets might never have evolved beyond such simplicity.
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| Europa, a Jovian moon, is in half shadow in this color-enhanced image from the Galileo spacecraft. The cracks in the icy surface are thought to be caused by heated up-wellings of the water below. Microbes similar to those found in the Earth's ocean floor may exist on Europa. Click to enlarge.
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In addition, Nealson said, they don't even know how to look for it.
Odds are, the first ET we will stumble upon will be microbial. Because advanced life on Earth took billions of years to evolve, most experts figure the likeliest extraterrestrials are simple critters that can survive harsh conditions that make Alaska and Death Valley look inviting.
In that sense, astrobiology is first and foremost a search for the scum of the universe.
What is life?
The hunt begins here on Earth, where microscopic bugs have shown themselves to be far more tenacious and resourceful than anyone imagined just two decades ago.
"Life hides under rocks. Life hides in the rocks," Nealson said, adding that it has even learned to eat and breathe rocks, shunning more traditional foods and even oxygen. New
methods of survival turn up each year. On other planets, entirely different methods of getting by may have developed.So Nealson, also a researcher at NASA's Jet Propulsion Laboratory and considered one of the founders of astrobiology, has developed a short list of what he considers universal aspects to life.
"It'll have shape and composition. It'll have structure," Nealson said, because these characteristics are necessary to convert one type of energy to another, a process he considers fundamental to life. He continued: "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."
Beyond these features, Nealson said there is little else to distinguish life in a universal sense. It needs fuel, such as oxygen, but there are many chemicals that could serve this purpose. Life is thought to require water, but even that is not certain.
"One could imagine other solvents," he said.
Mars may or may not harbor life, and it is an important target on the astrobiologist's dartboard. So is
Europa, a moon of Jupiter. Even hot Venus and Saturn's methane-laden moon, Titan, have not been ruled out.But none of these places is much like Earth. Therefore, much of the hope in astrobiology is pinned on efforts to find other Earths. Most experts
fully expect to eventually discover some, yet present technology cannot detect Earth-sized planets in Earth-like orbits around other stars.ET and the biogenetic lottery
Meanwhile, Charley Lineweaver and Tamara Davis of the University of New South Wales decided to look more deeply into a notion that is often repeated but seldom backed up with real analysis: Given the rapid appearance of life on Earth, one might expect life to exist on other worlds with similar conditions.
The researchers considered just how long it did take life to get going -- much less than a billion years, they say -- and therefore how common such a process might really be throughout space.
Lineweaver and Davis will report in Astrobiology that 1-in-3 Earth-like planets more than 1 billion years old could have developed life.
The approach to their calculations is fairly simple. More probable events happen more often, and therefore more rapidly. Life on Earth began shortly after the planet is thought to have had all the ingredients necessary, an era that was also relatively soon in the planet's 4.5-billion-year history. We "won the biogenetic lottery" soon after it was possible, they say.
Earth's good fortune implies, statistically, that it is a fairly easy lottery to win and should be won by other entrants -- 33 percent of them as it works out.
In the paper, the researchers point out several possible pitfalls to their argument. If there is only one life-harboring planet in the universe, for example, "we would, of necessity, find ourselves on that planet."
A more significant caveat, Lineweaver said in an e-mail interview, is that "the origin of life and the beginning of molecular evolution may have to take place early if it is to occur at all." Other researchers have suggested that life was
jumpstarted by frequent and intense impacts from asteroids and comets, a feature of our early solar system that is no longer the case.Lineweaver and Davis also point out that odds are just that, odds, and they do not necessarily mean that life is common in the universe.
Next Page: Other perils, and why we should think like Martians
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