The Search for the Scum of the Universe
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
21 May 2002
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.
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.
Other perils
Back at the STScI meeting, other dangers to life in the universe were laid out. Not all stars are as hospitable as our Sun, astronomers said. And we've not yet found anything close to an Earth-like planet. While it seems likely that solar systems like ours will be found, no one is certain that planet formation proceeds elsewhere as it did here.
In fact, most stars are now thought to have formed in clusters, where violent interactions may snuff out planet development altogether, said John Bally, an astrophysicist at the University of Colorado.
Those planets that do develop must travel through a narrow band of space around their host star, a so-called habitable zone where the temperature is just right, if they are to foster life as we know it. Worlds outside these zones would have to rely on some sort of internal heat to support life.
James Kasting, a top expert on habitable zones from Pennsylvania State University, said a mere 5 percent difference in position for most hypothetical planets around nearby stars would cause their oceans to evaporate away.
And Kasting also points out that if we cannot travel to a planet outside our solar system -- and we can't with today's technology -- then an inhabited planet is irrelevant if its life is below the surface and does not alter the chemistry of the atmosphere enough to be detected from afar.
Efforts to find life on Mars have proved that. Researchers still cling to the possibility that Mars may harbor life in its soil or rocks, but after three decades of exploring the planet from above and even at ground level, the question is still open.
Think like a Martian
Whether there are Martians or not, Nealson, the geobiologist says it's time to start thinking like one.
In his view, the meaning of "life" has to be pondered from a non-Earth-centric viewpoint if scientists are to have any hope of finding life elsewhere.
Nealson says human researchers are saddled with a "biological bias" that limits their collective ability to detect life to varieties they already understand. He argues that new methods need to be developed that would identify physical and chemical signatures of life, rather than attempting to directly examine biology.
One approach would be to look for chemical reactions occurring over a matter of days when, without some sort of life as a catalyst, "they wouldn't happen in a thousand years."
Another method -- viable only for planets we can travel too -- would involve looking at how the chemistry of a body of water or a layer of sediment changes with depth. Every example on Earth exhibits a common "stratification" chemistry, he said.
"If you build Captain Kirk's tricorder [a rather magical scanning device], all it has to do is measure the profiles," he said.
Nealson said no Mars mission prior to 2009 has the tools necessary to search for life in this way. He argues that the prospects on Mars beg for testing new methods of looking for life no matter what it looks like.
It will be at least a decade before planned space-based telescopes will have the ability to crudely examine the atmospheres of distant planets for clues to the sorts of reactions Nealson discussed.
Smarter than scum
There is a potential shortcut to all these efforts. If life is more advanced, it would be relatively easy to find. In fact, "If life is advanced, it's going to find you," Nealson said.
An interesting idea, and one the folks at the SETI Institute have thought a lot about.
Jill Tarter, director of the institute's Search for Extraterrestrial Intelligence, said the effort is a branch of astrobiology that seeks to take advantage of the deliberate actions of other intelligent life, which she defined as civilizations that possess advanced technology capable of communicating electronically across light-years of space.
If anyone is sending signals our way, Tarter and her colleagues hope to detect them with increasingly creative approaches, from chunks of time at various telescopes around the world to a planned array of inexpensive antennas that would do other radio astronomy while simultaneously searching full-time for alien signals.
For now, SETI surveys a mere dot of sky compared to the vast reaches of our galaxy.
Nonetheless, if SETI finds a repeatable signal -- a true non-natural communication that can be verified by multiple detections -- astrobiology's biggest question would be answered in a flash. But it would also raise an issue that not too many astrobiologists were thinking about.
As Tarter pointed out, civilization on Earth represents the lowest form of technological advancement by the SETI definition. We've only been able to communicate electronically for a few decades. If there is anyone else out there with technology, sheer odds suggest they've had it much, much longer than we have. To them, we might be viewed as the scum of the universe.
"We really are the dumbest folks in the galaxy," Tarter told her esteemed colleagues.
