Volume XXVII Number 1
"Snow euphoria" isn't merely an Earthbound phenomenon. Astrobiologists are keenly interested in ice on Mars and on the three moons circling Jupiter. Because ice is an insulator, scientists believe water could flow beneath it.
Photo by David Bricker
Lisa Pratt takes water samples at a depth of approximately one kilometer in the Lupin Mine, Nunavat Territory, Canada.
Photo courtesy Lisa Pratt
Life or Something Like It
The relaxed and amiable press conference turned awkward when a reporter from Bangladesh asked: "Did you find any dinosaurs down there?"
Indiana University Bloomington astrobiologist Lisa Pratt had been dispensing answers with ease to a linguistically diverse group of Voice of America reporters visiting Bloomington last year. But this reporter, assigned to tell the people of Bangladesh all about Pratt's research, gave the geological sciences professor pause.
As Pratt recollects the moment, she understood the reporter to have asked whether she's ever encountered a dinosaur fossil, but his confusion points to a general lack of knowledge about what it is, exactly, that Pratt and other astrobiologists do.
It's not that Pratt would ignore a dinosaur if she ran into one. It's just that after many years as a deep-Earth geologist, she's not accustomed to finding living things that big--or that extinct. When she's scouring the Earth's depths for new forms of life, Pratt instead expects to find creatures that fit into hairline cracks in rocks several kilometers below ground.
Bacteria. Fungi, maybe. No scaly Velociraptors or lumbering Diplodocuses.
"We're really looking for much smaller creatures--probably bacteria," Pratt gently told the reporter. "We haven't found any dinosaurs. Not yet."
Pratt is looking for new life on Earth, and on Mars. On Earth, she has a pretty good idea of what she'll find--microorganisms that bear a solid resemblance to life near the surface. Previously unknown organisms she isolates on Earth will surely be carbon-based. They will depend on the presence of water and use DNA or RNA as genetic material.
On Mars, however, astrobiologists face a different scenario. Expectations of what may be found there are a bit more ... open-ended. If life exists on Mars, it may not rely on water and carbon for growth and reproduction, let alone use something approximating DNA as its genetic material. What scientists find on the Red Planet may very well exceed their expectations. They won't find a dinosaur in a mineshaft--but they may find something similarly unlooked-for.
And that's the rub for Pratt and other astrobiologists. They don't exactly know what they'll find on Mars or elsewhere, if anything. Their only model is Earth, and scientists agree, our planet and its creatures represent just one of countless ways life can exist. If the space-borne, life-sniffing rovers scientists devise in coming years are too narrowly focused--too unimaginative--extraterrestrial life may writhe undetected just under the probes' noses.
To avert that frustrating possibility, the National Aeronautics and Space Administration's Astrobiology Institute (NAI) at Ames Research Center (near Mountain View, Calif.) has been convening scientists whose research is devoted to expanding the boundaries of life as we understand it. Pratt is one such researcher. Since joining the IUB geological sciences faculty in 1987, she has developed considerable expertise on what conditions permit the existence of life, and her study of kilometers-deep bacteria and other "life in extreme environments," as the field is commonly called, has earned her the respect of her peers and the helm of the NASA-funded Indiana-Princeton-Tennessee Astrobiology Institute.
IPTAI is one of 16 NAI "lead teams" that were each given $5 million in 2003 with one string attached: answer NASA's questions about how best to search for extraterrestrial life. IPTAI scientists at IUB; Princeton University; the University of Tennessee-Knoxville; the Pacific Northwest, Lawrence Berkeley, and Oak Ridge national laboratories; and others will confer with NASA scientists and engineers until at least 2008, when IPTAI's mandate will be up for renewal.
It may seem strange that NASA would hand the IPTAI directorship to a geologist whose research projects take her down, not up. But Pratt, who prefers to be called a biogeochemist--a title that reflects the multidisciplinary nature of her work--was easily the best choice for the job. One of IPTAI's key goals, after all, is to recommend to NASA how best to search for life deep below the Martian surface. Who better to advise the space agency than a geologist whose investigations routinely propel her across the Earth and into mine shafts two or three kilometers below its surface?
Pratt's extreme environments projects will also help sort out just how violent, toxic, and generally disagreeable an environment has to be before biological evolution fails to produce a species that can survive it. By drawing out reasonable boundaries for life, IPTAI scientists will help NASA honchos decide where life is most likely to be found. With each unmanned mission to Mars incurring a cost of $300 million, each future manned mission expected to cost hundreds of millions more, and NASA budget requests under intense Congressional scrutiny, NASA also needs to know desperately where it shouldn't be looking. Every taxpayer dollar NASA spends must be unassailable.
"One might ask whether the astrobiology endeavor is worthwhile," says NAI Director Bruce Runnegar. "As far as the institute's budget goes, it's easily justified by the kind of science we're doing anyway. Extremophiles [organisms that thrive under extreme conditions] in Earth's deep subsurface are part of our biosphere, which is something we know very little about. We'd all like to know more."
In 1961, the astronomer Frank Drake optimistically estimated that as many as 6 million intelligent civilizations may exist in the Milky Way galaxy. More skeptical turnings of the now-famous Drake equation (incorporating new knowledge of star system formation) put that number at 50. And that's just intelligent life.
Critics say such calculations are unreliable. Still, the voluminous number of stars in our universe seems to favor the odds that life is out there.
"The probability of ours being the only planet in the universe with life is very small, if life is an automatic result of chemical evolution," says Runnegar, who is also a professor of paleontology at the University of California, Los Angeles. "Science has helped establish that Earth is not the center of the universe in any substantial way. The discovery of extraterrestrial life would be another way of demonstrating that."
Runnegar says the time is finally right to find out just how far off-center humans are. The NAI and other astrobiology initiatives in the United States, Europe, and Asia are being driven by public and governmental support as well as advances in terrestrial and space-probe technology. "Astrobiology may be no more than 10 or so years old, but it's already attracted a lot of people who'd never been interested in the topic in a serious way before," Runnegar says. "What we have now is a young and extremely vibrant cross-disciplinary field."
While unquestionably a legitimate scientific field populated with top scientists, astrobiology's milieu--life in outer space--has yet to be found.
"That may seem a little odd," says Pratt, "but actually, an astrobiologist is really someone who is simply interested in the origin, evolution, and existence of life beyond the earth."
At present, there are only a few places in the solar system scientists consider possible past or present life-bearers. There is Mars, of course, whose poles are covered with ice and whose subsurface minerals are now known to contain water, albeit in a frozen or semi-frozen state. At Mars's equator, during what corresponds to high noon on a summer day, temperatures can reach 5°C (about 40°F). Water might melt, but Mars's thin atmosphere causes water to instantly vaporize or sublimate--in this case, go directly from solid state, ice, to water vapor.
Then there are the long shots. Literally. Jupiter's moon Europa, which had a cameo in the movie 2010, is covered with water ice. Since Europa is a pretty good-sized moon, scientists believe Europa has an active liquid core that radiates heat, possibly melting the bottom layers of Europa's ice sheath. Volcanic activity on Europa might spew sulfur-rich minerals from the bottom of the moon's hypothetical ocean, providing hypothetical life with a hypothetical source of energy. In 2000, the intrepid NASA satellite Galileo returned data to Earth that supported the existence of water not only on Europa, but also at or near the surface of Europa's neighbors Ganymede and Callisto. Ganymede is the solar system's largest moon, and Callisto is hardly a runt. The two moons are so big, they support thin atmospheres.
Conditions on Mars and the three Jovian moons are extreme, to be sure. They are extremely cold, extremely dry, and extremely thin, atmospherically. But not so extreme that astrobiologists are dissuaded from looking for signs of life there. After all, life is known to exist in some pretty weird conditions right here on Earth.
As recent as the 1960s, scientists believed the upper temperature limit for life on Earth was about 75°C (170°F). Then, in 1969, IU Bloomington biologists Thomas Brock and Hudson Freeze isolated a bacterium from Yellowstone National Park hot springs that could withstand temperatures as high as 100°C (215°F). The discovery of this new bacterial species, which the scientists named Thermus aquaticus (loosely translated, "in a lot of hot water"), kick-started life in extreme environments research.
Scientist-explorers began finding life in some pretty strange places, like at the bottom of the ocean, where there is no sunlight, pressure is intense, and among the only sources of available energy are hydrogen sulfide, carbon monoxide, and methane--substances which tend to poison life at the ocean's surface.
As part of her own life in extreme environments explorations, Pratt and colleagues at IU and Princeton have been looking for microorganisms in solid rock. To retrieve rock that may contain samples of these unusual microorganisms, Pratt's team regularly descends South African and Canadian mine shafts choked with noxious gases. If the scientists successfully isolate a new species from the deep subsurface rocks, they will expand Earth's known biosphere--and instantaneously increase the likelihood of life on Mars.
"We now know the surface of Mars is frozen, and the interior is hot," Runnegar says. "Somewhere in between, there must be liquid water. It's possible life could survive in that liquid zone if it can make use of the materials that are available. We don't know whether subsurface life can exist without any contact with the surface. Lisa's mine explorations will give us great insight into what is possible on Mars."
Pratt says that in these deep, subsurface zones, scientists expect "nutrient cycling"--the movement of water, minerals, and chemical foodstuffs--to occur very slowly. In these strange and oppressive conditions, life might happen, albeit in slo-mo. "We have to look at the deepest, hottest, coldest, most acidic, most alkaline places on Earth where life exists," she says. "These areas might mimic the kinds of environmental conditions most likely to support life on Mars."
In addition to the palpable impact life in extreme environments research has had on astrobiology, it has also endowed scientists with new optimism. Perhaps life can live in conditions that are a little drier, a little colder, a little weirder than we'd previously thought. Perhaps life can grow in intensely salty conditions, or without light, or under extreme pressure. (Perhaps life can live on pure adrenaline and coffee.)
If bacteria can grow and reproduce in boiling temperatures, and do the same in subzero temperatures in the Antarctic, scientists ask, why can't life grow and reproduce in similar environments on other planets and moons?
"If we are indeed the only place where life has evolved--and persisted--then this is an extraordinarily special place," Pratt says. "If, on the other hand, the origin and evolution of life is a frequent occurrence, then I suspect we're in for a rude surprise."
Answers may not arrive until humans have scoured the solar system. It is possible those efforts will turn up nothing. But even in the face of such a defeat, one thing, at least, seems certain. There are those who will remain hopeful, people who will shrug off defeat and turn their attentions to the boundaries of our celestial neighborhood, or whatever constitutes the next frontier.
David Bricker is a media relations specialist in the IU Office of Media Relations and a freelance writer in Bloomington.