Come In, Mars

SINCE HUMAN BEINGS FIRST LOOKED into the face of the universe and saw only infinite night, we have wondered who was out there. Not what -- that was clear enough. Stars, maybe rocks like the one under our feet. But did anything laugh and cry, have children, build monuments? Was anything looking back wondering the same things about us? Those questions remain unanswered, but last week a team of scientists announced that after two years of staring into a 4.3-pound meteorite from our neighbor planet Mars, they had found indications of life. The microscopic organisms they say they found never experienced life the way we do. But if they're right, then more than 3 billion years ago they lived -- fed, reproduced, died. And the simple fact of their existence radically improves the odds that we are not alone in the universe.

The scientists working on the meteorite rushed to acknowledge the circumstantial nature of their evidence: complex molecules, crystals that look like those produced by bacteria here on Earth and tiny tubes that look like terrestrial fossil bacteria. Any single finding could be refuted, but taken together they were enough for the National Aeronautics and Space Administration to call a press conference last Wednesday, and for NASA administrator Daniel Goldin to brief the president on the possibility of life in outer space. That only added to the hoopla caused by a draft copy of the scientists' research leaked to the press well in advance of its publication in this week's issue of the journal Science. John Pike, the director of space policy for the Federation of American Scientists, gave his assessment: ""This is the biggest thing that has ever happened.''

A recovery team found the meteorite in 1984 on an annual mission to Antarctica, in the icy wasteland of the Allan Hills. Its designation, ALH84001, reflects that origin. But the meteorite's journey began 4 billion years earlier, when it was part of the crust of Mars. (Scientists know this because when the rock is heated, it still gives off a mix of gases unique to the Martian atmosphere.) The planet was a very different place then -- the air was about as thick as Earth's, the temperature was about the same and liquid water flowed on or near the surface.

About 3.6 billion years ago, blobs of minerals called carbonates were forming inside tiny cracks in the rock, spreading like hard-water deposits in pipes. Over time, Mars lost its atmosphere and liquid water vanished. Perhaps 15 million years ago, an asteroid or comet slammed into Mars and kicked up the clump of crust that would become ALH84001. It orbited the sun until 13,000 years ago, when it plunged to Earth.

From this unprepossessing chunk of rock, scientists have teased out a remarkable chain of evidence leading toward an astonishing conclusion. Team member Richard Zare, a chemist at Stanford, used lasers and an extremely sensitive detector called a mass spectrometer to spot molecules called polycyclic aromatic hydrocarbons. PAHs result from combustion; they are found in diesel exhaust and soot, even in many other meteorites. But they also come from the decomposition of living organisms. The residue in ALH84001, says Zare, ""very much resembles what you have when simple organic matter decays.'' The PAHs are deep inside the fissures in the rock, and their concentrations are much higher than in Antarctic ice. Both of these facts suggest that the PAHs came from Mars, not from space or Earth.

The team still needed to know whether the PAHs came from living things. The concentration of PAHs was highest near the carbonate globules, so the researchers put them under another high-tech sensor, an ultra-high-resolution transmission electron microscope. They found that the thin black-and-white bands at the edges of the carbonates were made of mineral crystals 10 to 100 nanometers across (the period ending this sentence is about 500,000 nm wide). Like PAHs, these minerals -- mainly iron compounds called magnetite and pyrrhotite -- can come from inorganic sources. But the crystals in the meteorite were shaped like cubes and teardrops, just like those formed by bacteria on Earth. In other words, they look like bacteria droppings.

The finding that transfixed researchers all over the world, though, was also the most vivid. Using a scanning electron microscope, which can resolve nanometer-scale details in three dimensions, David McKay and Everett Gibson Jr. of the Johnson Space Center focused on grains at the edges of the carbonate globules. At the press conference, McKay showed a slide of a cluster of elongated, tubular shapes with rounded ends. The smallest is about 20 nm long; the largest, around 200 nm. ""Are these strange crystals? Are they dried-up mud?'' McKay asks. ""We interpret that these are indeed microfossils from Mars.'' Comparisons with terrestrial fossils are equivocal. Pictures of 3i-billion-year-old bacteria from our planet look similar, but they are as much as 100 times larger.

The scientists, and NASA, are doing all they can to avoid another cold-fusion debacle, announcing a ""breakthrough'' at a press conference only to have it debunked. ""We have these lines of evidence,'' McKay says. ""None of them in itself is definitive, but taken together the simplest explanation is early Martian life.'' At their press conference, McKay's team pressed the need for further confirmation of their results. Other scientists agreed. ""It is provocative evidence,'' said astronomer and author Carl Sagan. ""It is not yet at the level where we can definitively say that microfossils have been found on Mars ... but I think some guarded optimism is quite realistic.''

Some scientists in the field express more optimism than others. Ralph Harvey, a geologist at Case Western Reserve University, and Harry McSween, a geologist at the University of Tennessee, have also studied ALH84001. In a paper in the journal Nature last month, they said that the carbonate globules formed at temperatures greater than 650 degrees Celsius, much too hot for any life we know of to exist. And alternative -- and mundane -- explanations exist for all the team's data. ""The question is whether the processes that might have made the magnetites and the organic molecules might have happened no matter what,'' says Allan Treiman, a planetary geologist at the Lunar and Planetary Institute in Houston, ""and whether all of them happening is more or less likely than having microbes in there.''

Fortunately, most of the questions about ALH84001 can be answered. If the microfossils are in fact long-dead organisms, the remains should include cell walls and cellular machinery. So far, no one has cracked one open to take a look, no easy task when your target is 20 nm across. McKay says the next step is to make ultrathin slices of the microfossils and try to find cell membranes or -- even better -- amino acids, the building blocks of DNA.

Still, most researchers agree that to really test these results we have to go back to the red planet. Meteorites haven't provided enough samples of the Martian surface -- of thousands recovered, only 12 come from Mars. Over the next 10 years, NASA is planning 10 robot missions to Mars, ""an armada of spacecraft,'' says Goldin. The Pathfinder, set to launch in December, is scheduled to land an automated rover on the surface on July 4, 1997. It's a tricky process, though. The most recent try, the Mars Observer, disappeared just before making orbit in 1993, and the latest Russian probes have also failed. Mars experts have been burned by surface probes too. In 1976 early results from the Viking landers seemed to show life in the sand and turned out to be wrong. As a result, scientists believe that ""sample return'' missions, where probes go to Mars and return with Martian soil, will be decisive.

Space scientists have been expecting E.T.s to show up for a while. In the past two years they've found seven planets in other star systems. Biologists keep finding colonies of bacteria in the most inhospitable places on Earth, such as undersea volcanic vents at 230 degrees Celsius. The threshold question in SETI -- the search for extraterrestrial intelligence -- is whether the evolution of life on Earth was a one-time event or the inevitable outcome of conditions that could exist on other planets. Any evidence of life on another planet, even as humble as bacteria, dramatically improves the numbers in the Drake Equation, which estimates the number of intelligent civilizations in our galaxy. ""The Mars discovery confirms the origin of life is easy, and will occur on planets where conditions are suitable,'' says Frank Drake, president of the SETI Institute.

So why the fuss over life that is 3.6 billion years old? Even if they turn out to be Martian microbes, they are long dead. The universe seems quiet again. But two kilometers under the Martian surface, say some scientists, is liquid water at a temperature capable of sustaining life. And if there were microbes under Mars billions of years ago, sky watchers like Drake wonder, what is there today? This search for answers, whether through religion, science or philosophy, is ultimately the search for our context, for our place in the universe. In the end, we don't want to stand alone.

Sparked by a lucky meteorite find, scientists used lasers, electron microscopes and detective work to tease out signs of Martian life from 3.6 billion years ago.


COPERNICUS, GALILEO, DARWIN: THE HISTORY OF SCIENCE IS STUDDED WITH DIScoveries that have made theologians rethink what the Scriptures say about the creation of the universe. The evidence introduced last week that microbes may once have existed on Mars hardly disturbed the universe of faith. But it did excite the imagination, especially of scientists who are also religious believers.

At the papal summer residence, where John Paul II was vacationing with a group of philosophers, astronomers from the Vatican Observatory were elated by the prospect of life outside planet Earth. ""Finding life on other planets is a vindication that God is not limited by our imagination,'' said Jesuit Guy Consulmagno, a specialist on meteorites. ""As our understanding of creation grows, our understanding of God gets bigger.'' At the Harvard-Smithsonian Center for Astrophysics, astronomer Owen Gingerich, a conservative Protestant, put the Martian find in Biblical perspective. ""In Genesis there's a sacred story being told that focuses on us. But there is nothing that precludes intelligent life elsewhere in the universe. It would be extremely arrogant to limit God's creativity to human beings as the only contemplative creatures in the universe.''

To be sure, it is a long way from a handful of molecules to intelligent beings with a will and conscience. There is, in fact, still no evidence to suggest that humankind is not alone among billions of galaxies. But to an astronomer like David Slavsky, dean of science and mathematics at Loyola University in Chicago, and a religious Jew, the message from Mars offers profound intellectual reassurance. ""I find it intellectually and spiritually uplifting to have evidence that the laws of physics and chemistry apply throughout the universe. It would be plain pre-Copernican to believe that life cannot occur anywhere else.''

If the laws of life are uniform throughout the universe, what about the laws of God? For Hindus and Buddhists, there is no problem: their cosmologies already teem with alternate universes inhabited by celestial beings. But the religions of the Bible clearly have theological questions to consider. Does the revelation of God on Mount Sinai apply to beings from another planet? If Christ died for the sins of a fallen humankind, would his death redeem beings from a distant galaxy? And must Muslims wage holy war with aliens to extend Islam? For Christians, Scripture may provide a clue. The New Testament proclaims that all creation was sanctified and redeemed through Jesus Christ. The Gospel of John presents Jesus as the Word of God who existed at the beginning of time -- and, therefore, presumably of space as well. ""It may be that God became incarnate in other forms elsewhere in the universe,'' suggests Jesuit Consulmagno. ""If we were to make contact with other intelligent life, we'd have to tell our own sacred story, listen to them tell theirs, and learn.''

To Slavsky, the mere possibility of intelligent life elsewhere in the universe opens up a new sense of community -- and an expanded notion of sacred drama. ""We already have a different sense of community than that which existed 5,000 years ago,'' he says. ""Today it means everyone on earth. Someday I hope we can extend that sense to a community of the universe.'' And what about God? Perhaps the Lord's reproving words to Job will still inspire awe. ""Where were you when I laid the foundations? Tell me, if you understand.''

Although the new evidence is compelling, there is a history of false alarms:

1877: An Italian reports seeing grooves (canali) on Mars, and a mistranslation fuels decades of speculation about ""canals.''

1961: A French meteorite yields what look like fossils. But wait -- don't those fossils resemble ragweed pollen?

1967: Radio astronomers find a pulsing radio source light-years away. A beacon from another civilization? No, but the source is the first pulsar discovered.

1976: The Viking landers titillate scientists with signs of life in Martian soil, until inorganic reactions offer a better answer.

Come In, Mars | News