War of the Worlds
EVEN BEFORE scientists from NASA and Stanford University stunned the world last August by announcing that a meteorite contained evidence of past life on Mars, their research deviated a bit from run-of-the-mill science. For instance, the NASA team withdrew a paper submitted to a scientific meeting last March because they worried that "someone might ask a question that would force us to give away our major finding," says planetary scientist Everett Gibson of NASA's Johnson Space Center. "If you were on to the biggest scoop of your life, would you tell people?" And Stanford chemists who were asked to collaborate with the NASA group, by analyzing meteorite slices for compounds indicative of life, were not even told what they were looking at. Samples were dubbed Goofy, Mickey and Minnie.
But the unusual secrecy pales next to what has been happening in the six months since the announcement. It is normal for scientific claims to be criticized. Rebuttal follows, and eventually the original claim stands, falls or is modified. But the debate over the claim for life on Mars has become filled with acrimony, sometimes at the level of "you ignorant slut!" Both sides pretty much agree that the meteorite fell from Mars and landed in Antarctica 13,000 years ago. Then the shouting begins. One eminent meteorite researcher, who prefers to keep his invective anonymous, calls the NASA team "an inferior group of people [who] are setting the agenda for others who have real science to perform." NASA's Gibson calls one of his critics "someone who has been in this country for 32 years and hasn't held a permanent job."
This would all make for a fine spectator sport, except for one problem. As the bitterness of the debate stiffens positions, putting careers and reputations on the line, there is real concern about whether the claim of past life on Mars--which, after all, would be the discovery of this or any other millennium--will ever be properly sorted out. Chemist Edward Anders, one of the deans of meteorite science, worries that the bitterness "will work against the usual scientific process" and hurt efforts to find out whether the potato-shaped meteorite truly harbors evidence of life.
Already the polarization may be taking a toll. Soon after the August announcement, NASA slapped a temporary moratorium on distributing samples of the meteorite--known as ALH84001--to scientists until it can sort out all the requests (probably by late spring). In the meantime, what Jeffrey Bada of the Scripps Institution of Oceanography calls a "black market" in slices of 84001 has sprung up. "It seems like the only people who have gotten the remnants are ones who are likely to be supportive of the original findings," charges Bada. Researchers at Caltech, for instance, received a piece when a member of the original NASA team at Houston's Johnson Space Center visited last September. At next month's 28th Lunar and Planetary Science meeting in Houston, the Caltech geologists will present data that support the life-on-Mars idea. NASA's David McKay, who led the 84001 team, says, "I don't think we influenced their position."
Scientific disagreements usually get their fullest airing at professional conferences. There researchers present their most cutting-edge data (the stuff that gets published in journals is months if not years old). Then critics take their best shots. But with the bitterness surrounding the Martian meteorite, this crucial step in the scientific process may be undermined: organizers invite scientists who agree with their position, or researchers choose to attend meetings of the like-minded. Next month, for instance, at the planetary-science meeting, some 30 papers will address the question of life on Mars. "More than 80 percent will support our hypothesis," says Gibson. At the American Chemical Society meeting in San Francisco in April, a session on 84001 organized by Bada is expected to be mostly critical of the life forces. And skeptics have been "begging to be on the program" of a Mars workshop at JSC in April, says Bada, "but so far no invitation has been forthcoming. This is simply an awful way to conduct science."
Amid all the acrimony, it is easy to lose sight of the substantive debate over the Martian meteorite. The NASA-Stanford team offered four lines of evidence last August to support the conclusion that 84001 contains signs of ancient Martian life. First, the rock contains little globules of carbonate. These molecules could have gotten there when carbon dioxide that was dissolved in water (think seltzer) percolated through fissures in the rock; water is a requirement for life. Second, iron sulfide and a mineral called magnetite are in the rims of the globules; on Earth, primitive bacteria excrete such sulfides (consider them microbe droppings) or produce magnetite to serve as tiny internal compasses. Third, tubelike structures in the rock could be "nanofossils," the mineralized remains of ancient bacteria. Last, 84001 is full of organic molecules called polycyclic aromatic hydrocarbons; on Earth, PAHs are often the by-products of the decomposition of living things.
Unfortunately, no one can think of a definitive experiment that would prove not only that something in 84001 could have a biological origin--which no one disputes--but that it did. Each and every bit of "evidence" for ancient life can also be produced by chemical, geological or other nonbiological processes (table, page 58). That was the gist of an exchange of letters between scientists skeptical of the life-in-the-meteorite conclusion and the NASA-Stanford team in a recent issue of the journal Science, which published the original claim. Anders describes the NASA-Stanford team as "heading straight for biological interpretations without considering inorganic alternatives." As he added to NEWSWEEK, "They have a blind spot." The point-counterpoint is highly abstruse (don't expect to follow it if you don't know your greigite from your pyrrhotite). To take just two of the issues, the simplified version goes like this:
On the claim that the magnetite is a likely sign of life: Researchers led by John Bradley, an expert microscopist at MVA Inc. in Georgia, published a paper in December showing that the magnetite in 84001 takes the form of rods, ribbons and platelets. Some of the rods grew like a spiral staircase. On Earth, such magnetite is found at steaming-hot fumaroles (volcanoes without the mountain), suggesting that 84001's magnetite also formed at temperatures between 500 and 800 degrees Celsius. In that caldron, says planetary scientist John Kerridge of the University of California, San Diego, "life could not have survived." No, says McKay's group: a 1990 paper reports whiskery and ribbony magnetites produced by bacteria at normal temperatures.
On the claim that PAHs "can be the product of the decay of living matter," as McKay says: "Can be"? No question. But Anders dug up a paper from 1862 (he gripes that "no one pays attention to papers more than three years old anymore") showing that nonbiological matter easily forms PAHs, too. And Jeff Bada and Luann Becker of UCSD will soon publish an analysis showing that PAHs like those in 84001 are also in meltwater from Antarctic ice. The NASA team's response: yes, the PAHs could arise without life, but they are "also equally consistent with the decomposition of biological matter."
One needn't have a Ph.D. in logic to realize that something is amiss here. "The NASA team has tended to answer criticism by saying, "Yes, what you say may be true, but what about...' and then they introduce something extraneous," says John Bradley. "I detect some obfuscation." Planetary geologist Robert Walker of Washington University complains that the NASA group has "tried to shift the argument so that others have to prove that the observations are not due to fossil life." Usually, the burden of proof lies on those making the new claim. The NASA scientists have committed another unorthodoxy, in the eyes of critics: they admit that none of their four lines of evidence makes the case for life on Mars, but then assert that taken together they do precisely that. It's sort of like admitting that none of the four legs of a stool is long enough to reach a countertop, but claiming that all of them together will reach. "They lowered the standards of evidence rather than raised them, which is what you would expect for a claim this extraordinary," says meteorite expert Allan Treiman of the Lunar and Planetary Institute. In fact, NEWSWEEK has learned, the NASA-Stanford team got ahead of its evidence from the start, in the eyes of some: an eminent astronomer who advised Science on whether to publish the paper calls the first version "even more assertive. Even the title--something like "Life on Mars: Evidence From Meteorites'," which was eventually toned down to "Possible Relic Biogenic Activity in Martian Meteorite ALH84001."
No one charges that the NASA-Stanford team got its numbers wrong, or misread an instrument dial. The controversy turns, instead, on different, subjective interpretations of the same data. And that's about as personal as science gets. Still, says McKay, "I didn't expect that it would become so personal and exaggerated." Why has it? Treiman attributes the bitterness to a "profound fear" by meteorite scientists "of what this might do to our field. We're at the bottom of the pecking order in NASA's budget, and people are concerned that if this turns out to be as stupid as cold fusion we'll be out on the street."
Six months after it made headlines, the life-on-Mars claim is battered but still standing. "Meteoriticists are virtually unanimous in being highly skeptical," says Anders. But the farther you get from this discipline, the more scientists accept it. When Harry McSween of the University of Tennessee gives talks at universities about his finding that crystals in 84001 likely formed at temperatures too hot for life, "the questions I get from scientists are really hostile. They try to twist our data so that they will be compatible with the hypothesis of life." Next month those rooting for life on Mars will get more ammunition. NASA's Ev Gibson and colleagues will unveil data that 84001 contains "biofilms," he says, "organic molecules that drape across crystals when bacteria move. We will also present data showing that there is a chain of magnetite crystals within the carbonates, and that the chain is identical to those produced by [certain] bacteria."
While the case for life on Mars is far from settled, one thing is clear. The bitterness of the debate has hurt what used to be a congenial community, and has shown the public that, contrary to the idealized portrait painted in textbooks, "the scientific process is overprinted with personalities and personal prejudices," as University of Washington astronomer Don Brownlee says. Adds McSween, "We'd all like to think that science is perfectly objective, but it's an intensely hu- man experience." And that, of course, might give reason to hope life could evolve a bit differently on Mars.
Based on analysis of a Martian meteorite (above) found in Antartica, scientists offer four lines of evidence for ancient life on the Red Planet. Skeptics argue that each of the four has a nonbiological explanation:
ITEM EVIDENCE REBUTTAL
Carbonates They form in the They also form at
presence of warm very high tempera-
water, a prerequisite tures, such as those
for life, and contain in the cosmic impact
chemical byproducts that blew the rock
of living things off Mars
Nanofossils Electron-microscope Structures are too
images shoe tubular small to be microbial
shapes that look fossils; they may be
like tiny terrestrial artifacts of the ele-
bacteria tron microscope
Magnetite On Earth, some The structure of the
living bacteria pro- crystals is identical to
duce magnetite as an that of those formed
internal compass at volcanic vents, at
high for life
PAHs These organic mole- They also form dur-
cules form during the ing nonbiological
decomposition of reactions; they're
living things common in Antartic
ice, so they may have
come from Earth