by Marc Kaufman
As with McKay, contamination was a bedeviling issue for Hoover, so he has offered reasons to dismiss it as a problem. Many of his samples came from the Murchison meteorite, which has been a gold mine for researchers studying its amino acids and other organic compounds. As many as seventy amino acids have been identified in the meteorite, and some of them don’t exist on Earth. If those organic compounds are extraterrestrial, how could it be that the microfossils are all contamination from modern microbes on Earth, Hoover asks? Murchison fell in the heat and scrub of Australia, and much of it was gathered within hours or days. So why, Hoover asks, has he found remains of organisms known to coexist in places like Antarctica and the arctic permafrost? How could they have contaminated Murchison? Perhaps most telling, he says, is that the microfossils have no nitrogen, an essential element for life. Nitrogen is lost from the remains of organisms over hundreds of thousands of years, which strongly suggests the microfossils are ancient. How, then, could they be the results of recent contamination?
If Hoover’s analysis is right, why aren’t his microfossils on the front page of every American newspaper? The answer involves some complicated history as well, because claims of microfossils in carbonaceous meteorites are not new. In 1961, at a meeting of the National Academy of Sciences, Fordham University organic chemist Bartholomew Nagy and microbiologist George Claus presented evidence for what they said were “organized elements” embedded in mineral grain of the Orgueil meteorite (which fell on southern France in 1864) and the Ivuna meteorite (which fell in Tanzania in 1938). Both were the rare carbonaceous meteorites and Orgueil in particular was so loosely formed that it would dissolve in water. Nagy and Claus didn’t exactly say the “elements” were microfossils, but they provided supporting evidence that pointed in that direction. Other American and Russian researchers went further in asserting the meteorite contained remnants of extraterrestrial life. None other than Harold Urey, of Miller-Urey fame and a Nobel Prize laureate for other work, wrote in 1963 that “if found in a terrestrial object, some substances in meteorites would be indisputably regarded as biological.”
A fierce and cutting debate ensued for a decade before a consensus developed that those “elements” were either contaminants from Earth or nonbiological but oddly shaped minerals that had tricked the investigators. It didn’t help that one Orgueil sample from the Montauban natural history museum in France was found to have been intentionally or accidentally contaminated when someone drilled a hole and inserted coal fragments and seeds of a local reed, closed up the hole, and sealed it. As Hoover later wrote in a paper that began with a history of these events, “A few scientific works were subsequently published, but the suggestion of a hoax associated with the Orgueil meteorite won their debate and terminated serious scientific search for microfossils in meteorites for over three decades.” Hoover told me that with this history in mind, he didn’t want to take on American colleagues because he was afraid the association would eventually jeopardize their careers. He has instead turned to Russian scientists, collaborating with Alexi Rozanov, director of the Paleontological Institute of the Russian Academy of Sciences in Moscow, and working most directly at Marshall with Russian microbiologist Elena Pikuta.
Hoover began his microfossil work thinking he would reexamine some of the earlier meteorite samples for the “organized elements” described back in the 1960s, and he says he did confirm the initial detections—the ones that had been retracted by the original discoverers under professional fire. Yes, some of that meteorite was contaminated, Hoover says, but some of it was not and the two could be differentiated. He expanded his work to other carbonaceous meteorites and says he was completely surprised when he began to find the filaments and round coccoid shapes so common to the microbial world of Earthly bacteria. For some time he thought they were most likely modern contamination, but the chemical tests he did gradually convinced him they were ancient and extraterrestrial. Unlike David McKay, who did get worldwide attention followed by years of published critiques, Hoover’s work has infrequently been cited by other researchers. He has his ardent supporters, but the circle is small. To better understand why, I sought out the head of the astrobiology program at the agency’s Washington headquarters, Mary A. Voytek.
She began by praising McKay, who she said broke open the field of astrobiology, even if his conclusions remain controversial and not widely accepted. As she saw it, his team has continued answering critics with sophisticated lab work, and he continues to broaden his research and interpretations. “He has his work cut out for him—as he should, because of the importance of the discovery. I think he’s really important to the field, which needs crusaders like him who have strong convictions and do good science.” She paused and struggled to find ways to explain her different feelings about Richard Hoover.
“First off, it has to be said that the presence of microfossils is extremely difficult to demonstrate. You have to be very careful in asserting what you understand. You have to know so much about chemistry, biology, ecology to exclude other possibilities before you assert something could not be terrestrial and so has to be extraterrestrial.”
Regarding Hoover’s work, she argued that placing so much importance on the shapes of the objects is especially hazardous because circles, rods, and spirals are favored by nature, both in the biological and nonbiological worlds. What looks like a bacterial sheath, she said, could just as easily be a mineral formation. And then there’s the contamination issue. Despite Hoover’s arsenal of findings and extrapolations about why his samples are not and cannot be Earthly contamination, the field pretty much assumes that’s what they are. Voytek dismissed the value of his carbon-to-nitrogen ratios as a sign of ancient life because the measure can be so misleading. Contamination scourge Steele told me: “I see the things Richard sees all the time. Everything tells me they entered the meteorite after it fell to Earth.”
Voytek, who heads the NASA Astrobiology Program but doesn’t supervise or fund Hoover’s work, said the bar is extremely high for the kind of research Hoover has taken on, and that “in fairness to him” it’s extremely difficult to do. She also said that as a microbiologist herself who has seen deeply held understandings in the field turn out to be incorrect, she cannot 100 percent rule out the possibility that Hoover is finding extraterrestrial microfossils. But “the community,” she said, “has pretty much made up its mind that the work does not at this point support his conclusions.”
Voytek had recently been up at Svalbard with the program that Steele helped set up, which has researchers use the instruments now available to astrobiology to assess from both afar and from close up whether rocks and other formations show signs of biomarkers. The work, she said, is excruciatingly complex. Her team’s work on an object known to be a fossilized stromatolite, a primitive structure created by colonies of bacteria, illustrates the point. She said that using numerous instruments and working for days, the team was unable to conclusively prove it was in fact the structured remains of what once housed a colony of organisms—even though they already knew it was the case. She also suggested I look up a humbling 1982 paper in Nature by Jody Deming and John Baross, then at Johns Hopkins University and Oregon State University, that asserted active bacterial life had been found in a culture heated to 250 degrees centigrade. They had been researching the newly discovered worlds of “black smokers” at the bottom of the Pacific, hydrothermal vents where organisms lived in extreme heat. They brought samples of bacteria to the surface in pressurized containers and concluded they survived at those superhot temperatures in the lab.
Both scientists are very highly respected (and would later be selected to be members of the National Academy of Sciences) and their work was initially received with enthusiasm. But a researcher at the Scripps Institution of Oceanography, Jonathan Trent, was skeptical and so did some tests of his own in an effort to re-create the results. What he found was that all the measurements in the initial research were accurate in a sense, but that they were artifacts o
f the research itself rather than measurements of something that actually was happening. The sample had also picked up inadvertent contamination, which had not been sufficiently tested with controls. In other words, all the numbers were correct, but for reasons that had nothing to do with bacteria living in a medium heated well beyond the boiling point.
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Still, research over the past decade into the worlds of extremophiles, microbes, and fossils has proven that what’s true today often is overturned tomorrow, and what’s rejected today may be accepted tomorrow. That is certainly what Gil Levin, the other prominent researcher in the world of astrobiology to cry “Eureka,” hopes will happen. Levin has fought since 1976 to convince his colleagues and the public that the Labeled Release experiment on NASA’s Mars Viking landers, a “life-detecting” effort that he designed, operated and analyzed, had succeeded. NASA does not dispute that his results were consistent with the agency’s definition of what would constitute “life.” But NASA and the space community also decided that this definition had been incorrect. The reaction captured by his Viking experiment was proof of biological activity, he says, but many other scientists say it was the result of an unsuspected geochemical reaction on the Martian surface.
The extraterrestrial guide star Carl Sagan had been a key member of the old Viking “biology” team, and at first he found Levin’s results credible and compelling. Later he changed his mind, concluding they did not clear the high bar set by the standard he had done so much to popularize: “Extraordinary claims require extraordinary evidence.” Levin has turned Sagan’s admonishment on its head. “Something has happened in the last three decades. The claims are no longer extraordinary. My God, where do you go to find a place with no life? You can’t do that on Earth. In our days as freshmen in biology class, we were taught that life was a thin, delicate film over the surface of the Earth. Well, that’s now a lot of hullabaloo and we know life is everyplace—way above the Earth, on the Earth, way below the Earth, throughout the sea, under the sea, in rocks, down miles below… So it begins to seem as if life is an imperative. The big question is this: Is that imperative limited to Earth, or does it exist on Mars and elsewhere?” The answer, to his thinking, was obvious.
And it wasn’t just limited, primitive, or unchanging Martian life that Levin imagined. He was amused, he said, by those who argued that if Martian life were present, it would exist only in moist subterranean pockets, and that it would not have evolved at all. “Darwin must be flipping over in his grave when he hears that. How can you have life anyplace and have it isolated for billions of years without adapting, without evolving, mutating too as it did on Earth? All of what we’ve learned about life on Earth, together with what we have learned about conditions on Mars, shows that the claim of the extraordinary is now quite ordinary. I think it would be quite extraordinary if Mars were sterile. After all, we know Mars and Earth have always been exchanging rocks, we also know those rocks, by experimental evidence, could contain microorganisms alive and deliverable from Earth to Mars in viable form. So it would be very strange if Mars was not populated from Earth, or Earth from Mars, or both from a third source. Our claims have become ordinary, while the evidence has become extraordinary.”
First and foremost was the methane on Mars, strongly suggestive of current or past biology. Then the evidence for water, or shallow subsurface ice, on Mars today and strong evidence that it flowed freely and widely in the past. But even without flowing water, research into Earth’s extremophiles has shown that bacteria can live in the liquid veins of ice and in mineral crystals. Now we know Mars had a magnetic field—necessary to hold a protecting atmosphere—and of course there are the meteorites that just might have Martian microfossils in them. And most edifying to Levin, the Viking test that had always been used to dismiss his finding—Viking failed to find any presumed necessary-for-life organic material on Mars—has itself taken a pummeling. Thirty years before, Levin had argued that Klaus Biemann’s gas chromatograph mass spectrometer did not have sufficient power to pick up signs of low-level concentrations of organics. But Biemann was a respected MIT professor, and back then Levin had only recently earned a doctorate (in environmental engineering, from Johns Hopkins University). Biemann carried the day, with the help of lingering doubts about Levin’s experiment, including the strength of the reaction he detected. But now an exact copy of Biemann’s instrument had been tested in Antarctica and other harsh places where microbes are present but in limited supply, and it couldn’t find the organic compounds and life that other instruments determined were there.
In 2007, it was Biemann who was writing an outraged article in the Proceedings of the National Academy of Sciences to defend himself against a strong critique of his Viking work by veteran researchers Rafael Navarro-González of the National Autonomous University of Mexico and Christopher McKay of NASA’s Ames Research Center. Three years later, the two published a second paper asserting that, based on their Mars simulation work, Biemann’s instrument most likely destroyed the organics present when it heated the soil to 930 degrees Fahrenheit. The researchers also wrote that when they heated organics and Mars-like Atacama Desert soil in the presence of the oxygen-chlorine compound perchlorate, now known to be present on Mars, they had found small amounts of two chlorine-based organics. The same compounds were detected in trace amounts in Biemann’s Viking experiment but were dismissed as contamination from cleaning fluids. But the fact that Biemann’s results may well have been wrong doesn’t mean that Levin’s are right. That is the conclusion that McKay and Navarro-González reached, to Levin’s great frustration.
Many space scientists think Levin is something of a nuisance, someone who can’t let go of a flawed experiment and result. Others see him as a pioneer and dedicated scientist who properly won’t stand down. “Steelie,” for instance, who did so much to undercut the work of McKay, says that Levin is one of his heroes. “He got his findings, he trusted the instruments, and he held his ground,” he said. “I admire that.” Scientists will eventually come forward with evidence of what they are convinced is, or was, extraterrestrial life, probably of the microscopic variety. How will we know when it’s the real thing?
“Extraordinary claims require extraordinary evidence.” Sagan’s often-cited words have been used to bludgeon David McKay’s Mars meteorite conclusions, Levin’s Labeled Release results, Hoover’s Murchison microfossils. The common refrain: How could they make such grand claims based on incomplete or controversial evidence? While Sagan’s standard sounds right and may be entirely appropriate, the experience of at least one of these researchers shows just how difficult it will be to define and interpret. As McKay knows, but seldom says, one of the people given his initial Allan Hills 84001 paper to review for Science was none other than Carl Sagan. He read it, no doubt had questions, criticisms, and suggestions, and ultimately recommended that it be published. He was terminally ill then, but still by all accounts alert and actively engaged in his work. Clearly, Sagan saw ALH 84001 as important—even “extraordinary”—science that was worthy of the attention it would soon receive. But fifteen years later, it remains just not extraordinary enough.
7 PLANET-HUNTING
You would think that searching for exoplanets many light-years away would require the newest, most sophisticated telescopes. But Paul Butler, one of the world’s great planet hunters, has done some of his best work at an observatory formally dedicated in 1974 by Prince Charles in the Australian countryside. The telescope’s mirror is relatively small by today’s standards and the observatory has none of the power and élan of the Paranal facility used by Mike Mumma. The skies are far more likely to be clouded over and the telescope unusable at night than at other new observatories. It’s also in kangaroo country, which Butler and many Australians see as a less than pleasant feature since the animals frequent the nighttime pathways around the campus: A full-force kangaroo kick can kill a man.
But Butler loves the Anglo-Australian Observatory (AAO), twenty
miles outside the two-street town of Coonabarabran in New South Wales and next door to the dramatic and ancient volcano remains of Warrumbungle National Park. Some of its perceived weaknesses, he says, are invaluable strengths. Yes, finding extrasolar planets is hard, but it’s well within the capacity of the four-meter Anglo-Australian Telescope (AAT) glass. And because the observatory is no longer cutting-edge, and is in a distant location that American and European astronomers are not keen to put in the time to use, Butler has what he needs most—lots and lots of nights on the telescope. He spends three months a year at the AAO. That means he can study a star for hours, even days or weeks if he suspects there’s a planet circling it. Since he began coming to Coonabarabran, the self-proclaimed “Astronomy Capital of Australia,” Butler and the team he leads have identified and to some extent characterized 40 exoplanets. Worldwide, astronomers have found more than 500 exoplanets, and Butler has been in some way involved in about half those discoveries. He plans to planet-hunt for years to come, but now he has a new focus: the makeup or “architecture” of solar systems. That’s because discovering where exoplanets are in relation to their suns and companion planets is essential to determining if they’re habitable and could ever be home to extraterrestrial life.
The son of a Los Angeles policeman, Paul Butler is a tall, bearded man who loves jazz and wears long pants only when it’s below freezing. He’s been looking for exoplanets since the late 1980s, more than a half decade before a Swiss team announced the first detection, which soon after was confirmed by Butler and his colleagues. He’s away from his wife, his home, and his office at the Carnegie Institution in Washington more than half the year at observatories in Chile, Hawaii, and in the land of kangaroos (or, as he terms them, giant-tailed rats). He calls the AAT control area his living room because he’s been there so much and he feels that comfortable in it. It helps that the telescope is also just through a blackout door from the control room; at more sophisticated and more highly elevated observatories like the W. M. Keck in Hawaii, the control room is a two-hour ride down the mountain. The nighttime world of star- and planet-gazing exerts an almost gravitational pull on those captured by it, an endless desire to know more about the mysterious yet increasingly knowable vastness in which we live. “On clear nights, there’s absolutely nowhere I’d rather be,” Butler says.
