Life in meteorites? Study stirs debate

A field-emission scanning electron micrograph shows one of the filaments that was found in the Ivuna CI1 carbonaceous meteorite. The image includes labels for data about elemental composition. The bar at lower left shows the 1-micron scale. The filament looks similar to those seen in earthly cyanobacteria.

By Alan Boyle

Are there traces of ancient bacteria trapped inside meteorites that fell to Earth decades ago? You can add that question to the list of unresolved issues surrounding the search for life beyond Earth, thanks to a just-published study by a NASA researcher.

The new study, published in the Journal of Cosmology, focuses on structures that look like the filaments that biologists typically see on micro-organisms known as cyanobacteria. Richard Hoover, an astrobiologist at NASA's Marshall Space Flight Center in Alabama, found the filamentary structures inside samples of meteorites that are thought to date back to the solar system's beginnings, more than 4 billion years ago.

If the structures are confirmed to be of biological but unearthly origin, that would serve as fresh evidence that life can make its way through outer space and "seed" planets, including our own, Hoover told me today.

"Life may have a wider planetary distribution than simply being limited to the planet Earth," he said. In the paper, Hoover said the evidence suggests that microbial life could well exist on comets or icy worlds such as Europa or Enceladus.

Most astrobiologists might be willing to go along with that broad conclusion. However, Hoover's specific claims could well end up in the same sort of limbo that surrounds the claims made 15 years ago about microfossils inside a meteorite from Mars.

The initial evidence was the subject of dramatic news conferences and huge headlines, but as time went on, doubts about the findings grew. Today, few astrobiologists see the Mars meteorite as containing any conclusive evidence for the existence of past or present Martian life.

Cautious and skeptical reactions
"This may turn out to be another one of those cases where it's controversial but remains unproven," Seth Shostak, senior astronomer at the California-based SETI Institute, told me today.

Shostak said Hoover's findings would be "important, if true." But he noted that the research paper relied on a highly technical interpretation of electron microscope images and chemical analyses. "Is it true? I'm not qualified to say that," Shostak said.

The Journal of Cosmology's editor-in-chief, Rudy Schild of the Harvard-Smithsonian Center for Astrophysics, said in a note accompanying Hoover's study that 100 experts were invited to critique the research, and that any commentaries would be published beginning Monday. The overall tone of the commentaries is likely to be skeptical: Lynn Rothschild, an astrobiologist at NASA's Ames Research Center in California, said many biologists were "very concerned" about the claims.

More than one expert wondered why the research merited any news coverage at all.

"Many scientists have examined thousands of meteorites in detail over the past 50 years without finding any evidence of fossil life," David Morrison, senior scientist at the NASA Astrobiology Institute at Ames Research Center, told me in an e-mail. "Further, we know a great deal about the conditions on the parent objects of the meteorites, which (not counting the few meteorites from the moon and Mars) were rather small, not at all like planets.

"I would therefore invoke Carl Sagan's famous advice that extraordinary claims require extraordinary evidence. At a bare minimum this would require publication in a prestigious peer-refereed scientific journal — which this is not. Cyanobacteria on a small airless world sounds like a joke. Perhaps the publication came out too soon; more appropriate would have been on April 1," Morrison said.

Questions about origin
The debate over the validity of Hoover's claims is likely to concentrate over whether the filamentary structures are truly biological in origin, and if so, whether they're the result of earthly contamination.

Hoover said that the filaments, which can measure more than 20 microns long, are of the right size and shape to match the characteristic structures seen in types of cyanobacteria.

"Because of the fact that they are so large and so complex, and many of them have specialized cells, these cyanobacteria can be identified — sometimes to genus and species — just on the basis of certain specialzed cells," he explained. One of the structures found in the meteorites is similar to that seen in the giant bacterium known as Titanospirillum velox, for example.

If the structures are so similar to those seen in earthly organisms, could that be because they're actually the traces of cyanobacteria that found their way into the meteorite? Hoover argues that they're not the result of contamination. He said that cyanobacteria are generally found in aquatic environments, but the meteorites are made of stuff that falls apart when exposed to liquid water. He also said chemical tests on the filaments could find no evidence of nitrogen, which should have been present if earthly cyanobacteria infiltrated the meteorites. One of the meteorites, for example, is known to have fallen to Earth in France in 1864.

"The inability to detect nitrogen in the filaments indicates that they are ancient, and since the meteorite came to Earth in 1864, that indicates that they were in the meteorite when it fell," Hoover said.

Previous analyses of the meteorites' chemical composition have concluded that they were formed during the solar system's earliest epoch, perhaps as comets. But Hoover said that doesn't necessarily mean the structures were present from the very beginning. They could have been picked up from debris that was knocked into space by cosmic impacts. They could even have come from Earth itself, as the result of a meteor blast that occurred millions or billions of years ago.

"That's absolutely possible," Hoover acknowledged. "I have no reason to say I could rule that out."

Hoover has made provocative claims before, and he fully expects that others will contest his conclusions this time as well. "I can only make my observations, based on the scientific results that I see," he told me.

What do you think? Is this a significant advance for the study of life beyond Earth, or a blip hardly worth writing about? Feel free to weigh in with your comments below.

Update for 6 p.m. ET: Rocco Mancinelli, senior research scientist at the Bay Area Environmental Research Institute, weighed in with this e-mailed critique of Hoover's paper:

"As a microbiologist who has looked at thousands of microbes through a microscope, and done some of my own electron microscopy, I see no convincing evidence that these particles are of biological origin.  

"The techniques used may not have been appropriate for these types of analyses. It is stated that the implements were flame-sterilized, with no details of how this was performed.  Were the implements placed in the flame of a Bunsen burner? If so, sometimes soot can get on them at the microscopic level. The usual procedure for flame sterilization is to dip the implements in ethanol then burn the ethanol off. Yet, these would be inappropriate for this type of analysis. You need to have everything clean and then bake at 550 degrees C overnight.  These missing details would cause me to question not just about the photos, but the elemental analyses as well.  I am also disturbed about the lack of nitrogen. There should be more. There are many technical flaws in this paper."