March 5, 2011 at 5:31 PM ET
Last updated 4:20 p.m. ET March 6:
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."
Update for 10:50 p.m. ET: Dale Andersen, principal investigator at the Carl Sagan Center for the Study of Life in the Universe at the SETI Institute, sent his detailed reaction in an e-mail:
"I would be absolutely thrilled to see this story verified, and it would be even more exciting if we found evidence of life that was quite different from terrestrial life — say, for example, its genetic coding used different base pairs than Earth life. That would imply not just evidence of life from beyond our planet, but would demonstrate an independent genesis of life, something that would be absolutely astonishing.
"That said, one needs to look at this paper with a lot of caution, particularly with [the Mars meteorite] ALH 84001 in mind. That was a great story and generated a wonderful debate that continues even today — regardless of the outcome, I would say it was a success story. The best of the best have worked on that meteorite and tried in vain to prove or disprove the original thesis that ALH 84001 holds evidence of life from the planet Mars. While I think it's fair to say that the general scientific consensus is that McKay et al. [the researchers who did the Mars meteorite study] did not provide unambiguous evidence of extraterrestrial life, the process that accompanied the effort throughout was well worth the effort. The scientific community was compelled to think in new ways and to find better tools and methods to examine the evidence. This resulted in technological advances and a much better understanding of how to approach the problem and finding its answer. And the public was very engaged throughout, which was a good thing. I hope there is long-term, strong support for NASA's Exobiology program and that NASA is allowed to continue the search for a better understanding of the origin, evolution and distribution of life in the universe; it's a goal worthy of support.
"With respect to Richard Hoover's claims about finding evidence of life within the samples of meteorites he has observed, I think he has a very high bar to clear before this story is accepted by the scientific community. It should also be noted that Richard has published this thesis previously (e.g., in 2004:"Perspectives in Astrobiology" (NATO Science Series: Life and Behavioural Sciences, Vol. 366) [Hardcover] Richard B. Hoover (Editor), Aleksei Iurevich Rozanov (Editor), Roland Paepe (Editor)), and the ideas were not well-received nor did they gain traction within the scientific community.
"Peer review will include the examination of his and other scientists’ data and logic, and not until that has occurred will we see how the story unfolds. Occam's razor will eventually be used to slice and dice the carbonaceous chondrites used by Richard to present his evidence. Is it more likely that upon looking into the interior of a meteorite collected on Earth and finding photosynthetic cyanobacteria, which on Earth are usually found in water or wet sediments, their presence is due to contamination from terrestrial sources or that it formed inside the parent body of comet or asteroid in deep space? There will be many other possibilities to rule out before one arrives at the extraterrestrial answer.
"I hope the public does not assume that this story is a certainty — it clearly is not, at least not at this point. Mostly, I hope the general public is able to learn more about the scientific process and the use of critical thinking skills to arrive at the truth and are not confused by an endless parade of silly articles that neither enlighten nor inform. Let the debate begin.
"A side note: I am not an expert with respect to meteorites. It would be very useful to get some of the ALH 84001 folks to weigh in on Richard’s findings, techniques, histories of the meteorites used (where collected, handling), logic etc. And while it may be OK to express healthy skepticism in public forums — meetings such as AbSciCon, AGU, AAAS, etc. and the scientific literature are the places to really rebut and critique the body of work presented — the scientific process should be the judge. Perhaps that is the real story here. Let the facts demonstrate the truth."
I e-mailed an inquiry to David McKay, one of the leaders of the ALH 84001 research team at NASA's Johnson Space Center, even before Andersen mentioned the idea — and I'll report back if I hear anything.
Update for 3 p.m. ET March 6: More critical commentaries are coming in, from Pharyngula's P.Z. Myers as well as from Rosie Redfield, the microbiologist at the University of British Columbia who blew the whistle as well on the "arsenic life" research that made such a splash last December. Here's a link roundup:
Update for 4:20 p.m. ET March 6: Rudy Schild, the astrophysicist at the Harvard-Smithsonian Center for Astrophysics who is also the editor-in-chief of the Journal of Cosmology, sent this open letter via e-mail today:
"The Journal of Cosmology had issued a personal invitation to 100 scientists, and a general invitation to over 5,000 members of the scientific community, inviting critical commentary on Dr. Hoover's landmark, paradigm shattering paper. All were given access to a PDF containing a preprint of Dr. Hoover's article.
"Within hours of making it available, it was downloaded over 1,400 times.
"After issuing an open invitation for scientists to search for flaws and to report them in a scientific forum, as of March 6, the Journal of Cosmology has received 12 commentaries.
"Five detail what could best be described as minor quibbles. One offers an alternative explanation as to the origin of these fossils but does not dispute the evidence. We will publish all commentaries so far received, this evening.
"It is natural to have doubt. Skepticism is the nature of science. Debate is healthy and is good for science. We are frankly amazed that we have not received an avalanche of critical commentaries.
"Perhaps the reaction could be described as 'stunned silence'?
"As to those who post insults on various websites, this is not to be taken seriously.
"On the other hand, Dr. Hoover's article, and the lack of scholarly, critical dispute, may be an indication of a paradigm shift; similar to the realization that Earth was not flat nor the center of the Universe. What I mean is: Most scientists and perhaps most of the public realize life must be everywhere throughout the cosmos and not just confined to Earth, and Dr. Hoover's paper simply confirms what most already suspect.
"This may also account for why the over 150 news articles and blogs so far published (with the exception of MSNBC), the response has been generally favorable or positive in nature.
"The inability, so far, of the scientific community to find and present any major flaws in a scientific forum and to submit and publish them in a scientific Journal which has invited critical commentary, speaks for itself.
"However, the jury is still out. Our deadline for receipt of scientific commentaries is Monday, the 7th. We will extend that deadline.
"The Journal of Cosmology will publish critical commentary. We encourage it. We ask the media to encourage the scientific community to send us critical commentary.
"However, so far, the verdict appears to be: We are not alone."
Earlier, Schild forwarded some additional reactions to Hoover's paper. Here is a quote attributed to Carl Gibson of the Center for Astrophysics and Space Sciences at Scripps Institute and the University of California at San Diego:
"Dr. Hoover has provided the world with extraordinary evidence to back up extraordinary claims. This discovery completely changes our perspective of the nature of life and our place in the universe. The world will never be the same."
Here's a quote from Chandra Wickramasinghe, director of the Astrobiology Centre at Cardiff University, who has also stirred up controversy for his views about life from space:
" Dr. Hoover has provided the world with decisive evidence that we are all aliens. Life is a truly cosmic phenomenon. ... We believe Dr. Hoover's evidence, coupled with other findings and recent genetic studies, indicates life has a genetic ancestry which leads over 10 billion years back in time. Some of these life forms were delivered to Earth, in comets."
I've started up a new item with further reaction, from the Journal of Cosmology's commentaries as well as other sources.
More controversies in astrobiology:
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