[UPDATE (March 7, 2011): I've posted a followup on this news with a much more detailed analysis, and not too surprisingly the scientific consensus coming in is that the claims of alien fossils are way wrong.]
Richard Hoover, an astrobiologist at NASA's Marshall Space Flight Center, thinks he may have found bacteria in a meteorite.
Yes, you read that right. The question is, is he right?
I don't know. Dr. Hoover has published his findings in the online Journal of Cosmology (see below for more about this journal), and it was reported today by Fox News (thanks to Sheril at The Intersection for the tip).
Basically, Hoover found structures inside a rare type of meteorite -- the Orgueil meteorite which fell in France in 1864 -- that look very much like microbes of some sort. Here's an example from the paper:
Those are odd and intriguing formations, to be sure. If I were scanning through a meteorite and saw those, I'd be pretty surprised too.
But appearances can be deceiving. Are these actually fossilized microscopic life forms?
Hoover makes several claims to show that a non-biotic origin for these structures is very unlikely. I am not an expert and won't cast my vote either way here. This is not the first time Hoover has made such claims; he gave a similar presentation in 2007. There have also been many similar claims in the past. In fact, in the second episode of "Bad Universe" I interviewed NASA astrobiologist Dave McKay, who has also found very interesting features in a Mars meteorite that look a lot like bacteria. However, definitive proof is another matter. McKay's opinion is that what he found was once alive, but he also was clear that scientifically he could not be sure (I found his skepticism to be well-grounded and at the right level, to be honest).
Probably the biggest bump in the road for showing these things are life-forms is to show they are not the result of Earthly bacteria getting inside the meteorite after it hit. This is very tough to do, though Hoover says this in his paper:
Many of the filaments shown in the figures are clearly embedded in the meteorite rock matrix. Consequently, it is concluded that the Orgueil filaments cannot logically be interpreted as representing filamentous cyanobacteria that invaded the meteorite after its arrival. They are therefore interpreted as the indigenous remains of microfossils that were present in the meteorite rock matrix when the meteorite entered the Earth's atmosphere.
Clearly, Hoover thinks terrestrial contamination is unlikely. However, contamination, no matter how unlikely, is a more mundane explanation than extraterrestrial life, and Occam's Razor will always shave very closely here. We have to be very, very clear that contamination was impossible before seriously entertaining the idea that these structures are space-borne life.
I'll be honest: my own reaction is one of extreme skepticism. As it should be! All things being equal, I would take news like this with a very large grain of salt, and want a whole lot of outside expert analysis; I'd like to see other biologists examining the original meteorite, too. Interestingly, the editors for the journal in which this paper is published understand how controversial this claim is, so they have asked 100 expert scientists to review the work and critique it. Those reviews have not yet been published, so we'll see; the editors say the reviews will go online in a few days.
Also, I feel I need to mention this as well: in my opinion, The Journal of Cosmology has published articles in the past that can charitably be called "shaky" (like this anti-Big Bang paper). One of their editors, Chandra Wickramasinghe, has made some pretty outrageous claims about NASA and life in space (links to some of his other odd claims can be found at that page as well). However, this does not necessarily mean that Hoover's work is any more suspect than any other scientific claim! But it does mean I will cast an especially-skeptical eye on claims made in papers published by them. Others agree as well.
And I must note that in an error-laden article*, the Journal published a not-very-flattering comment about me, calling me an "astronomer-wannabe" -- heh-- and claims I led a "torches and pitchforks crowd" about the existence of a planet in the outer solar system. That's completely false, and in fact I got an email from the researcher leading the search for that planet, calling my article on it "the most balanced discussion" he saw!
[Updated to add: I've been informed the Journal of Cosmology is going out of business. They wrote a press release that may be of some interest.]
So, to conclude: a claim has been made about micro-fossils in a meteorite. The claims are interesting, the pictures intriguing, but we are a long, long way from knowing whether the claim is valid or not! We've been down this road before and been disappointed. As with any scientific claim, skepticism is needed, and in the case of extraordinary claims, well, you know the saying.
* Not once, but twice, the article states that WISE data exist which support the idea of a planet in the outer solar system ("...This model coupled with data from WISE, indicates the presence of a gas planet..." for example). That is simply wrong; the actual truth is that no WISE observations analyzed so far show any sign of such a planet.