You may be hearing some exciting news about comet 67P/Churyumov-Gerasimenko, the place where the Philae lander woke up last month. Astronomer and astrobiologist Chandra Wickramasinghe says that the comet's core might harbor singled-celled extremophile life! But while he could be right, you should take his comments with a comet-sized grain of salt.

Wickramashinghe and his colleague Max Wallis made a case for a life-filled comet at this year's Royal Astronomical Society's National Astronomy Meeting in Llandudno, Wales. Wickramasinghe's theory is tied mostly to the cosmic ice ball's structure and black crust. According to Wickramasinghe:

What we're saying is that data coming from the comet seems to unequivocally, in my opinion, point to micro-organisms being involved in the formation of the icy structures, the preponderance of aromatic hydrocarbons, and the very dark surface. These are not easily explained in terms of pre-biotic chemistry. The dark material is being constantly replenished as it is boiled off by heat from the Sun. Something must be doing that at a fairly prolific rate.

The fact that Wickramasinghe uses "unequivocally" and "in my opinion" in such rapid succession speaks volumes on its own. Beyond that, there are plenty of other reasons to be skeptical of this announcement, starting with the fact that the professor has a lengthy history of taking things that are possible and spinning them as if they are proven. He's a big fan of identifying extraterrestrial life.

Slate's Phil Plait has dissassembled some of Wickramashinghe's past work in great detail, specifically a pair of shaky assertions that fossils of extraterrestrial life had been found in meteorites. (They haven't.) Plait also notes Wickramasinghe's other floated theories, including that the flu and SARS both came from space. Possible? Sure, but there's no solid evidence to back up those claims.

It's also worth noting that many of Wickramasinghe's most headline-making claims (though not this one in particular) have come out of the Journal of Cosmology, a fringe publication with a peer-review process that is questionable at best, and in which Wickramasinghe once published a paranoid rave titled "Extraterrestrial Life and Censorship." The title pretty much speaks for itself.

Even if you set aside Wickramasinghe's past record, there are a few things worth noting about this specific claim. First, it comes from a speech at a conference—not a peer-reviewed paper. Second, as the Guardian notes, the Philae lander doesn't actually have a way to test for life; a proposal to add this goal to the mission was allegedly "laughed out of court" during the planning stages 15 years ago. The lack of appropriate sensors means Wickramasinghe's claims—sane or not—are inherently unverifiable. The best one can do is guess at whether the heart of Philaes comet is full of alien extremophiles. Maaaaaaybe it is! But then again maybe it's not!

His claims—sane or not—are inherently unverifiable

It's that core uncertainty that's at the heart of many of these types of claims about extraterrestrial life. While they have often not been proven false, they are far from being proven true. Exciting headlines like "Alien Life on Philae Comet, Scientists Say" are technically accurate and practically write themselves, but they blow the weight of such claims completely out of proportion. Scientists can "say" all kinds of things, but the real strength of the scientific method is when they don't just "say," but say, consider, peer-review, test, and test again. And on the alien life front, we are still waiting for that kind of certainty.

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