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What Other Scientists Are Saying About Today's "Life on a Comet" Claim

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This morning, several news outlets gave voice to an extraordinary claim: Comet 67P/Churyumov-Gerasimenko, where the spacecraft Philae awoke last month, could be home to alien life. But extraordinary claims, we all know, require extraordinary evidence. So guess what these morning’s claims were lacking!

To bring you up to speed: Astrobiologists Max Wallis and Chandra Wickramasinghe claimed at this week’s National Astronomy Meeting in Llandudno, Wales, that certain features of comet 67P—including its black hydrocarbon crust, subsurface ice, flat-bottomed craters, and smooth, icy “seas”—are the result of microbial organisms living beneath the comet’s icy surface. To quote Wickramasinghe directly:

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.


Emphasis mine, because the juxtaposition of “unequivocally” with “in my opinion” should tell you a lot about this morning’s news right off the bat. It also helps contextualizes the criticism Wallis and Wickramasinghe’s claims have received in just the past few hours, which can be condensed into two points:

  1. Wickramasinghe has a history of making wild and unfounded claims.
  2. This latest claim is wild and unfounded.

The first point has been made consistently by Phil Plait. In the past eight years, the astronomer-cum-blogger has devoted no fewer than nine posts to debunking Wickramasinghe’s spurious hypotheses (these include claims that alien fossils have been found in meteorites; that NASA is covering up evidence of life on Mars; and that SARS, and the flu, and a weird red rain in India, all come from space). “To put it delicately,” Plaited tweeted today, in response to this morning’s news of life on comet 67P, “outrageous claims aren’t helped by sloppy methods and fringe science.”


Other scientists have been more diplomatic in their criticism, but the upshot of that criticism is unambiguous.

According to The Telegraph, scientists affiliated with the Rosetta mission have dismissed the claims of alien life out of hand. Project scientist Matt Taylor called them “pure speculation.” Monica Grady, a co-investigator on Philae’s chemical-analyzing instrument Ptolemy, echoed Taylor’s criticism, dismissing the claims as “highly unlikely.”

Astrophysicist Jillian Scudder, who was present for Wallis and Wickramasinghe’s conference presentation, said the researchers offered “no extraordinary evidence” to support the claim of life on the comet.

Sarah M. Hörst—an assistant professor of Earth and Planetary Science at Johns Hopkins University, and an expert in complex organic molecules—told me that, while she didn’t attend the presentation, the features Wallis and Wickramasinghe point to in their press release and various interviews are “not necessarily sufficient for life or indicative of life.”


“The press release basically just says the comet has water and organics,” says Hörst. Neither of these observations is disputed, she says, but complex organics are easy to make if you have the necessary building blocks (methane, formaldehyde, ammonia, and carbon monoxide, to name a few), and you don’t need life to do it. She continues:

“We’re trying to understand the origins of complex organic materials in the solar system. Where are they created, where are they transported to. What does that mean for the origin of life on Earth, what could it mean for life elsewhere,” says Horst.” “The better we understand these processes, the better we understand habitability. This is one of the reasons that Philae and Rosetta carry mass spectrometers, to identify and inventory the organic content of the comet.” That we have spacecraft analyzing the makeup of an object in space is exciting in its own right, she adds, “but to say that life must be responsible for the complex organics they are seeing is fundamentally false.”


NASA researcher Thomas Gautier, who works on mass spectrometry for the Rosetta mission, tells me he agrees with Hörst’s assessment, and adds that he has seen no clues so far that support Wallis and Wickramasinghe’s conclusions. “This is pure speculation from the authors and I personally think it is highly unlikely,” he says. “Organic molecules are by no mean a proof of life as they can be very easily formed by many abiotics (without life) processes. The formation of abiotic organic molecules is well known in the laboratory and widely spread through the solar system.”

Is it possible that life is responsible for some of 67P’s features? Scientists think it unlikely, but yes, it is possible, in the way that any unsubstantiated claim is, technically, hypothetically, possible. But there remains a big empirical gap between the evidence at hand and what Wallis and Wickramasinghe are claiming, and the leap they’ve taken to cross it removes their claim from the “science” column, and places it squarely in the “speculation” column. As planetary scientist Andy Rivkin put it this morning: “We may emotionally prefer crazy-sounding theories or believe things on faith, but that’s not ‘science’ as best practiced. And that’s cool! Not everything has to be science. But science has to be science.”


Contact the author at and @rtg0nzalez. Top image by ESA/Rosetta/NavCam/CC BY-SA IGO 3.0.