An image taken by the Philae lander as it descended toward 67P. Credit ESA

So. Here we go again. More amazing claims being made in the media, and this time, it's about alien life. Earlier today, a number of sites started posting articles about the Rosetta mission and, more pointedly, the Philae lander. The titles mostly go a little something like this, "Alien Life On Philae Comet, Scientists Say." And the claims mostly go a little something like this: "Evidence of alien life is 'unequivocal' on the comet carrying the Philae probe through space, two leading astronomers have said."

Wow. Unequivocal evidence of alien life. No doubts at all? Amazing.

But of course, this isn't the whole story, because there are a ton of doubts. Like the doubts expressed by the Rosetta mission scientists. Professor Monica Grady of the Open University, who helped design the Ptolemy instrument carried by Philae, states that the claims are anything but unequivocal. “I think it is highly unlikely,” Grady stated. Rosetta project scientist Dr Matt Taylor was also dismissive of the claims. “It's pure speculation. I think it is unlikely."

Now, of course, there is nothing wrong with acknowledging a number of opinions. The issue is that most articles aren't noting the dissent. Indeed, reading many of these articles, it seems that dissent doesn't exist, and the existence of alien life seems to be the consensus. It's not. This news shouldn't be too surprising.

Philae is currently resting comfortably on comet 67P/Churyumov–Gerasimenko, a 2.5-mile-wide (4-kilometer) comet that orbits around our solar system. And if you don't know, comets, by their very nature, are rather inhospitable places. First, they don't have an atmosphere in the traditional sense. This is notable because, on Earth, our atmosphere is what protects us from harm. For example, our atmosphere wards off harmful radiation from the sun.

It's true that, when comets get close to the sun, some of their ice starts to melt and boil off. This material then creates a kind of atmosphere, known as a coma; however, it's probably a bit more appropriate to think of comets as pots of boiling water. The material doesn't hang about in orbit around the comet; rather, it is blown off across the cosmos in a majestic tail.

Comet Pan-STARRS and tail, photographed by Phil Hart

Imagine if Earth's atmosphere acted like this. It would make for some pretty spectacularly bad times for life on our little planet.

Also, comets are cold. Very cold. In 2014, researches took the temperature of 67P, and they discovered that the average surface temperature is minus 94 degrees Fahrenheit (minus 70 degrees Celsius). And while research has shown that certain microorganisms can survive temperatures reaching minus 30 degrees Fahrenheit (minus 34 degrees Celsius), that is a bit warmer than the temperatures that we measured on 67P.

I could go on listing other reasons that life is unlikely, but I think the aforementioned serves to demonstrate the main point: Alien life on 67P is not unequivocal.

The Science Behind the Claims

Does the aforementioned (the lack of atmosphere and excessively cold temperatures) mean that alien life cannot exist on a comet? Of course not. There is, of course, some sound science behind the basic idea.

After a rather dramatic landing back in November, 2015, the small Philae lander went into a kind of hibernation, as it wasn't receiving enough sunlight in order to conduct operations; however, it woke up early in June. And thanks to the newly received data, some scientists are making some pretty amazing claims.

In essence, the claims all go back to a "black crust" that was seen on 67P. Astronomer and astrobiologist Professor Chandra Wickramasinghe thinks that this black material is evidence of the presence of living organisms beneath the comet's icy surface. This week, at the National Astronomy Meeting, Wickramasinghe and colleague Dr Max Wallis, from the University of Cardiff, argued that organisms containing anti-freeze salts could adapt to the conditions on 67P, asserting that some microbes could survive at temperatures as low as minus 40 degrees Fahrenheit (minus 40 degrees Celsius).

Wickramasinghe said that the black structure is a puzzle. "These are not easily explained in terms of pre-biotic chemistry," he stated. "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," and he continued,

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....Five hundred years ago it was a struggle to have people accept that the Earth was not the center of the universe. After that revolution our thinking has remained Earth-centered in relation to life and biology. It's deeply ingrained in our scientific culture and it will take a lot of evidence to kick it over.

In an email interview with From Quarks to Quasars, Wickramasinghe clarified these statements.

I think the evidence for biology on comet 67P is very strong, even though they are indirect. Eruptions of the comet occurred at distances from the sun too far away to trigger surface sublimation and be explained by inorganic processes. Indication is of sub-surface microbiology building pockets of high pressure gases that periodically crack overlying ice and vent organic particles including bacteria.

The dark surface of comet has a reflectivity spectrum matching biological material, and there is independent evidence of aromatic and aliphatic organics in great abundance. The comet shows a labile surface with a rugged terrain and evidence of fissures, re-sealed cracks, displaced boulders.

A surface covering of organics needs to be resupplied on a very short timescale, again indicating a biologically active comet. I think that microbial life exists in abundance throughout the galaxy - most of the 100 billion or so comets in our solar system will be full of microorganisms. Comets brought life to Earth 4 billion years ago, and continues to do so even today

It must be noted that it is not entirely conclusive that comets did, in fact, bring life to Earth, though it is a viable hypothesis. And I suppose this brings me to my main point. Sound science and interesting scientific hypotheses often get muddied by claims that sound absolute.

In relation to the most recent announcements and claims, as I have said before, in science, when something happens that is unexpected, or you discover something that you can't explain, you turn to the logical (and likely) conclusions first. You don't make "unequivocal" announcements without conclusive evidence. And if someone does do that, as a science reporter, you don’t just take the notion and run with it. Rather, you try and accurately articulate the likeliness of the claims.

Yes, you note that it is possible that the results are far, far more exciting than we anticipate, but we have a responsibility to note just how likely these results are and to try very hard to avoid exaggeration.

So. For today, there is no unequivocal evidence of life on any body except Earth, and according to several Rosetta scientists, there is no evidence of life on 67P at all. But maybe someday...

Note: This post has been updated to include additional commentary by Dr. Wickramasinghe.

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