Alien Poop Means We Are Not Alone. But Let Me Just Adjust This Model Parameter...

K2-18b and our new age of alien agnosticism

Art for The Intrinsic Perspective is by Alexander Naughton

There’s now smelly scientific evidence for alien life on other worlds. We think. Probably. Maybe. Coin toss? 40%? Come on, it’s gotta be at least 30%.

Welcome to my predicted age of “alien agnosticism,” wherein belief in alien life—based on modern space telescopes detecting, light years away, biological and even technological signatures—is not exactly justified scientifically, but it’s also not unjustified either.

For example, on Wednesday we were treated to a pretty incredible headline:

source

If anything, The New York Times (and other outlets) downplayed the news. As a new paper published in The Astrophysical Journal Letters shows, this distant planet, K2-18b, contains in its atmosphere a chemical, dimethyl sulfide, which only gets produced in relevant quantities from life (as far as we know). But when giving the skeptical “maybe this isn’t true” side in the Times article, renowned science reporter Carl Zimmer referenced a different paper arguing K2-18b has a huge magma ocean and therefore couldn’t be habitable. On closer examination, that paper has zero mention of dimethyl sulfide, and so can’t possibly explain the new observation. In fact, it doesn’t even reference the new results!

If you accept the latest evidence at face value, alien life is now arguably the leading hypothesis. And K2-18b joins an ever-growing list of suggestive biosignatures on multiple exoplanets. There’s TOI-270d, sporting not only methane but also carbon disulfide (which on Earth mostly comes from biological processes), along with signs of an out-of-equilibrium atmosphere implying weird conditions we don’t understand… or life. There’s TRAPPIST-1e, another world which will soon be subject to James Webb Space Telescope observations with clear prior predictions about biosignatures from modeling. Even Proxima Centauri b—literally the closest exoplanet to Earth—could possibly have an oxygen atmosphere (which isn’t unique to life, but is suggestive), and at some point in the near future studies will examine its surface reflectance, since any vegetation will leave behind a detectable signature there.

There are now even possible technosignatures of alien life, not just biosignatures. As I’ve written about, researchers have quietly identified 53 stars that are Dyson sphere candidates, detected via excess mid-infrared emissions. They’re just candidates requiring investigation, of course, but the search for Dyson spheres is now firmly in the realm of real science, not fiction. Then there’s ʻOumuamua: noticed back in 2017, it was the first identified interstellar object to wander through our solar system, and was also weird in almost every way, from its thin oblong shape to how it accelerated away. I don’t judge all of this as equally good evidence (ʻOumuamua has multiple natural explanations), but collectively the growing list of biosignatures and technosignatures represents a major change. Alien life is no longer about waiting for evidence, but debating the surprisingly not-crazy evidence we do have.

It’s ironic this comes during a time of UFO rumors and sightings of lights in the sky. Personally, I discount all that entirely. The New Jersey Drones? A mass hysteria from hobbyist flights. Even the newly established official AARO, a government program supposed to investigate UFO sightings by pilots, is a bit of a farce, for its creation was built on a lie. Basically, back in 2008, a group of paranormal believers hunted for things like “dino-beavers” (really) on Skinwalker Ranch, using money from a government grant received via (ahem, what seems like) nepotism. Their chasing of ghosts and goblins, in turn, got misreported by The New York Times as being a super-secret government search for UFOs. The misreporting by the Times triggered a public outcry, so the AARO was created to investigate, and since then has delivered null results. All the major pilot sightings of mysterious UFOs have been debunked as cases of parallax, not understanding how the tracking systems automatically adjust, or literally just blurry far-away planes.

Yet as everyone has been distracted by all the fake UFO news, the actual scientific effort to find alien life has kept chugging along. The telescopes have gotten better. The data sets are bigger. More importantly, the social stigma is gone: scientists regularly write serious papers proposing candidates. This dry academic stuff is real. Meaning that the new data from K2-18b is the best evidence there’s been, ever, to indicate alien life—even if it’s still an uncertainty.

While the K2-18b news got its share of commentary on social media, it was less than one might expect. When “Are we alone in the universe?” gets answered in sci-fi movies and books, it usually entails ontological shock. In reality, we’re in for a long and drawn-out scientific debate over models with tons of parameters. Meaning you must personally choose when to believe in aliens.

Consider the story of K2-18b, which goes back years (indeed, I’ve written about K2-18b before here on TIP). It was first discovered in 2015, ~120 light-years away, sitting in the not-too-hot, not-too-cold Goldilocks zone of its star where water can be liquid. It joined the list of exoplanets (planets we’ve identified around other stars) that exist in a similar habitable zone (the zone depends on the type of star).

The Goldilocks zone visualized, with various exoplanets, along with planets from our own solar system too (source)

Then, in 2023, Nikku Madhusudhan at the University of Cambridge (and his co-authors) presented evidence that K2-18b might be a “hycean world”—a water world, covered entirely in ocean, with atmosphere unlike our own, in that it contains primarily hydrogen. This was based on spectroscopy observations from when the planet passed in front of its star (planetary transit), at which point scientists can use tools like the James Webb Space Telescope to analyze its conditions based on how the star’s light moves through the atmosphere. Importantly, the team reported finding methane: a classic biosignature, since most methane on Earth is produced by life (a lot of it from animals farting, basically). But there are also abiotic sources of methane, like volcanoes. So, far more importantly, they also reported detecting dimethyl sulfide. And dimethyl sulfide is a lot harder to produce via abiotic means. Ever cook cabbage? You’ve smelled dimethyl sulfide. It’s also created in vast quantities by phytoplankton. That fishy-odor you’ve whiffed at the beach? Dimethyl sulfide. Pigs sniff out truffles via dimethyl sulfide, and so too the James Webb Space Telescope sniffed out dimethyl sulfide on K2-18b. As my wife aptly put it: “It’s like we found someone’s poop.”

However, that original detection back in 2023 was statistically tenuous. When other researchers looked at the data, the finding of dimethyl sulfide wasn’t statistically significant. Okay, no life. Yet now we have a new paper from Madhusudhan et al. (what all the outlets are reporting on) with better data, making a clearer claim for a signal of dimethyl sulfide. Okay, life! But wait. Just in January, dimethyl sulfide was identified in a comet. So dimethyl sulfide can have an abiotic origin. So no life! But that was in small quantities, and there’s no way comets could deliver enough to explain the readings. What about other abiotic means? Dimethyl sulfide has been produced in labs via purely chemical processes, but it decays quickly in the conditions we know about. So as of right now, there’s no plausible way to get dimethyl sulfide via abiotic means in the high quantities seen on K2-18b. So life?

Unsure? Get used to it. There may be no observational data that’s 100% a sign of life, with zero possible false positives. Observations will have to be followed by modeling and then, eventually, experiments. If dimethyl sulfide degrades quickly here, in our nitrogen-rich atmosphere, what about in an atmosphere more like on K2-18b? That’s a major experiment waiting to happen. But the conclusion will always be sensitive to someone coming up with an ingenious, never-before-seen process by which the biosignature could actually be abiotic in origin.

I don’t know how long this period of alien agnosticism will last, but I do know it’s officially begun. It reflects a broader symptom of our age: as our world ever more resembles science fiction, we become collectively more uncertain, not less. A counterintuitive effect. I think it’s because public life is increasing in contact with the full surface area of science, and a lot of science’s surface area is not back in its bow wave of settled science, where there’s capital-T Truth. Much of the area is unsettled frontier. And as the frontier of science increasingly abuts public culture and consciousness, so too does the agnosticism inherent to the frontier settle like a thick mist upon subjects that would have seemed, historically, to require demarcations and answers. E.g., we now have AI models that are very smart. Yet they still mess up simple stuff and lie and hallucinate. Benchmarks get saturated, and nowadays only experts or the eagle-eyed can detect the latest model’s mistakes. Somehow, AI’s impact on GDP is also basically non-existent. All very strange. When do we declare AGI achieved? No one knows.

The public has been thrust into working science. And working science entails a mode of existence less like “I’m right about everything” and more like “I’m surrounded by contradictory publications.” Now everyone gets to share in this special experience. Welcome to the frontier of knowledge—which is really more like a cliff of confusion. It’s windy here, and the dust gets in your eyes; but, in the rare cases when the weather clears, the vistas sure are beautiful.

So if you want to believe in aliens, this week is probably the best time to believe that so far in human history. That’s the thing about our new age of agnosticism. Everyone makes their own choice.

Religiously, I’ve been a self-declared agnostic for years, and a common misconception is that agnostics exist in a state of uncertainty all the time. The human mind isn’t capable of that. Rather, it means on some days, I believe. On others, I don’t. So too over the last few years has waxed and waned my faith about whether there’s life on K2-18b, and if this universe of ours is really filled with vital force and grand dramas beyond sight.

Today, I want to believe.