Scientists Detected Potential Signs of Life on a Distant Planet. This Is Not a Drill.

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Scientists have announced the detection of dimethyl sulfide—a chemical that, on Earth, is only produced by living organisms—in the atmosphere of an exoplanet called K2-18b.
This is the second detection of the chemical by this team, the first having been made in 2023.
No one is shouting “aliens” yet—not by a long shot—but the detection is receiving widespread attention for its tantalizing potential.

There are so many stories about aliens circling the internet every day. From metal spherules to oblong ‘spaceships’ to flat-out hoaxes, somebody is crying E.T. pretty frequently.

But here’s the thing: if and when we do find alien life somewhere in our vast cosmos (and the odds are pretty good that it’s out there), it’s probably not going to take the form of a flying saucer or a little green man. Our first hint at life on another world is likely going to be a faint chemical signal that scientists just can’t explain away.

We saw this briefly with Venus a few years ago. A group of scientists detected odd pockets of phosphine in the upper atmosphere of the planet, which is only made in high quantities on Earth by life. Upon follow-up inspection, it turned out to probably be nothing. But that was the first “alien” ping that scientists had detected in a long time that was worth truly investigating.

Now, we might have another ping.

In a paper published in the Astrophysical Journal Letters, a team of scientists announced the detection of dimethyl sulfide (along with a similar detection of dimethyl disulfide) in the atmosphere of an exoplanet called K2-18b. This is actually the second detection of dimethyl sulfide made on this planet, following a tentative detection in 2023.

Tons of chemicals are detected in the atmospheres of celestial objects every day. But dimethyl sulfide is different, because on Earth, it’s only produced by living organisms.

“It is a shock to the system,” Nikku Madhusudhan, first author on the paper, told the New York Times. “We spent an enormous amount of time just trying to get rid of the signal.”

It may sound surprising that the scientists were “trying to get rid of the signal,” but that’s exactly how detections like this work. Pretty much all of the exoplanets we’ve ever seen are simply too far away to just … look at. Instead, to gather more information about what may lie on their surfaces, scientists observe the chemical makeups of their atmospheres.

This is done by capturing starlight that filters through those gaseous layers as a planet completes a transit in front of a host star. Different wavelengths of that starlight are blocked by different atmospheric chemicals, so by reading which wavelengths get filtered out as they pass through an exoplanets atmosphere, we can tell what that atmosphere is made of.

Astronomers have gotten very good at making these detections, but it’s still a difficult process. And the first step, every time, is to try and filter out noise—errant spikes in a spectrum that can disguise true detections—and false positives that might be caused by, say, a nearly invisible gas cloud in between us and an exoplanet.

So, when the astronomers spotted dimethyl sulfide in the atmosphere of K2-18b, they did everything to try to rule out the possibility that it was a ‘whoops.’

But even after carefully exhausting all the avenues they could think of over the course of two full observation sessions with JWST (which is rare in astronomy, considering how many teams want time with the coolest telescope we have) they found it impossible to attribute the detection to anything other than atmospheric composition.

And if you rule out the impossible, whatever remains—however improbable—must be the truth.

Now, it’s important to flag the fact that the “improbable” here is the fact that there is dimethyl sulfide in the atmosphere of K2-18b. It is not the presence of aliens. “Unless we see E.T. waving at us,” planetary scientist Christopher Glein told NYT, “it’s not going to be a smoking gun.”

But it is an exciting hint on a planet that we think may be ripe for alien life.

The current leading theory regarding the makeup of K2-18b is that it is what’s called a Hycean world. A combination of the words ‘hydrogen’ (describing the atmosphere) and ‘ocean’ (describing the surface), Hycean worlds are similar in size and density to Neptune, but covered entirely in one giant ocean of liquid water.

The existence of Hycean worlds has yet to be proven (again, we can’t see any of these worlds all that close up), but based on the evidence we do have at our disposal, the astronomical community thinks there’s a pretty solid chance they do.

If K2-18b is in fact a Hycean world, the strength of this dimethyl sulfide could indicate there’s life on an exotic ocean world—and that the ocean dominating that planet is absolutely teeming with, say, marine algae.

While algae isn’t little green men, the detection of any kind of life elsewhere in the cosmos would fundamentally change our understanding of our place in the universe.

According to the study, the detection sits at a confidence level of what scientists refer to as 3σ, meaning that there is about a 0.3 percent chance that this signal (even after all the filtering work the team did) is a fluke or background fluctuation, and not a real detection. In astrophysics, something is considered a discovery when the detection is made with a confidence level of 5σ, meaning that there is only about a 0.00006 percent chance the detection isn’t real.

At 3σ—especially regarding a claim as monumental as “we found a signal of alien life”—scientists (including the ones who made the discovery) are still proceeding with extreme caution; no one is saying, “this is aliens!” Astrobiologist Edward Schwieterman told NPR that the detection still seems “tentative” to him, and he wouldn’t be surprised “if the signal went away” when other researchers get their hands on the data collected by Madhusudhan and his team.

Even if the signal doesn’t go away, and the scientists get to do their second round of follow-up observations, and they get their confidence level up to 5σ, there’s still a chance it’s not a detection of life.

If we’re being honest, our data pool of planets that we even mostly understand contains just one point: Earth. There’s a solid chance that the chemistry on another world orbiting another star in another sector of our galaxy has managed to produce dimethyl sulfide without the need for life.

It’s going to take a preponderance of evidence for scientists to claim to have discovered extraterrestrial life, and on the path to doing so, they’re going to try to prove themselves wrong at every step (as they should). This detection is being made, as Schwieterman put it, “so close to the limits of our capabilities.” As a result, it will require a monumental pile of irrefutable proof to make any kind of claim about what a detection like this could mean. And even if—as is most likely—this detection turns out not to be a sign of life, it will be an incredible jump forward in our analysis and understanding of exoplanets and their atmospheres.

But, a two-time detection is not a “nothing” result. Sure, there’s still a chance that the signal turns out to have been an artifact of something else and goes away on further examination, but a provably replicable detection is definitely something worth presenting to the scientific community—and the world at large. Right now, everyone is holding their breath and waiting. No claims are being made, no proclamations are being shouted from the hilltops.

The possibility, however, is there in a way that it so rarely is.

As Madhusudhan told NPR, “when you are seeing something like this, it’s like—this is a question humanity has been asking for thousands of years, and if you’re witnessing it for the first time, it is a shock to the system. And it takes a while to recover from that, from the enormity of it.”

This is “potentially one of the biggest landmarks in the history of science,” he continued. “And I know this sounds grand, and it’s not my intention to make it sound grand, but there’s no other way to put it.”

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