Astronomers Find Most Promising Signs of Alien Life Ever Detected

Since before recorded history, humanity has looked up at the stars and wondered if we’re alone in the universe. Now, astronomers may be on the brink of finding out for sure.

To date, more than 5,000 exoplanets have been discovered throughout the cosmos, but so far none of them have shown any telltale signs of being inhabited. No matter where we look, we haven’t found any hint of Harry Vanderspeigle (or any of the extraterrestrials from Resident Alien, for that matter). Well, except on one exoplanet, where astronomers have now found the most promising signs of alien life ever detected.

Exoplanet K2-18b keeps teasing signs of alien Life 120 light-years away

In 2015, astronomers discovered the planet K2-18b orbiting a red dwarf star about 120 light-years from here. The planet orbits its star edge-on from our perspective, so once per orbit it passes directly in front of its star and we can see it. K2-18b orbits its star once every 33 days at a distance of about 14 million miles.

That’s much closer than Earth’s 93-million-mile orbit, but red dwarfs are dimmer. In the end, K2-18b gets about the same amount of starlight as Earth does, putting it in the system’s habitable zone.

As astronomer Phil Plait wrote at the time, “if you’re searching for worlds with potential for life, K2-18b isn’t a bad place to keep in mind.”

Based on initial observations, astronomers estimated K2-18b was about 2.5 times the diameter of Earth and about 8 times the mass, with a surface gravity 1.5 times that of Earth. Those observations also suggested the possibility of liquid water or ice on the surface, and an atmosphere. Then, in 2023 astronomers detected tentative biosignatures on K2-18b.

Observations using JWST’s onboard instruments suggested a Hycean planet, a world containing liquid water or ice and a hydrogen-rich atmosphere. They also revealed more detailed information about the planet’s atmosphere.

Imagine you wanted to find out what animals existed in an animal preserve, but you weren’t allowed to go there. Instead, plates filled with every kind of food were passed through the preserve and you were allowed to look at the remnants. If the plates make it through unscathed, you might conclude the preserve is empty. If, instead, everything gets through except the zebra meat, you can be pretty confident there are lions in there. That’s how spectroscopy works.

Astronomers look at the light coming from a star before, during, and after a planetary transit. When the planet isn’t in front of the star, the starlight (plates) get to us untouched. When the planet transits, however, some of the light frequencies get absorbed by molecules in a planet’s atmosphere. When astronomers look at the starlight then, there are gaps in the spectrum (food missing from the plates) and they can tell what the atmosphere contains.

Spectral data from 2023 revealed methane and carbon dioxide in K2-18b’s atmosphere, alongside a weak and tentative detection of dimethyl sulfide (DMS).

Astronomers have detected most promising signs of alien life ever on Exoplanet K2-18b

On Earth, DMS is produced exclusively by living organisms, mostly phytoplankton and some bacteria. It’s a major component of the “fishy smell” you encounter anytime you’re at the beach. At the time, astronomers noted that the DMS detection was tantalizing, but tentative.

In May 2024, an additional study cast some doubt on the data, suggesting that in order for DMS to be detectable by existing instruments, it would need to exist at concentrations at least 20 times higher than on Earth. Ultimately, astronomers everywhere agreed more data was needed. Now, more data has arrived.

Researchers from the Institute of Astronomy at the University of Cambridge recently announced additional evidence for the detection of DMS and other life-associated molecules on K2-18b. The results, being hailed as the most promising signs of alien life ever discovered, were published in The Astrophysical Journal Letters.

Recent observations using an entirely different instrument detected either DMS, as the previous observations had, the related molecule dimethyl disulfide (DMDS), or some combination of the two. In any case, on Earth those molecules are only made by life. Of course, extraordinary claims require extraordinary evidence, and even the researchers involved with the study reiterate that they aren’t yet totally confident life exists on K2-18b.

“It’s important that we’re deeply skeptical of our own results, because it’s only by testing and testing again that we will be able to reach the point where we’re confident in them,” Professor Nikku Madhusudhan from Cambridge’s Institute of Astronomy said in a press release. “That’s how science has to work.”

The next steps will be to confirm the detection at an even higher degree of confidence. Once we’re sure there’s DMS and/or DMDS in the atmosphere of K2-18b, then we have to figure out if they can be formed through ordinary (non-living) chemistry. They also note that if the signal is confirmed, then DMS/DMDS exists at levels thousands of times higher than on Earth.

Scientists hypothesize that a planet covered in a global ocean and filled with something like phytoplankton could produce the detected signal. Then again, additional observations might reveal some other explanation or even cause the signal to vanish.

K2-18b may or may not be the place we first find alien life off Earth, but it highlights a new frontier in astronomy unlocked by cutting edge observatories and tools. If life is out there, on K2-18b or anyplace else, we’re better equipped to find it than ever before.

“Decades from now, we may look back at this point in time and recognize it was when the living universe came within reach,” said Madhusudhan. “This could be the tipping point, where suddenly the fundamental question of whether we’re alone in the universe is one we’re capable of answering.”

While you’re waiting for answers, catch up on all three seasons of Resident Alien, streaming now on Peacock.