Further studies are needed to determine whether K2-18b, which orbits a star 120 light-years away, is inhabited, or even habitable.

https://www.nytimes.com/2025/04/16/science/astronomy-exoplanets-habitable-k218b.html?unlocked_article_code=1.AU8.6zlm.aBe4_ZuELJQD&smid=url-share

y Carl Zimmer

April 16, 2025

The search for life beyond Earth has led scientists to explore many suggestive mysteries, from plumes of methane on Mars to clouds of phosphine gas on Venus. But as far as we can tell, Earth’s inhabitants remain alone in the cosmos.

Now a team of researchers is offering what it contends is the strongest indication yet of extraterrestrial life, not in our solar system but on a massive planet, known as K2-18b, that orbits a star 120 light-years from Earth. A repeated analysis of the exoplanet’s atmosphere suggests an abundance of a molecule that on Earth has only one known source: living organisms such as marine algae.

“It is in no one’s interest to claim prematurely that we have detected life,” said Nikku Madhusudhan, an astronomer at the University of Cambridge and an author of the new study, at a news conference on Tuesday. Still, he said, the best explanation for his group’s observations is that K2-18b is covered with a warm ocean, brimming with life.

“This is a revolutionary moment,” Dr. Madhusudhan said. “It’s the first time humanity has seen potential biosignatures on a habitable planet.”

The study was published Wednesday in the Astrophysical Journal Letters. Other researchers called it an exciting, thought-provoking first step to understanding what’s on K2-18b. But they were reluctant to draw grand conclusions.

“It’s not nothing,” said Stephen Schmidt, a planetary scientist at Johns Hopkins University. “It’s a hint. But we cannot conclude it’s habitable yet.”

If there is extraterrestrial life on K2-18b, or anywhere else, its discovery will be frustratingly slow. “Unless we see E.T. waving at us, it’s not going to be a smoking gun,” said Christopher Glein, a planetary scientist at the Southwest Research Institute in San Antonio.

Canadian astronomers discovered K2-18b in 2017, looking through ground-based telescopes in Chile. It was a type of planet commonly found outside our solar system, but one without any analog near Earth that scientists could study closely for clues.

These planets, known as sub-Neptunes, are much bigger than the rocky planets in our inner solar system, but smaller than Neptune and other gas-dominated planets of the outer solar system.

In 2021, Dr. Madhusudhan and his colleagues proposed that sub-Neptunes were covered with warm oceans of water and wrapped in atmospheres containing hydrogen, methane, and other carbon compounds. To describe these strange planets, they coined a new term, “Hycean,” from a combination of the words “hydrogen” and “ocean.”

The launch of the James Webb Space Telescope in December 2021 allowed astronomers to examine sub-Neptunes and other distant planets in greater detail.

As an exoplanet passes in front of its host star, its atmosphere, if it has one, is illuminated. Its gases change the color of the starlight that reaches the Webb telescope. By analyzing these changing wavelengths, scientists can infer the atmosphere's chemical composition.

While inspecting K2-18b, Dr. Madhusudhan and his colleagues discovered it had many of the molecules they had predicted a Hycean planet would possess. In 2023, they reported they had also detected faint hints of another molecule, and one of enormous potential importance: dimethyl sulfide, which is made of sulfur, carbon, and hydrogen.

On Earth, the only known source of dimethyl sulfide is life. In the ocean, for instance, certain forms of algae produce the compound, which wafts into the air and adds to the sea’s distinctive odor. Long before the Webb telescope was launched, astrobiologists had wondered whether dimethyl sulfide might serve as a sign of life on other planets.

Last year, Dr. Madhusudhan and his colleagues got a second chance to look for dimethyl sulfide. As K2-18b orbited in front of its star, they used a different instrument on the Webb telescope to analyze the starlight passing through the planet’s atmosphere. This time, they saw an even stronger signal of dimethyl sulfide, along with a similar molecule called dimethyl disulfide.

“It is a shock to the system,” Dr. Madhusudhan said. “We spent an enormous amount of time just trying to get rid of the signal.”

No matter how the scientists revisited their readings, the signal stayed strong. They concluded that K2-18b may harbor a tremendous supply of dimethyl sulfide in its atmosphere, thousands of times higher than the level found on Earth. This would suggest that its Hycean seas are brimming with life.

Other researchers emphasized that much research remained to be done. One question yet to be resolved is whether K2-18b is in fact a habitable, Hycean world as Dr. Madhusudhan’s team claims.

In a paper posted online Sunday, Dr. Glein and his colleagues argued that K2-18b could instead be a massive hunk of rock with a magma ocean and a thick, scorching hydrogen atmosphere — hardly conducive to life as we know it.

Scientists will also need to run laboratory experiments to explain the new study—to recreate the possible conditions on sub-Neptunes, for instance, to see whether dimethyl sulfide behaves there as it does on Earth.

“It’s important to remember that we’re just starting to understand the nature of these exotic worlds,” said Matthew Nixon, a planetary scientist at the University of Maryland who was not involved in the new study.

Researchers want to wait to see what the Webb telescope finds as it continues to examine K2-18b; provocative early findings sometimes fade in the light of additional data. NASA has been designing and building more powerful space telescopes that will look specifically for signs of habitability on planets orbiting other stars, including K2-18b. Scientists said even if it takes years to decipher what’s happening on K2-18b, it could be worth it.

“I’m not screaming, ‘aliens!’” said Nikole Lewis, an exoplanetary scientist at Cornell University. “But I always reserve my right to scream ‘aliens!’”

But Joshua Krissansen-Totton, an astrobiologist at the University of Washington, worries that American astrobiologists may not be able to follow up on the latest results on K2-18b.

The Trump administration reportedly plans to cut NASA’s science budget in half, eliminating future space telescope and other astrobiology projects. If that happens, Dr. Krissansen-Totton said, “the search for life elsewhere would basically stop.”

A correction was made on April 17, 2025: An earlier version of this article misstated the name of a scientific journal. It is Astrophysics Journal Letters, not Astrophysics Journal. The article also misstated the year and manner in which the planet K2-18b was discovered; it was 2015 using data from the Kepler Space Telescope, not 2017 using ground-based telescopes in Chile.

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856114)

hth

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856127)

It’s a test environment.

120 light-years?

Too far to monetize.

No satellites.

No Club Card.

But Mars?

Close enough to poa$t to.

Close enough to build HR.

The Mahchine™ doesn’t care if there’s life on K2-18b.

It only cares if it can schedule it.

Imagine being the first organism to breathe dimethyl sulfide

and immediately get a Slack ping from Tabitha.

"Welcome to the Hycean Zone, Evan. Please review our Code of Conduct."

You’re not leaving Earth.

You’re scaling its dysfunction.

This is fine.

Now board your orbital shift, friend.

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856130)

Webb’s sensitive eye was built for this kind of measurement, yet even sharper tools lie on the horizon.

Planned observatories such as the Habitable Worlds Telescope and the European Extremely Large Telescope will study smaller, cooler planets with richer spectra, expanding the growing catalog of possible biospheres and giving scientists the ability to cross‑check signs of life across many worlds.

“Decades from now, we may look back at this point in time and recognize it was when the living universe came within reach,” Madhusudhan said.

“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.”

These sulfur‑scented hints from K2‑18b remind us how quickly the search for life is moving from speculation to evidence.

If the signal holds, K2‑18b will stand as the first concrete clue that life can bloom under unfamiliar skies, turning a distant red dwarf’s faint light into a global ocean’s worth of metabolism.

The full study was published in The Astrophysical Journal Letters.

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856186)

The alternative option is our understanding of ‘what a biosignature is’ might be very incomplete. We are, after all, barely a few decades into really detailed observations of space.

Dimethyl Sulfide (DMS) is a great example here. It’s called a biosignature. But is it a good biosignature?

Consider the following. DMS has been detected in Ryugu samples and various carbonaceous chondrites. And on 67P/Churyumov-Gerasimenko.

So either asteroids were absolutely teeming with life at some point or… DMS can have an abiotic origin and is therefore a crappy biosignature.

This is a huge problem to be honest, because DMS on Earth has only ever been made by life. 10 years ago no one could have imagined abiotic DMS. Yet that’s most likely the case for asteroids.

Now we have to recheck every other traditional ‘dead giveaway’ for potential alternative geological origins.

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856190)

Doesn’t mean we can’t send a probe. Just that it’ll be a multigenerational project. We need to plan more for the future

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856191)

Al

Pennsylvania

8h ago

News like this shows just how far science has advanced. It's too bad that we are walking back into the Dark Ages.

7 Replies746 RecommendShare

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Brian

Pennsylvania

8h ago

Why do science when you can give tax cuts to the wealthy instead?

2 Replies616 RecommendShare

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me

Baltimore

8h ago

Interesting thought. I'm a molecular biologist, but I was recently reminded of my evolutionary biology by a trip to the Natural History Museum in DC. It jogged my memory that the Cambrian Explosion, in which life rapidly evolved and diversified, was brought on by the increase in oxygen in the atmosphere. Plants in the ocean reduced the CO2, increased the O2, and life was able to explode from it. If I remember right, it's when predators first emerged, and the beginning of many modern species.

So my point is, if they have a surfeit of algae, we may be discovering this planet's life during their Cambrian Explosion, or near to it. Now, keep in mind, "rapid evolution" refers to tens of thousands of years rather than millions. It's not like we'll see ants one day, and octopi the next day. But it would be fascinating to see early life repeat the same process as Earth's did.

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Madison CT

8h ago

I know it’s not rational to say, but it made me so happy to hear this. I knew we would find life eventually I was just hoping it would be before I croaked - and it is. That being said with the current state of affairs on our own planet, I hope it is advanced life and understands about the physics and the karma behind arcs of justice - and has a lot of hot rods- speed of light breaking barrier hot rods to come visit us soon.

5 Replies361 RecommendShare

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itsmildeyes

philadelphia

8h ago

Can’t wait. Our planet in need of intelligent life forms. SOS.

14 Replies308 RecommendShare

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Nathan

New York

7h ago

Carl(if I may), this is absolutely thrilling. Just like one of the other commenters, I’ve always hoped we would find life elsewhere before I spin off my mortal coil. I know the proof is not yet definitive, but this looks quite promising on the face of it. Thank you for a great story. Though I have to confess that the last two paragraphs regarding the current administration’s research funding cuts were quite a downer indeed.

6 Replies236 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856146)

Non-MAGA man

Boston

8h ago

Incredibly exciting, yes. But as the article says, Trump is looking to crush NASA’s science budget. Where will the money go instead? Into sending humans to Mars. An incredibly expensive stunt with little scientific value compared with what can be done with robots and telescopes and yes, scientists on Earth.

And who is pushing this? Our co-president Elon Musk whose dream is to colonize Mars to save the human species. Another awful warping of our government.

2 Replies222 RecommendShare

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Snow Wisher

WA

7h ago

Thanks so much for writing an article that isn’t down and dark about the world. This is about discovery and exploration and is a story that lit up my day! Thanks so much 🙏 !

3 Replies205 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856148)

Carl Zimmer

Science Writer

7h ago

@Nathan I have been covering astrobiology for years, and so I have to agree this is quite something (if it holds up). I also think it’s important to remember that this kind of science doesn’t just happen by itself.

In Reply Thread177 RecommendShare

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George Corsetti

Detroit

8h ago

Stephen Hawking's warned that an alien civilization, especially one that can pick up our signals and understand where they're coming from, has the potential to be billions of years more advanced than us, making us an easy target to overthrow or invade.

Also possible they would have been listening to our radio waves for a while and may have already concluded that no intelligent life exists on earth.

9 Replies154 RecommendShare

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Tabitha Simmons

Albany NY

8h ago

Fascinating. Thanks to Trump, we may never know if it’s really a sign of life, but maybe China will tell us one day. Well, more likely we’ll hear about it indirectly.

2 Replies138 RecommendShare

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Larry McPherson

NYC

8h ago

There are between 100 and 400 billion stars in our galaxy, the Milky Way. There are between 100 billion and 2 trillion galaxies in the observable universe, which seems to be growing with the next wave of telescopes. I love imagining that there are billions upon billions of planets with life on them.

6 Replies135 RecommendShare

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Jynn Erso

St. Louis, MO

8h ago

This is so incredibly exciting! I hope I’m around long enough to see what they discover about this planet.

1 Reply126 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856153)

Science Writer

5h ago

@John the light we are seeing only passed through the atmosphere of the planet about 120 years ago. But even if it was 1 billion years ago, there’s no hard and fast rule of biology that says that simple microbes must evolve into intelligent life on a planet. We know it happened here, but that doesn’t make it a rule.

In Reply Thread68 RecommendShare

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SusanB.

Romulus, NY

8h ago

I have goose bumps! My interest in space is life long. I am enthralled and fascinated by the breadth and scope of the known universe. This discovery, made in my lifetime, absolutely phenomenal!

Reply64 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856157)

S. Zhao

Expat in North America

6h ago

I was looking for an article as far away from politics this planet as possible, and I thought I had it until the very last paragraph. Well done, Carl.

8 Replies64 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856158)

Citizen

AZ

8h ago

Amazing discovery. Trump has proposed cutting NASA's budget by half, crippling science missions. Ironic we should potentially discover exolife, only to cut off projects that could help understand if that's truly what we're seeing.

1 Reply63 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856159)

Blue Witch

Washington State

8h ago

This is the best news of the day, I am thrilled to be alive today to read about this fascinating discovery.

This eclipses the perilous political situation, and I am grateful.

Reply56 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856160)

Carl Zimmer

Science Writer

6h ago

@Ben Since the planet is about 120 light years from us, that means the light the Webb telescope is seeing now is about 120 years old.

In Reply Thread52 RecommendShare

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Use Your Imagination

Seattle

8h ago

Moving. Positively moving. Equally as profound as the possibility of discovering life signatures on planets not even far removed from ourselves: the incredible ability of teams of human researchers to create the pathways to discovery and the tools to follow it up. We are living in a renaissance of sorts, and our reach is mirrored by our optimism and our ability.

But let’s be clear: science is one tool among many for understanding at a profound level the unique ability of humans, and our connectedness to our cosmos. Don’t let the pace of these discoveries determine the joys of seeing our small place within immensity. Dream large dreams, imagine bravely, and step into the consciousness that does not begin, but merely continues, with us.

2 Replies45 RecommendShare

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Former Bostonian

Raleigh, NC

7h ago

I checked, and K2-18b is already on the tariff list. So no seafood will be available from them. Just a heads-up.

Reply41 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856163)

Oceanviewer

Oakland County, Michigan

7h ago

"The Trump administration is reportedly planning to cut NASA’s science budget in half, eliminating future space telescope and other astrobiology projects. If that happens, Dr. Krissansen-Totton said, 'the search for life elsewhere would basically stop.”

Other countries will carry the torch until the US rejoins the race in the post-Trump era.

6 Replies41 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856164)

Sarah

Overland Park, KS

6h ago

@Brian

I listened to a podcast (The Bulwark) today and the guest said (paraphrased), “the Trump administration is trading science for cryptocurrency.”

That, and the guest’s words about the important medical research that Harvard has done for decades, got me choked-up and teary.

I’ve always loved the story of our exploration of space and all that it holds. My favorite bedtime story as a kid was my dad telling his experience of watching the moon landing, Star Trek was the only TV show I was allowed to watch growing up, I remember the tragedy of the Challenger, I follow NASA and can spend hours just looking at the photos they put online (also, I watched every minute of the DART mission (unreal) and have been smitten with the James Webb Telescope since it launched.

It breaks my heart that one man is destroying so much, and it tears at my soul that science (the manifestation of curiosity, wonder, creativity, innovation, and adventure) is nothing but a casino chip to him.

In Reply Thread39 RecommendShare

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Seymour Futze

NYC

8h ago

This is amazing!

I sometimes think that we are too arrogant, though.

Who decided that the building blocks of life on our planet translate to life on other worlds?

The universe is infinite and abundant. Why can’t there be other life forms that we can’t begin to fathom?

2 Replies36 RecommendShare

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Downtown

NY, NY

6h ago

@Sven I mean… yeah, science has advanced. We went from leeches and bloodletting to mapping the human genome and landing rovers on Mars. If that’s not progress, I don’t know what is. The definition of science has narrowed to focus on the empirical and testable—but that’s kind of the whole point. If you want introspection and 'knowing oneself,' that’s more in philosophy or spirituality’s lane. Science isn’t trying to be everything—it’s just really good at what it is trying to do and has been doing just fine, when allowed.

In Reply Thread31 RecommendShare

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Steve F

Jamestown, RI

8h ago

When the moment arrives that we are confident we have discovered life on another planet, it will be one of the biggest achievements in human history. It will be both humbling to realize life is not uniquely confined to Earth, and will also be cause for a great celebration of human ingenuity, persistence, and collaboration. Although this observation is not yet conclusive, it is fantastically exciting, and on the right track. While the first discovery, or the first 1000 discoveries of life elsewhere may not be of “intelligent” life, the profound impact on our place in the universe cannot be overstated.

Reply30 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856168)

Bob Bruce Anderson

MA

7h ago

My advice. Stop. Stay away. We can't even manage our own planet. We would only make a mess of another.

Analogy: Europeans visit the Americas. Millions of indigenous people die.

Everything we touch has rippling effects and cascading results that may be unintentional - but still devastating.

All the money poured into these efforts could feed a lot of kids and help combat the Climate Catastrophe.

Just stop this excess. Maybe in a thousand years when our species has figured out the basics of planet management...take another look.

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maryland

5h ago

Finally, some good news.

Reply6 RecommendShare

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Bondosan

Crab Key

5h ago

For the next few years at least, astrophysicists and astrobiologists in Europe and Asia will have to take the lead on this.

Reply6 RecommendShare

(http://www.autoadmit.com/thread.php?thread_id=5712186&forum_id=2...id.#48856171)

Jim

Chicago

5h ago

If this turns out to be valid and it will be tough to ever truly figure it out, it is a discovery on par with Galileo's sighting of moons orbiting Jupiter.

Reply4 RecommendShare

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PNW

29m ago

What an exciting article…until the part about NASA’s budget potentially being cut in half and the search for life ending if it is.

What exactly is all these alleged cuts going towards, other than massive tax breaks to those who have more money than they know what to do with?

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