Scientists Might Have Detected Strongest Hints of Life on Distant Planet

Scientists Might Have Detected Strongest Hints of Life on Distant Planet

Astronomers have identified potential signs of life on K2-18b, a distant exoplanet 124 light-years away, using the James Webb Space Telescope (JWST).

The discovery centers on detecting dimethyl sulfide (DMS) and possibly dimethyl disulfide (DMDS) in its atmosphere—compounds on Earth primarily produced by marine phytoplankton and bacteria.

Nikku Madhusudhan, professor of astrophysics and exoplanetary science at the University of Cambridge’s Institute of Astronomy, and his colleagues believe K2-18b, located 124 light-years from Earth, is a Hycean world, or a potentially habitable planet entirely covered in liquid water with a hydrogen-rich atmosphere.

“Given everything we know about this planet, a Hycean world with an ocean that is teeming with life is the scenario that best fits the data we have,” he said.

However, the study authors have not declared a definitive discovery of life beyond our planet — and experts remain skeptical about the idea of the molecules representing signs of biological activity.

The term “Hycean planet” is relatively new, coming out in 2021, and means an exoplanet with a hydrogen-rich world with a global liquid water ocean. Other exoplanet categories include “Rocky” (like Earth), “Super Earth” (a rocket with water 2 to 10 times larger than Earth), sub/mini-Neptune (rocky core with a gaseous envelope), “Gas Giants” (all gas and quite large, like our system’s Jupiter), “Ice Giant” (Gas Giant, but with frozen has core, like Uranus).

This classification, proposed by the Cambridge-led team in 2021, seems to be confirmed with K2-18b’s position in its star’s habitable zone and atmospheric composition.

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 a closer look at sub-Neptunes and other distant planets.

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 chemical composition of the atmosphere.

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 huge potential importance: dimethyl sulfide, which is made of sulfur, carbon, and hydrogen.

Our @NASAWebb telescope detected carbon dioxide and methane in the atmosphere of a planet orbiting a faraway sun. The planet might have an ocean, but more observations are needed to determine whether it could support life: https://t.co/J8ub8PqwMG pic.twitter.com/SbgHjOO9Hv

— NASA (@NASA) September 11, 2023

Many astronomers assert it is wise to be skeptical, especially as the gas signatures appear at the limits of instrument detection.

Astronomers not involved in the research have additionally expressed some skepticism about the study’s conclusions. “I think this is one of those situations where extraordinary claims require extraordinary evidence,” says Laura Kreidberg, an astronomer at the Max Planck Institute for Astronomy who was not part of the research team, to Nell Greenfieldboyce at NPR. “I’m not sure we’re at the extraordinary evidence level yet.”

“It’s not nothing,” adds Stephen Schmidt, a planetary scientist at Johns Hopkins University who did not participate in the study, to Carl Zimmer at the New York Times. “It’s a hint. But we cannot conclude it’s habitable yet.”

The molecules detected by Webb could also be produced without the presence of life, such as in comets, explains astrophysicist Jake Taylor to Astha Rajvanshi at NBC News. “I do not believe this is the biosignature detection that will revolutionize astronomy,” he adds. But it’s “a good first step.”

As a geologist and a historian, I have one quibble with the depictions of K2-18b that I have seen. There are suggestions that Earth’s waters may have been green when life began on this planet over 3.7 billion years ago.

Photosynthetic organisms use pigments (mostly chlorophyll) in their cells to transform CO₂ into sugars using the energy of the sun. Chlorophyll gives plants their green color. Blue-green algae are peculiar because they carry the common chlorophyll pigment, but also a second pigment called phycoerythrobilin (PEB).

In their paper, the researchers found that genetically engineered modern blue-green algae with PEB grow better in green waters. Although chlorophyll is great for photosynthesis in the spectra of light visible to us, PEB seems to be superior in green-light conditions.

Before the rise of photosynthesis and oxygen, Earth’s oceans contained dissolved reduced iron (iron deposited in the absence of oxygen). Oxygen released by the rise of photosynthesis in the Archean eon then led to oxidized iron in seawater. The paper’s computer simulations also found oxygen released by early photosynthesis led to a high enough concentration of oxidized iron particles to turn the surface water green.

Once all iron in the ocean was oxidized, free oxygen (0₂) existed in Earth’s oceans and atmosphere. So a major implication of the study is that pale-green dot worlds viewed from space are good candidate planets to harbour early photosynthetic life.

Furthermore, the high concentration of dissolved iron, especially as triple-charged iron (Fe(III)), interacted with sunlight in a way that made the oceans appear green.

My alternative proposal for what exoplanet K2-18b would look like. pic.twitter.com/cO7Kh497A1

— Leslie Eastman ☥ (@Mutnodjmet) April 22, 2025

More good news: The planet’s aliens will not likely target us after discovery.

Their gravity well is prohibitive. K2-18b is an ocean. Any life there is going to be aquatic.

These parameters give good odds against them developing any kind of space travel. They are trapped on their planet. Likely ignorant of other worlds.

We have the advantage. 🤜💥👽 pic.twitter.com/CYFiWhfNwq

— Benjamin Prime (@Mr_BenPrime) April 17, 2025

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