Scientists Uncover Most Compelling Evidence of Life on a Distant Exoplanet

In what could be a monumental stride in humanity’s quest to find life beyond our solar system, astronomers have identified the strongest biosignatures yet on an alien world.

Utilizing the James Webb Space Telescope (JWST), scientists observed the exoplanet K2-18 b and detected atmospheric traces of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS)—gases that, on Earth, are produced only by living organisms, mainly marine phytoplankton.

Researchers assert that this finding offers a significant clue in the ongoing search for extraterrestrial microbial life. However, they emphasized the need for caution, stating that the detection represents a biosignature, not definitive proof of living organisms.

Cautious Optimism Amid a Major Milestone

“These are the first hints of an alien world that is possibly inhabited,”
— Nikku Madhusudhan, University of Cambridge Institute of Astronomy

Dr. Nikku Madhusudhan, lead author of the study published in Astrophysical Journal Letters, described the breakthrough as a "transformational moment" in the field of astrobiology.

“This is a transformational moment in the search for life beyond the solar system, where we have demonstrated that it is possible to detect biosignatures in potentially habitable planets with current facilities. We have entered the era of observational astrobiology.”

What Makes K2-18 b a Candidate for Life?

A Hycean World in the Habitable Zone

K2-18 b, located about 124 light-years from Earth in the constellation Leo, is approximately 8.6 times more massive than Earth and has a diameter 2.6 times larger. The planet orbits within the habitable zone of a red dwarf star, a region where liquid water—a critical ingredient for life—can exist.

The exoplanet belongs to the "sub-Neptune" class, sitting between Earth and Neptune in size. Scientists have long theorized the possibility of hycean worlds—ocean-covered planets with hydrogen-rich atmospheres capable of supporting microbial life.

“The only scenario that currently explains all the data obtained so far from JWST (James Webb Space Telescope), including the past and present observations, is one where K2-18 b is a hycean world teeming with life,” Madhusudhan said.

“However, we need to be open and continue exploring other scenarios.”

Life in Alien Oceans?

Madhusudhan notes that if such hycean worlds exist, they may host microbial life similar to marine microbes on Earth, potentially thriving in warmer oceans. When asked about more complex organisms or intelligent life, he clarified:

“We won’t be able to answer this question at this stage. The baseline assumption is of simple microbial life.”

The Role of DMS and DMDS as Biosignatures

Gases Uniquely Linked to Life on Earth

DMS and DMDS are both biologically produced gases from the same chemical family. These molecules are rarely found without life-related processes. Webb’s observation detected them in K2-18 b’s atmosphere with a 99.7% confidence level, though that leaves a 0.3% possibility of a statistical anomaly.

“For reference, this is thousands of times higher than their concentrations in the Earth’s atmosphere, and cannot be explained without biological activity based on existing knowledge,” Madhusudhan said.

How the Discovery Was Made Using the Transit Method

Capturing Planetary Light with the James Webb Telescope

The discovery hinged on the transit method, where Webb observes the light from a star as a planet crosses in front of it from Earth's perspective. During the transit, starlight passes through the planet’s atmosphere, allowing scientists to analyze the chemical makeup via subtle changes in light.

Earlier observations using Webb had revealed carbon-based molecules such as methane and carbon dioxide in K2-18 b's atmosphere—another first for a planet within a habitable zone.

The new detection of DMS/DMDS utilized a different instrument and light wavelength, providing a much stronger signal than before.

Scientific Community Reacts with Cautious Enthusiasm

Calls for Peer Review and Further Validation

Experts not involved in the study have praised the findings but urged scientific restraint.

“The rich data from K2-18 b make it a tantalizing world,” said Christopher Glein, principal scientist at the Space Science Division of the Southwest Research Institute in Texas.
“These latest data are a valuable contribution to our understanding. Yet, we must be very careful to test the data as thoroughly as possible.”

What Comes Next in the Search for Life?

Repeat Observations and Alternate Theories Needed

While the results are promising, Madhusudhan underscored the importance of verification:

“First we need to repeat the observations two to three times to make sure the signal we are seeing is robust and to increase the detection significance to the level at which the odds of a statistical fluke are below roughly one in a million.”

He also stressed the need to explore non-biological (abiotic) explanations:

“Second, we need more theoretical and experimental studies to make sure whether or not there is another abiotic mechanism (one not involving biological processes) to make DMS or DMDS in a planetary atmosphere like that of K2-18 b.”

“Even though previous studies have suggested them (as) robust biosignatures even for K2-18 b, we need to remain open and pursue other possibilities.”

Are We Alone? The Search Continues

While the findings fall short of confirming alien life, they do mark a historic milestone in our journey to answer one of humanity’s most enduring questions: Are we alone in the universe?

“It is in no one’s interest to claim prematurely that we have detected life,” Madhusudhan concluded, highlighting the scientific integrity behind the discovery.