Did Spectroscopy Help Find Signs Of Life 124 Light Years Away?

By John Oncea, Editor

Using advanced spectroscopy, JWST detected potential biosignature gases in K2-18b’s atmosphere, sparking debate about life beyond Earth.

What’s bigger than Earth, smaller than Neptune, might have conditions that allow for liquid water, and is unlike anything in our Solar System? K2-18b, a planet that could just as likely be covered in magma as it is in water, which exists 124 light years away.

It was recently announced that scientists may have detected a chemical almost uniquely associated with life on Earth — dimethyl sulfide — in K2-18b’s atmosphere. “If the evidence holds up,” writes The Planetary Society, “this would mean that a world more than 100 light-years away hosts a substance that, on Earth, only exists because of plants and microbes.”

In other words, signs of life.

The announcement has caused an uproar in astronomy circles, with some scientists questioning whether the data is strong enough to support the claim of finding alien life. In fact, NPR reports, “The detection of these gases needs to be confirmed with more telescope observations. And other astronomers are skeptical.”

“I think this is one of those situations where extraordinary claims require extraordinary evidence,” Laura Kreidberg, an astronomer at the Max Planck Institute for Astronomy in Germany who did not play a role in the research effort, said. “I'm not sure we're at the extraordinary evidence level yet.”

The discovery of life anywhere in the Universe – even something as simple as space phytoplankton – would be big if true. But we’re going to wait until astronomers have had time to independently analyze the publicly available data because, as Måns Holmberg, a researcher at the Space Telescope Science Institute who was part of the group announcing the findings, said, “For looking at things like this, it requires a dedicated community effort.”

What we can do now, however, is dig a little deeper into the role spectroscopy played in sniffing out dimethyl sulfide (DMS), the chemical that is causing the uproar, in quantities 20 times higher than on Earth.

Discovering K2-18b

K2-18b, an exoplanet orbiting the red dwarf K2-18, was discovered in 2015 by NASA’s Kepler mission, which revealed that planets outside our solar system are so common that they outnumber stars.

“Launched on March 6, 2009, the Kepler space telescope combined cutting-edge techniques in measuring stellar brightness with the largest digital camera outfitted for outer space observations at that time,” writes NASA. “Originally positioned to stare continuously at 150,000 stars in one star-studded patch of the sky in the constellation Cygnus, it took the first survey of planets in our galaxy and became the agency's first mission to detect Earth-size planets in the habitable zones of their stars.”

Playing a part in the way Kepler discovered planets such as K2-18b was the observation of transits, tiny dips in a star’s brightness caused by a planet crossing in front of it that briefly blocks a small amount of light, creating a noticeable dip in the star’s light curve.

To accomplish this, Kepler uses several concepts, including photometry, a method of measuring light intensity that can be applied to monitoring the brightness of thousands of stars simultaneously, according to the National Institute of Standards and Technology.

Kepler’s data, which measures brightness over time, creates a light curve for each star. A transit, where a planet crosses in front of a star, appears as a dip in the light curve. Kepler uses 42 Charge-Coupled Device (CCD) detectors, similar to those in digital cameras, to collect and measure the light from the stars. By analyzing the depth, duration, and periodicity of the transit, scientists can determine the size, orbital period, and other properties of the planet. 

How K2-18b’s Chemical Signature Was Spotted

In the search for extraterrestrial life, the exoplanet K2-18b has become a focal point for astronomers. Located about 124 light-years from Earth in the constellation Leo, K2-18b is a “Hycean” world type of planet theorized to have a hydrogen-rich atmosphere and a possible water ocean beneath, writes SciTechDaily. The discovery of potential biosignature gases in its atmosphere has reignited debates about the prospects for life beyond our solar system.

The breakthrough came from observations made by the James Webb Space Telescope (JWST), which has revolutionized exoplanetary science with its cutting-edge photonic instruments. The telescope employs transmission spectroscopy, a technique that examines starlight as it passes through a planet’s atmosphere during a transit. As the light filters through, molecules in the atmosphere absorb specific wavelengths, leaving behind a telltale spectrum that scientists can decode.

In a series of observations published in early 2025, JWST’s Near Infrared Spectrograph (NIRSpec) and Near Infrared Imager and Slitless Spectrograph (NIRISS) were used to study K2-18b’s atmosphere. Researchers detected significant quantities of methane (CH₄) and carbon dioxide (CO₂), both of which are considered important for understanding planetary habitability.

However, the most tantalizing finding was the potential detection of dimethyl sulfide (DMS), a molecule that, on Earth, is produced almost exclusively by biological processes, particularly by marine phytoplankton.

The presence of DMS is intriguing because it is not known to be produced in significant quantities by non-biological processes on Earth. Its detection on K2-18b, therefore, raises the possibility, though not the certainty, of biological activity. As Dr. Nikku Madhusudhan, the study’s principal investigator, stated in a NASA press release, “Our findings are a promising step toward a deeper understanding of Hycean worlds in this quest” for life beyond Earth.

Despite the excitement, the scientific community has urged caution. The detection of DMS is based on subtle features in the JWST data, and alternative, non-biological explanations for its presence have not been entirely ruled out. Some laboratory experiments suggest that DMS can be produced abiotically under certain conditions, and the interpretation of spectroscopic data from such distant worlds is inherently challenging, the National Center for Biotechnology Information writes.

What is clear, however, is that a new era in the remote exploration of exoplanets has been enabled. The ability to analyze the atmospheric composition of a planet over 100 light-years away, and to search for molecules associated with life, would have been unimaginable just a decade ago. As more data are collected and analyzed, and as JWST’s Mid-Infrared Instrument (MIRI) is brought to bear on K2-18b, the coming months may yield even more definitive answers about the planet’s potential for habitability.