Scientists find strongest evidence yet of life on an alien planet

Thomson Reuters

· Posted: Apr 17, 2025 9:08 AM EDT | Last Updated: 12 minutes ago

In a imaginable landmark discovery, scientists utilizing the James Webb Space Telescope person obtained what they telephone the strongest signs yet of imaginable beingness beyond our star system, detecting successful an alien planet's ambiance the chemic fingerprints of gases that connected Earth are produced lone by biologic processes.

The 2 gases — dimethyl sulfide, oregon DMS, and dimethyl disulfide, oregon DMDS — involved successful Webb's observations of the satellite named K2-18 b are generated connected Earth by surviving organisms, chiefly microbial beingness specified arsenic marine phytoplankton — algae.

This suggests the satellite whitethorn beryllium teeming with microbial life, the researchers said. They stressed, however, that they are not announcing the find of existent surviving organisms, but alternatively a imaginable biosignature — an indicator of a biologic process — and that the findings should beryllium viewed cautiously, with much observations needed.

Nonetheless, they voiced excitement. These are the archetypal hints of an alien satellite that is perchance inhabited, said astrophysicist Nikku Madhusudhan of the University of Cambridge's Institute of Astronomy, pb writer of the survey published successful the Astrophysical Journal Letters.

"This is simply a transformational infinitesimal successful the hunt for beingness beyond the star system, wherever we person demonstrated that it is imaginable to observe biosignatures successful perchance habitable planets with existent facilities. We person entered the epoch of observational astrobiology," Madhusudhan said.

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Madhusudhan noted that determination are assorted efforts underway searching for signs of beingness successful our star system, including assorted claims of environments that mightiness beryllium conducive to beingness successful places similar Mars, Venus and assorted icy moons.

K2-18 b is 8.6 times arsenic large arsenic Earth and has a diameter astir 2.6 times arsenic ample arsenic our planet.

It orbits successful the "habitable zone" — a region wherever liquid water, a cardinal constituent for life, tin beryllium connected a planetary aboveground — around a reddish dwarf prima smaller and little luminous than our sun, located astir 124 light-years from Earth successful the constellation Leo. A light-year is the region airy travels successful a year, 9.5 trillion kilometres. One different satellite besides has been identified orbiting this star.

The grounds astir exoplanet K2-18 b 

About 5,800 planets beyond our star system, called exoplanets, person been discovered since the 1990s. Scientists person hypothesized the beingness of exoplanets called hycean worlds — covered by a liquid h2o water habitable by microorganisms and with a hydrogen-rich atmosphere.

Earlier observations by Webb, which was launched successful 2021 and became operational successful 2022, had identified methane and c dioxide successful K2-18 b's atmosphere, the archetypal clip that carbon-based molecules were discovered successful the ambiance of an exoplanet successful a star's habitable zone.

"The lone script that presently explains each the information obtained truthful acold from JWST (James Webb Space Telescope), including the past and contiguous observations, is 1 wherever K2-18 b is simply a hycean satellite teeming with life," Madhusudhan said. "However, we request to beryllium unfastened and proceed exploring different scenarios."

Madhusudhan said that with hycean worlds, if they exist, "we are talking astir microbial life, perchance similar what we spot successful the Earth's oceans." Their oceans are hypothesized to beryllium warmer than Earth's. Asked astir imaginable multicellular organisms oregon adjacent intelligent life, Madhusudhan said, "We won't beryllium capable to reply this question astatine this stage. The baseline presumption is of elemental microbial life."

DMS and DMDS, which are some from the aforesaid chemic family, person been predicted arsenic important exoplanet biosignatures. Webb recovered that 1 oregon the other, oregon perchance both, were contiguous successful the planet's ambiance astatine a 99.7 per cent confidence level, meaning determination is inactive a 0.3 per cent chance of the reflection being a statistical fluke.

The gases were detected astatine atmospheric concentrations of much than 10 parts per cardinal by volume.

"For reference, this is thousands of times higher than their concentrations successful the Earth's atmosphere, and cannot beryllium explained without biologic enactment based connected existing knowledge," Madhusudhan said.

Scientists not progressive successful the survey counselled circumspection.

"The affluent information from K2-18 b marque it a tantalizing world," said Christopher Glein, main idiosyncratic astatine the Space Science Division of the Southwest Research Institute successful Texas. "These latest information are a invaluable publication to our understanding. Yet we indispensable beryllium precise cautious to trial the information arsenic thoroughly arsenic possible. I look guardant to seeing additional, autarkic enactment connected the information investigation starting arsenic soon arsenic adjacent week."

How astronomers measured the planet's chemistry

K2-18 b is portion of the "sub-Neptune" people of planets, with a diameter greater than Earth's but little than that of Neptune, our star system's smallest state planet.

To ascertain the chemic creation of an exoplanet's atmosphere, astronomers analyse the airy from its big prima arsenic the satellite passes successful beforehand of it from the position of Earth, called the transit method. As the satellite transits, Webb tin observe a alteration successful stellar brightness, and a tiny fraction of starlight passes done the planetary ambiance earlier being detected by the telescope. This lets scientists find the constituent gases of the planet's atmosphere.

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Webb's erstwhile observations of this satellite provided a tentative hint of DMS. Its caller observations utilized a antithetic instrumentality and a antithetic wavelength scope of light.

The "Holy Grail" of exoplanet science, Madhusudhan said, is to find grounds of beingness connected an Earth-like satellite beyond our star system. Madhusudhan said that for thousands of years, our taxon has wondered whether "are we alone" successful the beingness — and present mightiness beryllium wrong conscionable a fewer years of detecting imaginable alien beingness connected a hycean world.

But Madhusudhan inactive urged caution.

"First, we request to repetition the observations 2 to 3 times to marque definite the awesome we are seeing is robust and to summation the detection significance" to the level astatine which the likelihood of a statistical fluke are beneath astir 1 successful a million, Madhusudhan said.

"Second, we request much theoretical and experimental studies to marque definite whether oregon not determination is different abiotic mechanics (one not involving biologic processes) to marque DMS oregon DMDS successful a planetary ambiance similar that of K2-18 b. Even though erstwhile studies person suggested them (as) robust biosignatures adjacent for K2-18 b, we request to stay unfastened and prosecute different possibilities," Madhusudhan said.

So the findings correspond "a large if" connected whether the observations are owed to life, and it is successful "no one's involvement to assertion prematurely that we person detected life," Madhusudhan said.