Astronomers claim to have discovered the strongest signs yet of possible life on a planet 700 trillion miles away from Earth.

The scientists from the University of Cambridge used a mid-infrared camera from the James Webb Space Telescope (JWST) to observe exoplanet K2-18b, a planet that is not in our solar system and is eight times the size of Earth, orbiting a star 124 light years away.

The planet was first discovered in 2017 by Canadian astronomers while looking through ground-based telescopes in Chile, according to the New York Times. The “hycean planet,” meaning it’s home to an abundance of a life-signifying molecule, is at the centre of a new study published in Astrophysical Journal Letters.

The astronomers detected the chemical fingerprints of gases in the alien planet’s atmosphere that are only produced by biological processes on Earth.

The two gases — dimethyl sulphide (DMS) and dimethyl disulphide (DMDS) — involved in the observations of K2-18b are generated on Earth by living organisms, primarily microbial life such as marine phytoplankton, commonly known as algae.

This suggests the planet may be teeming with microbial life, researchers said.

“These are the first hints we are seeing of an alien world that is possibly inhabited,” Nikku Madhusudhan of the University of Cambridge’s Institute of Astronomy said in a press conference on Tuesday. “It is in no one’s interest to claim prematurely that we have detected life.

“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.”

Madhusudhan, the lead author of the Astrophysical Journal Letters study, noted that there are efforts underway searching for signs of life in our solar system, including environments that might be conducive to life in places like Mars, Venus and various icy moons.

The researchers are not announcing the discovery of actual living organisms but rather a possible biosignature — an indicator of a biological process — and say the findings should be viewed cautiously.

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The University of Cambridge’s findings have reached the “three-sigma” level of statistical significance, meaning there is a 0.3 per cent probability that they occurred by chance, according to the report. To reach the accepted classification for scientific discovery, the report stated that observations would have to cross the “five-sigma threshold,” meaning there would be “a below 0.000006 per cent probability they occurred by chance.”

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Other astronomers have urged caution on the new findings until they can be verified by other groups.

“The rich data from K2-18 b make it a tantalizing world,” Christopher Glein, principal scientist at the Space Science Division of the Southwest Research Institute in Texas, told Reuters. “These latest data are a valuable contribution to our understanding. Yet, we must be very careful to test the data as thoroughly as possible. I look forward to seeing additional, independent work on the data analysis starting as soon as next week.”

“Unless we see E.T. waving at us, it’s not going to be a smoking gun,” Glein told the New York Times.

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

Ryan MacDonald at the University of Michigan told New Scientist that the “new JWST observations do not offer convincing evidence that DMS or DMDS are present in K2-18b’s atmosphere.”

“We have a boy-who-cried-wolf situation for K2-18b, where multiple previous three-sigma detections have completely vanished when subject to closer scrutiny. Any claim of life beyond Earth needs to be rigorously checked by other scientists, and unfortunately many previous exciting claims for K2-18b haven’t withstood these independent checks.”

Madhusudan also urged caution, saying, “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.” He wanted to make sure the odds of a statistical fluke are below roughly one in a million.

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

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Earlier observations by JWST, which was launched in 2021 and became operational in 2022, had identified methane and carbon dioxide in K2-18 b’s atmosphere, the first time that carbon-based molecules were discovered in the atmosphere of an exoplanet in a star’s habitable zone.

“The only scenario that currently explains all the data obtained so far from JWST, 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.”

When asked about possible intelligent life on K2-18b during the press conference, Madhusudhan said, “We won’t be able to answer this question at this stage. The baseline assumption is of simple microbial life.”

He said he and his team estimate that between 16 and 24 hours of further observations with JWST could help them reach the five-sigma level.

“Earlier theoretical work had predicted that high levels of sulphur-based gases like DMS and DMDS are possible on hycean worlds,” Madhusudhan said. “And now we’ve observed it, in line with what was predicted. 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.”

“Our work is the starting point for all the investigations that are now needed to confirm and understand the implications of these exciting findings,” said co-author Savvas Constantinou, also from Cambridge’s Institute of Astronomy.

This isn’t the first time astronomers claimed to have detected alien life.

In September 2020, astronomers said they detected a chemical in the Venusian clouds that likely could only be produced by organic life. Two telescopes detected the presence of phosphine in the clouds over Venus, according to a study published in Nature and another submitted to the journal Astrobiology. The chemical only comes from factories and microbes living in oxygen-free environments on Earth, and there is no other known natural process for producing it.

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That means there’s no way the chemical should exist in this form except “from the presence of life” or through some bit of never-before-seen chemistry, according to the study authors.

“I was just stunned,” said Jane Greaves, the lead study author and a professor at Cardiff University in the United Kingdom.

The discovery was not proof of life, but it was a good lead that could help astronomers narrow the scope on what sort of aliens they should be looking for on Venus, according to Greaves.

— With files from Global News and Reuters