Astronomers claim the strongest evidence of extraterrestrial life to date

Astronomers claim to have seen the strongest evidence so far for Life on another planet. But other astronomers have urged caution Until the results can be checked by other groups and non -biological explanations can be excluded.

“These are the first clues we see from an extraterrestrial world that may be inhabited,” Nikku Madhusudhan At the University of Cambridge declared a press conference on March 15.

Astronomers discovered the K2-18B exoplanet in 2015 and quickly established that it was a promising place to look for life. About eight times as massive as the earth and orbit around a 124-light year star far from us, the planet is in the habitable area of ​​its star, where liquid water can exist. Other observations, in 2019, found proof of water vapor, which led to suggestions that the planet can be covered in the oceans seated under an atmosphere rich in hydrogen, although Not all astronomers have accepted.

In 2023, Madhusudhan and his colleagues used the instruments of the James Webb space telescope (JWST) to look at the atmosphere of K2-18B under the close infrared light, and again found proof of water vapor, as well as carbon dioxide and methane. But they also found an enticing suspicion of dimethyl sulfide (DMS), a molecule which, on earth, is only produced by living organisms, mainly sea phytoplankton. The signs for DMs were extremely weak, however, and many Astronomers have argued that we would need much stronger evidence to be sure of the presence of the molecule.

Now Madhusudhan and his colleagues have used a different instrument from JWST, the average infrared camera, to observe K2-18B. They found a much stronger signal for the DMS, as well as a possible related molecule called dimethyle disulfide (DMD), which is also produced on earth only by life.

“What we find is an independent line of evidence in a range of different wavelengths with a different instrument of possible biological activity on the planet,” said Madhusudhan.

The team claims that the detection of DMS and DMD is at three SIGMA of statistical meaning, which is equivalent to a chance of 3 in 1000 that a data model like this ends up being a stroke of luck. In physics, the standard threshold to accept something like a real discovery is five sigma, which is equivalent to a 1.5 million chance on the 1.5 million chances that the data is a chance.

Nicholas Wogan At NASA Ames Research Center in California, the evidence is more convincing than the 2023 results, but it must still be checked by other groups. Once the data is made public next week, other researchers can start to confirm the results, but it could take weeks or months due to the difficulty of interpreting JWST data. “It's not just as if you download the data and see if there is DMS – it's this super complicated process,” said Wogan.

Other scientists are more skeptical about the results. “These new JWST observations do not offer convincing evidence that DMDs or DMDs are present in the atmosphere of K2-18B,” said Ryan Macdonald at the University of Michigan. “We have a situation of Loup-Loup-Créé for K2-18B, where several previous detections of three SIGMA have completely disappeared when they are subject to a more in-depth examination. Any claim of life beyond the earth must be rigorously verified by other scientists, and unfortunately many exciting affirmations previous for K2-18B have not known these independent checks. “

Madhusudhan and his team believe that between 16 and 24 hours of additional observations with JWST could help them reach the level of five Sigma, but the difficulty of observing the atmosphere of the planet means that they cannot guarantee this.

“The relative size of the atmosphere compared to the size of the planet is quite close to the thickness of an apple skin above an apple. This is what we are trying to measure, ”says Thomas Beatty At the University of Wisconsin-Madison, which was not part of the study team. Wogan adds that access to five sigma could be fundamentally impossible due to the amount of noise in the data.

But if other observations can prove that it is a real discovery, it would be a “great advance”, explains Beatty. “Ignoring whether or not it is really produced by life for a second, it is something that, a decade ago, people said it would be proof of life in the atmosphere of a planet that could host it.”

Madhusudhan and his colleagues calculate that the possible concentrations of DMS and DMD on K2-18B seem to exceed 10 parts per million, thousands of times more than the concentrations of the earth's atmosphere. This could indicate a large amount of biological activity on earth, if the signal is correct, but establishing that chemicals have a biological origin will take more work, he says.

“We must be extremely cautious,” said Madhusudhan. “We cannot at this stage of this stage that, even if we detect DM and DMDs, this is due to life. Allow me to be very clear on this subject. But if you take studies published so far, there is no mechanism that can explain what we see without life.”

Vitting alternative mechanisms could take some time, explains Wogan. “Something like it has not really been studied. DMS in an atmosphere rich in hydrogen, we do not know a ton about it. There should be a lot of work.”

The difficulty in proving that she could not have a non-biological explanation could place K2-18B in the category of a viable biosignature candidate for a long time, said for a long time Sara Seager at the Massachusetts Institute of Technology. “It can remain in this category for decades, because the question may never be fully resolved with the limited data that exoplanets offer,” she says.

Madhusudhan, however, says that the observation is important, whether it came from life or not. “It is a revolutionary moment, fundamentally for me as an astronomer, but also for our species-that we have come from single cell life, billions of years ago, to an advanced technological civilization which is capable of looking in the atmosphere of another planet and to find evidence for a possible biological activity,” he said.

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