Astronomers continue to debate the strongest evidence for extraterrestrial life

Astronomers claim they have seen the most powerful evidence ever for living on another planet. However, other astronomers are cautioning until the findings are verified by other groups, allowing alternative, nonbiological explanations to be excluded.

“These are the first hints we see about the alien world we probably live in.” Nick Madhusdan We held a press conference at Cambridge University on March 15th.

Astronomers first discovered the Exoplanet K2-18B in 2015, quickly establishing it as a promising place for searching for life. Planets orbiting stars about eight times more than Earth, 124 light years away from us, sit in a habitable zone of stars where liquid water is present. Further observations in 2019 found evidence of water vapor. This led to the suggestion that, although not all astronomers agreed, the planet could be covered in oceans sitting under a hydrogen-rich atmosphere.

In 2023, Madhusudhan and his colleagues used James Webb Space Telescope (JWST) instruments to examine the atmosphere of the near-infrared light K2-18B, again finding evidence of water vapor and methane. However, they also found appetizing hints for dimethyl sulfide (DMS), a molecule that is produced exclusively by organisms on Earth, primarily by marine phytoplankton. However, the signs of DMS were very weak and many The astronomers argued Stronger evidence is needed to be certain about the existence of molecules.

Currently, Madhusudhan and his colleagues use different instruments to observe the K2-18b than the mid-infrared camera JWST. They discovered a much stronger signal against DMS and a molecule that could be called dimethyldisulfide (DMDS).

“What we’re finding is a line of independent evidence in different wavelength ranges with different equipment that can potentially biological activity on the planet,” Madhusdan said.

The team argues that detection of DMS and DMD is at three sigma levels of statistical significance. This corresponds to a 1/100 chance that a pattern of data like this will become absorption. In physics, the standard threshold for accepting something as a true discovery is five sigmas, which corresponds to 1-3.5 million chances that data is a coincidence.

Nicholas Wargan The NASA Ames Research Center in California says the evidence is more convincing than the 2023 results, but it should be verified by other groups. When data is published next week, other researchers can begin to review the findings, but this could take weeks or months as JWST data is difficult to interpret. “It’s not just about downloading data and checking if there’s a DMS. It’s this extremely complicated process,” says Wogan.

Other scientists are more skeptical of the findings. “These new JWST observations do not provide compelling evidence that DMS or DMD exists in the atmosphere of K2-18B.” Ryan McDonald At the University of Michigan. “We have a juvenile chase wolf situation in the K2-18B, where multiple previous 3-sigma detections have completely disappeared when subjected to closer scrutiny.

Madhusudhan and his team estimate that further 16 to 24 hours of further observations at the JWST will help reach 5-sigma levels, but observing the planet’s atmosphere means that this cannot be guaranteed.

“The relative size of the atmosphere compared to the planet’s size is pretty close to the thickness of the apple’s skin on top of the apple, which is what we’re trying to measure.” Thomas Beatty At the University of Wisconsin-Madison, where I was not part of the learning team. Wogan adds that reaching five sigmas may be fundamentally impossible due to the amount of noise in the data.

But if further observations prove that this is a real discovery, it would be a “risqué progress,” says Beatty. “Ignoring whether it was actually being produced for a moment, I said that ten years ago it is evidence of life in a planetary atmosphere that can certainly host it.”

Madhusudhan and his colleagues calculate that the potential concentration of DMS and DMD in K2-18B appears to be over ten parts, thousands of times more than the concentrations in the Earth’s atmosphere. This could show far more biological activity than Earth if the signal turns out to be correct, but establishing that chemicals have biological origins requires more work, he says.

“We need to be very careful,” Madhusdan said. “At this stage, when you detect DMS and DMD, you can’t claim it’s for life. Let’s be very clear about that.

It could take some time to eliminate another mechanism, Wogan says. “This kind of thing hasn’t been studied in practice. In a hydrogen-rich atmosphere, DM doesn’t know tons about it. It requires a lot of work.”

The difficulty in proving that it has no nonbiological explanations is that it could potentially put K2-18B in the category of viable biosignature candidates over a long period of time. Sarah Seager At Massachusetts Institute of Technology. “It could remain in that category for decades, because the problem will not be completely solved by providing limited data deplanets,” she says.

However, Madhusudhan says this discovery is important whether it comes from life or not. “This was a revolutionary moment, and we were able to come from a single cell life, not just as astronomers, but also for our species, from a single cell life billions of years ago, to a highly technological civilization where we could peer into the atmosphere of another planet and find evidence of actual biological activity,” he said.

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