Scientists find 'strongest evidence yet' of life on distant planet

Scientists have found new but tentative evidence that a faraway world orbiting another star may be home to life.

A Cambridge team studying the atmosphere of a planet called K2-18b has detected signs of molecules which on Earth are only produced by simple organisms.

This is the second, and more promising, time chemicals associated with life have been detected in the planet's atmosphere by Nasa's James Webb Space Telescope (JWST).

But the team and independent astronomers stress that more data is needed to confirm these results.

The lead researcher, Prof Nikku Madhusudhan, told me at his lab at Cambridge University's Institute of Astronomy that he hopes to obtain the clinching evidence soon.

"This is the strongest evidence yet there is possibly life out there. I can realistically say that we can confirm this signal within one to two years."

K2-18b is a planet that’s about 2.5 times bigger than Earth and is extremely far away — around 700 trillion miles, or 124 light years. That’s way too far for humans to ever travel.

The James Webb Space Telescope (JWST) is powerful enough to study the planet’s atmosphere by looking at the light from its small red star passing through it.

Scientists at Cambridge found signs in the atmosphere of gases that may be linked to life: dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). On Earth, these gases are made by tiny sea creatures and bacteria.

Professor Madhusudhan said he was surprised by how much of this gas was found in just one observation. He explained that the amount seems to be thousands of times higher than what we see on Earth.

He said, "If these gases really do mean life is there, then the planet could be full of living things."

He also said that if life is confirmed on K2-18b, it would strongly suggest that life is common across the galaxy.

In a radio interview, he said, "This is a big moment for science and also for all of us as humans. If there’s life on one planet out there, then there could be life on many more."

Dr. Subir Sarkar, another scientist on the team from Cardiff University, said the planet might have an ocean that could support life — though they’re not sure yet. He added that the team will keep looking for signs of life on other planets.

"Keep watching this space," he said.

There are still a lot of uncertainties and questions, which even Professor Madhusudhan's team openly admits.

First of all, their latest findings are not strong enough to be called a discovery yet.

To officially claim a discovery, scientists need to be 99.99999% sure their results are real and not just random chance. This level of certainty is called a five sigma result in science.

Right now, their results are only at three sigma, or 99.7% certainty. That sounds high, but it’s not enough to convince most scientists. Still, it’s a big improvement from 18 months ago, when they had only 68% certainty — which many experts didn’t take seriously.

Even if they eventually reach five sigma, that still wouldn’t prove there’s life on the planet, according to Professor Catherine Heymans, an astronomer not involved in the research.

She explained that just finding the gas isn’t enough. On Earth, it's made by ocean microbes, but we can’t be sure it came from life on another planet. There might be unknown natural processes that could also make the gas.

The Cambridge team agrees. They’re now working with other scientists to see if the gases DMS and DMDS could be made without life in a lab setting.

“There’s still a 0.3% chance it could just be a random error,” Prof Madhusudhan said.

He told BBC Radio that suggesting there might be life is a huge claim, so the team wants to be very careful. They plan to collect more evidence until there's less than a one-in-a-million chance it’s a mistake — which they hope to achieve in one or two years.

Meanwhile, other scientists have different ideas. Some disagree about whether those life-related gases are even there, or what the planet is made of.

One theory says the planet may have a huge ocean, because ammonia is missing from its atmosphere — and it may be dissolved in the water.

But another explanation is that the planet might have an ocean of molten rock, which would not support life, according to Professor Oliver Shorttle of Cambridge.

He explained that all we know about planets like K2-18b comes from tiny bits of light that pass through their atmospheres — and reading those signals is very difficult.

So far, scientists are still debating what kind of planet K2-18b really is.

And at NASA, Dr. Nicolas Wogan has yet another interpretation of the data.

Both these alternative interpretations have also been challenged by other groups on the grounds that they are inconsistent with the data from JWST, compounding the strong scientific debate surrounding K2-18b.

Prof Chris Lintott, presenter of the BBC's The Sky at Night, said he had "great admiration" for Prof Madhusudhan's team, but was treating the research with caution.

"I think we've got to be very careful about claiming that this is 'a moment' on the search to life. We've [had] such moments before," he told Today.

He said the research should be seen instead as "part of a huge effort to try and understand what's out there in the cosmos".

Prof Madhusudhan acknowledges that there is still a scientific mountain to climb if he is to answer one of the biggest questions in science. But he believes he and his team are on the right track.