James Webb Space Telescope (JWST), illustration. This infrared telescope launched in December 2021. Photo: JAMES VAUGHAN/SCIENCE PHOTO LIBR/AFP
Astronomers have just uncovered fascinating signs we may not be alone in the universe - but what exactly does the discovery tell us, and why is it unusual?
The team from the University of Cambridge say they detected a biosignature - special molecules in the atmosphere of a distant exoplanet. They have called it a revolutionary moment. But not everyone is convinced.
Other scientists are urging caution, saying we need more proof before we can declare that the observations mean there is life on another planet.
RNZ's Nights talked with Professor Jan Eldridge, the University of Auckland's head of physics, about the discovery.
What is planet K2-18b like?
The observation was seen on a large exoplanet, which is currently called K2-18b, and is 124 light years away from Earth.
"It's a planet that's bigger than Earth ... it's something we call a Super-Earth or a Super-Neptune... it's about eight times the mass of Earth but only about 2.6 times the radius, so the density is about the same," Eldridge says.
Some planets are thought to be made up of gas and liquids, while others are rocky, but scientists don't yet know the form of this planet.
It is currently thought it could be a 'hycean world' - a water world with a hydrogen-rich atmosphere, but studies into what type of surface it has are underway.
Professor Jan Eldridge says the discovery is exciting science, but doesn't mean we've found alien life. Photo: Supplied/ University of Auckland - Elise Manahan
"The star it's orbiting is actually very different from our sun, it's about half the mass of the sun so it's actually quite a red star. The planet's actually orbiting much closer to its host star than our Earth does, and it's only got a 33-day year," Eldridge says. "So it's a very unusual planet compared to anything in our solar system."
This exoplanet falls inside a 'habitable zone', which Eldridge says are areas around each star where scientists believe conditions exist that could allow atmospheres which could support liquid water existing on planet surfaces.
"You need liquid water, it's a wonderful solvent, it's got really interesting chemistry and ... that's why we exist, because there's water in our cells - we're 70 percent water," she says.
What exactly did the team find?
The new observation, made using the James Webb Space Telescope, spotted a chemical that could be a signature of life - dimethyl sulfide (DMS) - a molecule that is also found on Earth, where it is created by marine algae.
"But that's only one signature molecule, and even if we see something, we don't know if there's other processes that could make it," Eldridge says.
"There's a saying among astronomers - 'it's never aliens', even if we think it could be - and so whenever we see something like this we say 'really?'"
In 2019, a team of scientists said the planet K2-18b was the only known rare Super-Earth exoplanet with signs that it hosts water and temperatures that could support life. Photo: M. KORNMESSER / ESA/Hubble / AFP
Eldridge says the newly published scientific paper about the discovery of dimethyl sulfide on K2-18b, which was written by the researchers who worked on this project, was not quite as confident as the press releases that accompanied it and provide a simplified condensed take on the findings.
"But what's exciting is ... detecting what's in the atmospheres of exoplanets is extremely difficult," she says.
"If you find something exciting it's worthwhile going as exciting as you can ...because you get people talking about science, which is a really important thing, but you've always got to caution things because it's very easy to ... get too excited."
How did the team find the molecule, and what does spotting it tell us?
Eldridge says the team used the James Webb Space Telescope, which is currently orbiting our sun, and trained it on the star the exoplanet K2-18b is orbiting to watch for the transit - when the exoplanet passes across the telescope's view of the star.
"You're looking at the star and you're waiting for the planet to go in front of the star, and when it goes in front of the star the planet blocks out some of the light of the star, but some of that light also goes through the atmosphere. ... We split the light up and we compare the spectrum before the transit and during the transit ....and we see what the atmosphere is [made up of].
"We know from this planet from previous observations that it had carbon dioxide, that it had methane and possibly water, but this is the first time we've seen this dimethyl sulfide, which is a possible biomarker.
"So even ignoring if that means there is life there, it's an enormous achievement just even to find the signal of this new molecule that hasn't been seen in any other exoplanet."
And this is where Eldridge urges people to not read too far into the finding.
"It's really really difficult work to do, which is why so many other people are sceptical about this - because other groups have looked at similar data and they haven't seen the molecule. But maybe it's more complicated than that - maybe there's a cycle and some days it's there and some days it's not?
"This is why we do caution, and try and say that it's there - but give us time to work out and see what else is going on with this planet."
A rendering released on Thursday by the University of Cambridge, depicting the exoplanet K2-18b, where they say they have found the strongest yet 'hints' of life possibly existing outside our solar system. Photo: AFP PHOTO / UNIVERSITY OF CAMBRIDGE / N. MADHUSUDHAN
Eldridge says other research has indicated the same molecule could have been found on comets that are going around our sun.
"So there are indications that there could be other ways of making this molecule which we don't know."
And a few years ago a biosignature was found on Venus, but that signal had later gone away, she says.
"I think one day we're definitely going to find more planets soon with more of these biomarkers - that could indicate life there - but trying to prove that there's life in these planets is actually really difficult. And I think we can solve it, but it's very tricky to say that 'this is life' straight away, until we actually have confirmation and somebody else has found the same molecule."
Listen to the full interview here.
