JWST finds hints of life on alien world

A tantalising sign of alien life may have just been discovered on a distant exoplanet by NASA’s James Webb Space Telescope (JWST).

The telescope has made a potential detection of dimethyl sulphide (DMS) – a chemical that, on Earth, is only produced by life – in the atmosphere of potentially habitable world, K2-18 b.

However, the discovery team were keen to emphasise the detection is still only tentative, requiring more data to confirm.

The observations did, however, make more robust detections of carbon dioxide and methane, suggesting the planet could be home to a liquid water ocean.

Spectrum of K2-18 b, obtained with Webb’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph), displays an abundance of methane and carbon dioxide in the exoplanet’s atmosphere, as well as a possible detection of a molecule called dimethyl sulfide (DMS). The detection of methane and carbon dioxide, and shortage of ammonia, are consistent with the presence of an ocean underneath a hydrogen-rich atmosphere in K2-18 b. K2-18 b, 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth. [Image description: The graphic shows the spectra of the exoplanet K2-18 b from NIRISS and NIRSpec in the form of a graph, with the vertical y-axis labelled as Amount of Light Blocked and the horizontal axis labelled as Wavelength of Light (microns). The spectra is plotted as dots with vertical short vertical lines across the plot, with the best-fit model as a blue jagged white line.There are green, yellow and light blue vertical columns of varying thicknesses scattered across the plot indicating where variations in the line represent the presence of methane, carbon dioxide, and dimethyl sulphide, respectively. Behind the graph is an illustration of the planet and star.]

“These results are the product of just two observations of K2-18 b, with many more on the way,” says Savvas Constantinou from the University of Cambridge, who took part in the study.

“This means our work here is but an early demonstration of what Webb can observe in habitable-zone exoplanets.”

What kind of planet is K2-18 b?

K2-18b is 120 lightyears away and takes around 33 days to orbit its cool dwarf star.

It is 8.6 times the mass of Earth and 2.6 times its radius, making it a sub-Neptune.

These are planets with masses between Earth and Neptune that appear to be common in the Galaxy.

As there are no examples of these kinds of worlds in our Solar System planetary scientists have little idea of what either they might be like, meaning the worlds have become an area of intense study.

Earth positioned next to the much larger Neptune. — Earth is the largest terrestrial planet in our Solar System, but then there is a jump up to the next largest, Neptune, which is four times the size. Credit: NASA

Previous observations by Hubble in 2019 suggested K2-18 b has an atmosphere.

This makes it a prime target to learn more about these kinds of worlds as JWST is able to detect which chemicals might exist within that atmosphere.

Listen to our interview with Angelos Tsiaras to find out more about the discovery of K2-18 b’s atmosphere.

How did JWST examine K2-18 b’s atmosphere?

JWST watches planets as they pass in front of (or transits) their stars.

As a planet transits, some of the starlight passes through its atmosphere, during which some of the chemicals in the atmosphere leave behind a signature in the light.

Astronomers are able to interpret these signatures to work out the composition of the atmosphere of these distant worlds.

Discover how you can detect exoplanets from your own back garden.

A planet transits in front of its star. — Astronomers will be able to search for atmospheric biosignaturesin transiting exoplanets. Credit: NASA

JWST detected various carbon molecules in K2-18 b’s atmosphere, including carbon dioxide and methane, but little ammonia.

This is what you would expect to see on a Hycean exoplanet – worlds up with up to 10 times the mass of Earth with a hydrogen atmosphere and which are thought to be covered with a liquid water ocean.

These are thought to be one of the most likely places to find life beyond Earth.

“Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere,” explained Nikku Madhusudhan, from University of Cambridge who led the study.

“Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger Hycean worlds are significantly more conducive to atmospheric observations.”

An icy planet with a small, reddish star in the distance. A thin atmosphere is visible above the planet. — *Hycean exoplanets are thought to be in their planet’s habitable zone, where liquid water oceans can exist on the surface. Credit: NASA*

Did JWST find life on K2-18 b?

JWST’s observations also found a hint of dimethyl sulphide (DMS).

Here on Earth, the chemical is only known to be produced by life, with the bulk of the chemical in the planet’s atmosphere created by tiny marine algae, phytoplankton.

This detection, however, was not as robust as the others and so will require further validation.

“Upcoming [JWST] observations should be able to confirm if DMS is indeed present in the atmosphere of K2-18b at significant levels,” says Madhusudhan.

Long thing green cells of phytoplankton viewed under a microscope — Algae cells under microscope magnification 10X

Even if DMS is present, that doesn’t mean that life has been detected on K2-18 b. Though there are no known geological or chemical processes on Earth that produce DMS naturally, the same may not be true on a sub-Neptune.

The planet is also very close to its star, meaning it is bombarded with a great deal of high-energy radiation, which any organisms on its surface would have to be able to survive.

It’s also worth noting that the planet is 120 lightyears away, meaning that even if we could travel at nearly the speed of light, it would take more than a lifetime to reach the planet.

However, the discovery is an exciting first step on the journey towards finding life beyond our planet.

“Our ultimate goal is the identification of life on a habitable exoplanet, which would transform our understanding of our place in the universe,” concluded Madhusudhan. “Our findings are a promising step towards a deeper understanding of Hycean worlds in this quest.”