Scientists have found a potential sign of life on a distant planet

Though astronomers cannot be sure yet and will have to conduct further tests, there is much excitement about the discovery of a gas that, on Earth, is mostly produced by living organisms.

- By Daniel Apai

A team of astronomers announced on 16 April that, in the process of studying a planet around another star, they had found evidence for an unexpected atmospheric gas called dimethyl sulfide (DMS). On Earth, this gas is mostly produced by living organisms.

In April 2024, the James Webb Space Telescope (JWST) stared at the host star of the planet K2-18b for nearly six hours. During that time, the orbiting planet passed in front of the star. Starlight filtered through its atmosphere, carrying the fingerprints of atmospheric molecules to the telescope.

By comparing those fingerprints to 20 different molecules they would potentially expect to observe in the atmosphere, the astronomers concluded that the most probable match was a gas that, on Earth, is a good indicator of life.

I am an astronomer and astrobiologist who studies planets around other stars and their atmospheres. In my work, I try to understand which nearby planets may be suitable for life.

K2-18b, a mysterious world

To understand what this discovery means, let's start with the bizarre world it was found in. The planet's name is K2-18b, meaning it is the first planet in the 18th planetary system found by the extended NASA Kepler mission, K2. Astronomers assign the “b” label to the first planet in the system, not “a”, to avoid possible confusion with the star.

K2-18b is a little over 120 light years from Earth; on a galactic scale, this world is practically in our backyard.

Although astronomers know very little about K2-18b, we do know that it is very unlike Earth. To start, it is about eight times more massive than Earth, and it has a volume that's about 18 times larger. This means that it's only about half as dense as Earth. In other words, it must have a lot of water, which isn't very dense, or a very big atmosphere, which is even less dense.