Last week, astronomers led by a team at the University of Cambridge announced a first-of-its-kind detection of possible signs of life on another planet. Specifically, they found evidence of molecules in the atmosphere of planet K2-18b that, as far as we know, are only produced by biological organisms. These researchers and expert commentators have been cautious when discussing this discovery – they are reporting possible signs of life, not life itself – but the astronomical community is still abuzz with the implications.

What does a Stanford exoplanet expert have to say? Aliens or no, it is noteworthy that the observations exist at all, explained Laura Schaefer, assistant professor of Earth and planetary sciences in the Stanford Doerr School of Sustainability.

Laura Schaefer | Courtesy Laura Schaefer

“This is one of the first atmospheric detections of a planet that is relatively small (in comparison to the gas giants) and that has the potential to be a habitable planet,” said Schaefer.

Analyzing the starlight that filters through an exoplanet’s atmosphere is currently one of the few ways we can search for faraway life. And, believe it or not, we don’t have the technological capabilities to measure the atmospheres of planets that are both Earth-like and at the right distance from their stars to support life. For better and worse, K2-18b is too large to be considered Earth-like – which is why we can analyze its atmosphere – but it’s in a habitable zone.

To learn more about this exciting discovery – and whether Schaefer herself is thinking “aliens!” – we asked our expert four of our most pressing questions.

Would we expect this to be a habitable planet?

K2-18b is about the same temperature as Earth and is in its star’s habitable zone. So, it has those things going for it.

K2-18b is also nine times more massive than the Earth, but its density is much lower, and we’re still not entirely sure why. There are two possible explanations, and one is that it has a thick layer of water – possibly a global ocean – which sounds quite habitable. But it’s hard to say if that’s the case because this is a planet with a mass that is somewhere between Earth and Neptune/Uranus, and we don’t have that in the solar system. So, we just don’t really know much about planets like this.

What did this new research find?

What they have found is a tentative detection of two molecules: dimethyl sulfide and dimethyl disulfide. These are interesting compounds because, on Earth, they are produced by biology – specifically phytoplankton in the oceans.

A couple important details to add: the only potential source we can think of that could explain these observations would be a fairly advanced biological production mechanism. Also, these molecules are pretty fragile in the atmosphere; they get destroyed easily by sunlight coming in. And so, to have this big of a signal, you would need near-constant production coming up from the surface. So, not only some advanced biology, but a lot of it.

People should also know that dimethyl sulfide is not a super common molecule, so there’s just not a lot of laboratory data on it. That means that it’s possible that the models are just missing data that would help us determine how it could be produced without a biological organism involved.

K2-18b is 120 light-years away. How much more can we find out about something so distant?

These observations, which were taken with the James Webb Space Telescope, are a step in the right direction. If the community thinks it’s valuable, we could devote more time to additional observations with JWST and see if we can get a sharper signal. We could also potentially use Hubble to look at this planet to try to detect other wavelengths, which might offer complementary information.

Otherwise, we’re sort of stuck waiting for future telescopes. There are future, large, ground-based telescopes that could potentially make some observations of this planet that would be helpful. And then the next generation of NASA telescope, which is in the planning stages, is called the Habitable Worlds Observatory, and it’s designed to make this kind of observation. So, stay tuned in a couple of decades!

So … is it aliens?

More than likely, it’s not.

This research found a tantalizing hint at something that could potentially turn out to be a biosignature. But we want to always be cautious with making extraordinary claims.

This is the very first analysis of new observational data that has been made available. As the data becomes available to more people, it might result in other interpretations – either of the detection or of the idea that they are biosignatures.