From Star Wars to Dune; from The Hitchhiker’s Guide to the Galaxy to ET and even Doctor Who, human beings have been fantasising and writing about the potential of life on other planets for centuries. How might we interact with them? Will they be more intelligent than we are? Should we make contact or should we fear eradication?
The age old question of “should we shoot first” has plagued the minds of physicists and philosophers alike for what feels like an eternity (the answer is no by the way, for all those crazy TPs who think the only right decision is to immediately destroy the first signs of life on another planet).
It’s finally time to turn these thought experiments into a reality as scientists have found evidence of life on another planet in the Milky Way!
ET, the beloved alien from the 1982 science-fiction film.
No need to jump into action straight away though, with your high-tech lasers and explosives. This isn’t a case of Vogons trying to build their hyperspace bypass or Harkonnens coming to desecrate the planet. In fact, the planet in question (K2-18b) is located 124 light years away, so we won’t be arriving there any time soon.
A team at Cambridge University’s Institute of Astronomy used the James Webb Space Telescope to study the atmosphere of K2-18b. How can they tell what’s in the atmosphere of a planet 124 light years away, you might ask? They use a method known as spectroscopy, which analyses the light that passes from the star through the planet’s atmosphere on its way to Earth. Certain wavelengths of light are absorbed by specific chemicals, and so by studying the spectrum of the light that reaches us, we can determine the chemical composition of the planet’s atmosphere.
Figure 1: Schematic of spectroscopic analysis. The dips in intensity (amount of light) come from light absorption due to specific chemicals which can be easily read from the diagram. Image Credit: NASA, ESA, CSA, STScI, Joseph Olmsted (STScI), “Reading an Earth-like Exoplanet’s Transmission Spectrum,” webbtelescope.org, accessed 05/05/25.
It was found that the atmosphere on K2-18b contains at least one of either dimethyl sulphide or dimethyl disulphide, two gases which, here on Earth, are produced by marine phytoplankton and bacteria [1]. The amount of these gases present appears to be significantly higher than on Earth, suggesting the possibility of an ocean-covered planet teeming with life.
You might now be wondering: “If we’ve just discovered aliens, why isn’t this all over the news?” The team is 99.7% certain of their discovery. In technical jargon, this is known as a three-sigma result. For those of you familiar with the normal distribution, this means the reading is within three standard deviations of the expected result. While this might seem like enough to go shouting from the rooftops that we have found aliens, scientists will not claim a discovery until they have a five-sigma result or higher. In other words, until they are 99.99999% sure of their reading. It is also worth keeping in mind that while we associate dimethyl sulphate and dimethyl disulphate with certain living organisms on Earth, there could be a non-biological explanation to these chemical signatures. The team at Cambridge is currently working on trying to generate these chemicals by non-living means in the lab, to see if there could be a geological or other explanation for their presence on K2-18b. This is good news for the world as it demonstrates how committed this team of scientists is to finding the truth, but bad news for the sci-fi enthusiasts who want to see conclusive proof of extra-terrestrial life. I wouldn’t despair though. Professor Nikku Madhusudhan of the Institute of Astronomy at Cambridge said in an interview with the BBC that in “maybe one or two years,” we might know for sure if this is real alien activity or not.
Figure 2: Observed emission spectrum from K2-18b published in the official paper. Can visualize the presence of methyls. Image Source: Michaela Leung, Shang-Min Tsai, Edward W. Schwieterman, Daniel Angerhausen, and Janina Hansen, “Examining the Potential for Methyl Halide Accumulation and Detectability in Possible Hycean-type Atmospheres,” The Astrophysical Journal Letters, Volume 982, Number 1, published 11/03/25.
Alas, it seems that as of yet, we remain lonely in this vast universe. It may not be for long though. Since the launch of the James Webb Space Telescope in 2021, we are seeing major advancements in our observational abilities across the cosmos. Perhaps one day soon we will know if we have neighbours in nearby solar systems, or perhaps even as close as our own! Both Jupiter and Saturn have moons which are viable candidates for life. Or perhaps one day we will simply get blown up to make way for a new hyperspace bypass, and we will never know at all.
[1] Pallab Ghosh, “Scientists find ‘strongest evidence yet’ of life on distant planet”, bbc.com/news, published 17/04/25, accessed 05/05/25.
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