Hopes of finding aliens were raised in 2025 – but quickly faded

The search for life beyond the solar system intensified this year as scientists… reported a teasing signal from an exoplanet molecule that is known to be produced exclusively by life on Earth. Those hopes soon faded when other teams failed to confirm the detection, but the heated debate that followed was a good learning process for potential alien observers, exoplanet researchers say.

In April Nikku Madhusudhan from the University of Cambridge and his colleagues announced at a press conference that they had seen “the first hints… of an alien world that may be habitable.” These hints came from K2-18b, a planet about eight times more massive than Earth, 124 light-years from Earth and in the habitable zone of its star, which they observed with the James Webb Space Telescope (JWST).

Infrared light from K2-18b suggested that its atmosphere may contain a molecule called dimethyl sulfide (DMS), which on Earth is produced only by living organisms, primarily marine phytoplankton.

This news, as expected, caused a stir among the world media and the scientific community. But along with the excitement, many researchers are also urging caution. According to them, the DMS signal was extremely weak and would require many follow-up observations and further analysis to confirm it.

Now, after several months of additional observations and thorough analysismost astronomers agree that we cannot say that DMS, or anything similar to a biomolecule, exists in K2-18b atmosphere – and if there is, we cannot detect it at present. “The only two things we know for sure are that there is methane and carbon dioxide in the atmosphere of this planet,” says Louis Wellbanks at Arizona State University.

The claim that we could see alien life was premature, says Welbanks. “This has been shown repeatedly to be incorrect. New observations show that these gases are not present,” Welbanks says.

However, the spike in data that was initially attributed to DMS still requires explanation, he says. Jake Taylor at Oxford University. “There's this lump there. It's physical. We can see it. We just don't know what the explanation is right now.”

Figuring out which molecule is causing the burst will require additional observations of the planet, which JWST plans to do next year, Taylor said. Scientists can only measure what's in a planet's atmosphere by using the starlight that passes through it when the planet moves in front of its star, which happens four times every Earth year.

Despite all the controversy surrounding the controversial discovery, it has led to some positive results, Taylor said. “It's been a really good learning process for the exoplanet community as a whole. Now we're back to the drawing board in terms of what definitions we should use for different statistical methods. It's been really, really helpful for us,” he says.

“It helps us learn to adjust our expectations,” Welbanks says. “The lesson here is that if you have to play with numbers to make a claim about something, it's really hard. Someone smarter than me said there are lies, damned lies and statistics. This whole DMS thing falls into that category.”

Secrets of the Universe: Cheshire, England

Spend a weekend with some of science's brightest minds as you explore the mysteries of the universe on an exciting program that includes a tour to see the famous Lovell Telescope.