On a huge water world: clearest evidence of extraterrestrial life to date
The exoplanet K2-18 b has long been the focus of research. Now a research team reports that it has discovered the clearest evidence of life there.
Artistic representation of the water world K2-18 b
(Image: University of Cambridge)
A research team using the James Webb Space Telescope (JWST) has discovered what it claims is the clearest evidence yet of extraterrestrial life on the exoplanet K2-18 b, 124 light years away, which is apparently completely covered by an ocean. The University of Cambridge has now made this known and explained that the discovery is further evidence of dimethyl sulphide (DMS), a substance that is only produced by organisms on Earth. The clearest indication of this was discovered using the MIRI instrument, which is designed for the mid-infrared spectrum. It was also used to find the trace of dimethyl disulphide (DMDS), another so-called biosignature.
(Image:Â University of Cambridge)
Detection with the next instrument
K2-18 b has long been considered the most promising candidate in the search for extraterrestrial life, and in the fall of 2023 it was first made public that a biosignature may have been found there using DMS. This is the name given to substances that are attributed to the existence of life. However, the signal presented at the time was rather weak and last spring another research team rejected the conclusion. Now it is said that the measurements with MIRI are much clearer and exceed the threshold of 3 sigma. This means that only 0.3 percent of the signal is due to chance. However, only the significantly higher limit of 5 sigma is considered definitive proof in research.
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So even now it is not a discovery of extraterrestrial life in the scientific sense. However, the discovery is much clearer and therefore the clearest evidence of extraterrestrial life to date. DMS and DMDS are both substances from the same chemical family, but they occur in much lower concentrations in the Earth's atmosphere than apparently on K2-18 b, the team writes. While there is only less than one particle per billion on our home planet, the measurements with the JWST would indicate that there are more than ten per million particles on the exoplanet, i.e. more than a thousand times as many.
“A water world teeming with life”
In view of what we know about this exoplanet, a water world teeming with life is the most likely explanation for the measurement, says research leader Nikku Madhusudhan. But of course, it is essential to collect more data now to actually confirm this. The work is now nothing more than a starting point. It is important to remain deeply skeptical. But he can imagine that people will look back on this moment decades from now and realize that it has brought the “living universe” within reach. The discovery is presented in The Astrophysical Journal Letters.
Water worlds such as K2-18 b have long been considered the most promising candidates when it comes to the search for extraterrestrial life. They are now referred to as “hypocenic planets”, a mixture of the English terms for hydrogen (“hydrogen”) and (“ocean”). They are usually larger and hotter than the Earth and offer the best conditions for the development of microbiological life as we know it. Traces of these can be detected when they pass in front of their star from Earth's perspective, and instruments such as the JWST can analyze the composition of their atmosphere using starlight. This was probably crowned successfully.
(mho)
