It is too early, much too early, to say we are not alone in this universe. But the discovery of evidence suggesting the strong possibility of life on another planet is undoubtedly, as Cambridge University astronomer Nikku Madhusudhan says, “a revolutionary moment … the first time humanity has seen potential biosignatures on a habitable planet.”
Observation of the atmosphere of the planet K2-18b, 124 light years away, by the James Webb space telescope has found traces of two chemicals, dimethyl sulfide (DMS) and dimethyl disulfide (DMDS), which are only known to be produced by life. On Earth in the oceans, for instance, certain forms of algae and marine phytoplankton produce the compounds, which waft into the air and add to the sea’s distinctive odour.
The best explanation for his group’s findings, published this week in The Astrophysical Journal Letters, Dr Madhusudhan says, is that K2-18b is covered with a warm ocean, brimming with life.
It is not, however, the only possible explanation and research on other potential sources for the chemicals and the composition of K2-18b continues.
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“It is in no one’s interest to claim prematurely that we have detected life,” he counsels, while we are also only at this stage discussing microbial life, very far down the evolutionary ladder from fish or intelligent life.
The search for evidence of extraterrestrial life although initially confined to the solar system, has, since the discovery in 1992 of planets orbiting distant stars, targeted those of the 6,000 identified “exoplanets” that are capable of supporting liquid water, thought to be essential for life.
K2-18b is 8.6 times as massive as Earth and orbits a red dwarf star smaller and less luminous than our sun, in the constellation Leo. It is too small to be observed directly by telescope but the illumination of its atmosphere as it passes in front of its sun allows spectral analysis of its composition.
It provides a tantalising hint at what may one day be proof that we are neither alone nor unique.
