Exoplanet breakthrough: Sulphur traces hint at life beyond Earth

Is there life beyond Earth? A 99.7% probability is quite significant; however, for researchers to give a definitive answer, a probability of 99.99999% is necessary. According to Prof. Nikku Madhusudhan, who led the study of K2-18b's atmosphere, this could take up to two years.

Despite this unconfirmed but very high probability of discovering extraterrestrial life, it seems to fulfil Lisa Kaltenegger's predictions.

This is no coincidence. Thanks to tools like the James Webb Space Telescope, our ability to study the universe has increased to the point where it is highly probable that we might identify planets where life could have originated and survived.

On the list of potential habitats for cosmic life, alongside planets such as TRAPPIST-1e, is K2-18b. What exactly was found on it?

The compounds that have raised hopes in the scientific world are dimethyl sulphide and dimethyl disulphide, which on Earth are produced by bacteria and marine phytoplankton.

However, the enthusiasm of the discoverers is tempered by Prof. Catherine Heymans from the University of Edinburgh:

One of the assumptions made by researchers is the correlation between the existence of life and the presence of liquid water. It is assumed that while the mere presence of water in a liquid state does not guarantee the emergence of life, water is essential for life to arise and develop.

This significantly narrows the conditions under which, according to accepted assumptions, life in space might arise: the search is focused on exoplanets in the so-called habitable zone, which is the distance from a star where temperature and conditions allow for the existence of liquid water.

Exoplanets – planets outside the Solar System – hold great promise for science. Just 40 years ago, we didn't know of any, though many researchers suspected they might exist.

Doubts were dispelled by a Pole, Aleksander Wolszczan, who, along with Dale Frail, performed a second Copernican revolution in astronomy in 1992 by announcing the discovery of two planets (and a probable third) orbiting pulsar PSR 1257+12.

Since then, the list of discovered exoplanets has been rapidly growing. While there were over 2,000 known in 2017, by 2024, astronomers had identified over 7,000 planets outside our solar system. We can be sure that this number will continue to increase significantly each year.

About 1% to 2% of the discovered exoplanets may be in the "habitable zone," so the excitement among universe researchers is justified – already, the number of planets that may deserve the title "second Earth" reaches the dozens and will grow. And with it, the chance that there is life on one of them.

An attempt to interpret what this means was presented in the 1960s by the American astronomer Francis Drake, who formulated the so-called Drake Equation.

This formula considers the rate of star formation, the chances of forming planetary systems and life-supporting planets, as well as life’s evolution from simple to complex, and finally to intelligent forms capable of interplanetary communication.

The problem is that the Drake Equation – even when assuming the most pessimistic scenarios – yields 250,000 cosmic civilisations capable of making contact, yet no contact occurs.

This paradox, the statistically high probability of extraterrestrial life yet the lack of evidence for its existence until recently, was aptly summarised years ago by the Italian physicist Enrico Fermi. The famous Fermi Paradox can be reduced to the question: "Where are they?"

There could be many answers, and scientists' assumptions are translated into understandable and attractive language by pop culture.

An example is Liu Cixin, author of the bestseller "The Dark Forest." The dark forest theory suggests that the lack of contact is a survival strategy in a potentially hostile environment. The cosmos is full of intelligent life, but its representatives – precisely because they are smart – do not flaunt their existence.

This theory contrasts with humanity's current actions. NASA has already sent detailed information into space about the Blue Planet, its inhabitants, and how to locate Earth in the vast universe. A compendium of knowledge about Earth is carried on the discs by the two Voyager probes, and also, in a reduced form, on plates attached to the Pioneer 10 and Pioneer 11 probes.

There are also hypotheses that alien civilisations – if they exist – may be at such a high level of development that their attempts to communicate are invisible or incomprehensible to us. This was referenced by the Strugatsky brothers, who in "Roadside Picnic" put forth the idea that alien civilisations visit Earth regularly. Still, the remnants of their visits are as abstract and incomprehensible to Earthlings as the remnants of a picnic are to ants.

This line of research is being pursued by the SETI Institute, the University of California, Davis, and the Alaska Whale Foundation to communicate with humpback whales. Successful attempts at interspecies exchange of simple messages, confirmed in 2023, aim to lay the groundwork for potential future communication with extraterrestrial civilisation.

Especially since universe researchers, alongside analysing the geological structure and potential atmosphere composition of exoplanets, are also searching for more definite signals: radio communications, various emissions, brightness fluctuations, inexplicable disturbances in planet movements or the brightness of distant stars.

So far – despite decades of efforts, ambitious programmes like SETI, and the registration of inexplicable signals, such as the WOW Signal! – success has eluded us.

Therefore, the discovery of life on K2-18b could be groundbreaking. Maybe, because – it is worth remembering – researchers' integrity prevents them from making definitive claims, and the results obtained still require confirmation. We still have to wait to change the communication from "high probability" to the clear statement "we have discovered life beyond Earth."