Scientists find potential biosignatures in faraway exoplanet. What does this discovery mean for extraterrestrial life?

But he clarified that the results did not amount to discovering extraterrestrial life. “It is in no one’s interest to claim prematurely that we have detected life,” he said.

An interesting planet

A team of researchers from the University of Cambridge that has been studying data from the planet K2-18b, some 120 light years away from Earth, has reported strong signals of dimethyl sulphide (DMS) and dimethyl disulphide (DMDS), the first time these gases have been detected outside the solar system.

On Earth, these are a products of metabolic processes and the decay of small plant-like organisms in the oceans. This has led to scientists hypothesising on the possibility of a warm ocean on K2-18b, an environment similar to the one that gave rise to life on Earth about 3.5 to 4 billion years ago.

Since its discovery in 2015, K2-18b has generated a lot of interest among those searching for extraterrestrial life. It is about nine times as heavy as Earth, and moves around a star that is smaller and cooler than the Sun. Notably, K2-18b lies in the so-called “habitable zone”: the region around a star where water can remain in liquid form.

In 2019, data from the Hubble Telescope had detected signals of the presence of water vapour in K2-18b’s atmosphere. Two years ago, the same team that reported the latest findings based on data collected by the James Webb Space Telescope, presented evidence for the presence of methane and carbon dioxide, also signs of possible life on the planet.

They had even detected hints of DMS at the time, although the latest evidence is much stronger.

Only indications, no evidence

The mere presence of certain gases on other planets, even though linked to life processes on Earth, do not necessarily provide definitive evidence of life. They simply make the celestial body an interesting subject of scientific research.

Madhusudhan did not rule out the possibility that the DMS found in the atmosphere of K2-18b could be the product of processes that humans are unaware of. “While DMS is known to be a robust biomarker, there is always a possibility that we may not have accounted for some physics or chemical process that we do not know of,” he said.

The presence of water, considered essential for life as we know it, on any celestial body also generates similar excitement. It has been found, in different states, in several places within and beyond the solar system. But none of them, as far as we know, support life.

In fact, Mars, Venus and some other planets outside the solar system have at different times offered signals indicating the presence of certain gases, which keeps the scientific community excited about the possibility that they support life.

A statistical argument

But the lack of evidence does not rule out the possibility of extraterrestrial life either. Our active search for life beyond Earth is only decades old. Today, there is a new field of study, called astrobiology, dedicated to looking for signals of life in extraterrestrial spaces.

In the absence of any evidence, however, the strongest argument for the presence of life beyond Earth comes from statistics. Even if the origin of life on Earth was a one- in-a-billion event, there are just so many planets in the universe — trillions, according to our current understanding — that similar life-generating accidents must happen, statistically speaking, at thousands or even millions of other places. And at least some of these might happen near enough to Earth to be detected by humans.

This line of argument has even given rise to the Drake equation, named after astronomer Frank Drake, that seeks to estimate the number of potential extraterrestrial civilisations within our own galaxy, with whom humans are within a communicable distance.

The calculation is dependent on information such as the average rate of star formation in our galaxy, the fraction of the stars that have planets, average number of habitable planets around every star, the fraction of such planets where life actually originates, and the fraction of life that becomes intelligent enough to communicate.

Considering the large uncertainties in most of these factors, the equation can spit out a result that can range from less than one, meaning Earth is the only place with life, to millions. And with new data, the Drake equation continues to evolve.

It is thus not a scientific fact, but simply a tool used to assess the statistical probability of finding intelligent life beyond Earth.