Cambridge scientists have discovered with 99.7% accuracy gases on a distant planet, K2-18b, that are indicative of life. While this is the strongest evidence ever of life beyond earth, the discovery needs to go through several scientific checks before any conclusion can be reached. Ivinder Gill explains how it is a tipping point for research on extra-terrestrial life
Why the excitement
NASA’s James Webb Space Telescope (JWST) has discovered molecules of dimethyl sulphide and dimethyl disulphide — gases produced only by living organisms as far as human knowledge goes — in the atmosphere of planet K2-18b at a concentration thousand times higher than on earth. This suggests that the planet may have oceans teeming with life. The discovery was made by a group of scientists at Cambridge University’s Institute of Astronomy, led by Nikku Madhusudhan. Calling the discovery astounding, Madhusudhan told the media: “These are the first hints we are seeing of an alien world that is possibly inhabited. This is a revolutionary moment.”
What is K2-18b?
K2-18B IS A planet 700 trillion miles away from us orbiting a cool dwarf star in the constellation of Leo. About two and a half times the size of Earth, it is at a distance from its star where temperatures are neither too hot nor too cold, and can harbour liquid water and, possibly, life. Scientists have suggested it is completely covered by a deep ocean, with an atmosphere rich in hydrogen. Initial studies of the planet revealed methane and carbon dioxide in its atmosphere, with weak hints of dimethyl sulphide. But the latest data shows a very strong signal for both dimethyl sulphide and dimethyl disulphide. Madhusudhan said his team spent months testing the signal and even “trying to get rid of it”, but it persisted, making them sit up.
Other planets with possibility of life
The Kepler Space Observatory Mission team has estimated that there are at least 50 billion planets in the Milky Way, of which at least 500 million are in the habitable zone. And not just planets, moons also can be habitats for life. Within our solar system, Mars, Jupiter’s moon Europa, and Saturn’s moon Enceladus are possible candidates for living organisms. Mars is known to have had liquid water on its surface in the past, and has subsurface reservoirs as well. Europa and Enceladus also are believed to have oceans that could harbour life. The conditions for life as we know it include liquid water as a fundamental requirement, carbon-based molecules, and a source of energy — such as a star or tidal forces — which can maintain life. However, no evidence has so far has been found of life elsewhere, with K2-18b being the most promising discovery yet.
How promising is the discovery?
This is the strongest evidence ever of life outside earth, but not a confirmation by any means. For a discovery to be correct and not just a coincidence, a 99.99999% accuracy is needed, known as a five sigma in scientific terms. The Cambride team’s discovery is a three sigma, at 99.7%. This is significantly higher than the previous best indicator of life the same team got about 18 months back, at a one sigma result of 68%. While Madhusudhan claims he can confirm this signal within one to two years, there is considerable scepticism too.
Foremost is the origin of the two gases. We know they can only be produced by plankton and bacteria, but in a mysterious universe, anything is possible, and these gases could have a non-biological source too. The team’s first task would be to ascertain if these gases can be produced in a lab. There are also doubts over K2-18b’s composition, with some theories proposing it has a vast ocean of molten rock which would preclude life. Another theory is that the planet is a mini gas giant with no surface. However, both theories are inconsistent with data from JWST. With the data to be made public, it will be open to other scientists too for their study.
For now, Madhusudhan believes he is on the right track to answering one of the most important questions in science. “This could be the tipping point, where suddenly the fundamental question of whether we’re alone in the universe is one we’re capable of answering,” he said.
More research on extra-terrestrial life
With powerful equipment like JWST, scientists can analyse the chemical make-up of planets’ atmospheres to search for signs of life. As more planets are studied, the list of likely planets with life will also grow. Scientists say this observational data will lead them to explore the universe like never before, substantiating data with theory and laboratory work. Some others believe that instead of atmospheric signals, technosignatures, or intercepted message from an advanced civilisation, are more sure signs of life. However, despite several conspiracy theories about UFOs and alien sightings, and scores of creative interpretations of extra-terrestrials in films or TV, the likelihood of receiving such a signal is remote. Most importantly, whether the laws of biology are universal in nature, is a question that nobody can answer. Yet.