Scientists have discovered new but preliminary evidence that a distant planet around another star could harbor life.
Planet K2-18b Shows Signs of Life-Linked Molecules
A Cambridge team analyzing the atmosphere of a planet named K2-18b has seen evidence of molecules which on our planet are only formed by simple life.
It is the second, and more hopeful, occasion chemicals linked to life have been seen in the planet’s atmosphere by Nasa‘s James Webb Space Telescope (JWST).
But independent astronomers and the team emphasize more evidence is necessary to verify these findings.
Lead researcher Prof Nikku Madhusudhan, who explained this to me in his laboratory at Cambridge University’s Institute of Astronomy, said that he hopes soon to get the clinching proof.
Planet K2-18b’s Distance and Size
“This is the strongest evidence yet there is possibly life out there. I can realistically say that we can confirm this signal within one to two years.”
K2-18b is half again as large as Earth and seven hundred trillion miles from us.
JWST is so capable that it can study the chemical makeup of the planet’s atmosphere from the light transmitted through from the tiny red Sun it orbits.
Life-Linked Gases Found: DMS and DMDS
The Cambridge team has discovered that the atmosphere appears to have the chemical fingerprint of at least one of two molecules linked to life: dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). On our planet, these gases are emitted by marine phytoplankton and bacteria.
Prof Madhusudhan explained that he was amazed at how much gas was seemingly detected in a single observation window.
“The amount we estimate of this gas in the atmosphere is thousands of times higher than what we have on Earth,” he said.
“So, if the association with life is real, then this planet will be teeming with life,” he told me.
Prof Madhusudhan went further: “If we confirm that there is life on k2-18b it should basically confirm that life is very common in the galaxy”.
Scientific Standards for Discovery
There are plenty of “ifs” and “buts” here, as Prof Madhusudhan’s team openly acknowledges.
First, this most recent detection is not up to the standard for claiming a discovery.
For that, the scientists must be on the order of 99.99999% confident that their findings are true and not a one-off fluke reading. In scientific terms that is a five sigma result.
These new results are only three sigma, 99.7%. Which sounds like a lot, but not quite enough to persuade the scientific community to take it seriously. But much greater than the one sigma result of 68% that the team achieved 18 months ago, and which was met with widespread scepticism then.
Even Five Sigma May Not Be Enough
But even if the Cambridge team records a five sigma result, that will not be proof that life is present on the planet, says Prof Catherine Heymans of Edinburgh University and Scotland’s Astronomer Royal, who is not part of the research team.
“Even with that certainty, there is still the question of what is the origin of this gas,” she told.
“On Earth it is produced by microorganisms in the ocean, but even with perfect data we can’t say for sure that this is of a biological origin on an alien world because loads of strange things happen in in the Universe and we don’t know what other geological activity could be happening on this planet that might produce the molecules.”
That interpretation is one that the Cambridge team concur in; they are collaborating with other teams to determine whether or not DMS and DMDS can be synthesized by non-living processes in the laboratory.
Competing Theories and Planet Structure Debate
There have been alternative, lifeless, explanations offered by other research teams for the data that have been collected from K2-18b. There is intense scientific controversy not just over whether DMS and DMDS exist, but also over the makeup of the planet.
The reason why many scientists conclude the planet is home to a massive liquid ocean is that the gas ammonia is not present in K2-18b’s atmosphere. Their assumption is that the ammonia is being consumed by a massive sea of water below. It could, however, be explained by an ocean of molten rock, which would rule out life, says Prof Oliver Shorttle of Cambridge University.
Studying the Faintest Signals
“Everything we know about planets orbiting other stars comes from the tiny amounts of light that glance off their atmospheres. So it is an incredibly tenuous signal that we are having to read, not only for signs of life, but everything else.
“With K2-18b part of the scientific debate is still about the structure of the planet,” he said.
Dr Nicolas Wogan of Nasa’s Ames Research Center has another explanation of the findings. He authored a study that indicated K2-18b is a mini gas giant without a surface.
Both these competing explanations have also been questioned by other teams on the basis that they are at odds with the observations from JWST, and this underlines the intense scientific controversy over K2-18b.
A Potential Turning Point in the Search for Life
Prof Madhusudhan admits there is still a scientific mountain to be climbed if he is to respond to one of the greatest questions in science. But he feels he and his team are on the right path.
“Decades from now, we may look back at this point in time and recognise it was when the living universe came within reach,” he said.
“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.”
The research has been published in The Astrophysical Journal Letters.