This sounds like good news for anyone hoping to spot alien life forms.
They could exist on a much larger number of planets than on those which held the attention of the researchers until now, ie the planets "twin" of the Earth.
A team of researchers from the University of Cambridge defined a new category of worlds that could be habitable, called "Hycean" planets, in an article accepted on August 26 by the Astrophysical Journal.
Already eleven "candidate" planets
These have nothing to do with Earth.
These exoplanets - that is to say outside our solar system - are rather super-Earths or mini-Neptunes, that is to say that they can be more than twice the size of the Earth. , but less than four times, as is the case with Neptune.
In addition, a "Hycean" planet would be covered with water, endowed with an atmosphere full of hydrogen and the temperature on its surface "would be within the limit of what is considered acceptable on Earth for life forms", summarizes Nikku Madhusudhan, astrophysicist at the University of Cambridge and main author of the article on these planets, interviewed by France 24.
"We have found eleven candidate planets 'Hycean' which are several tens of light years from here and which seem to us to be very suitable worlds for looking for biological signatures," he adds.
For the authors of this study, the existence of potentially habitable "Hycean" worlds considerably widens the field of possibilities in the discovery of traces of extraterrestrial life.
There are, in fact, far fewer Earth-sized planets in the universe than larger stars like these mini-Neptunes.
Additionally, smaller planets - like ours - have much weaker atmospheric signatures than larger ones, which "makes it easier to detect life forms on 'Hycean' type worlds," says Nikku Madhusudhan.
"If these planets are inhabited, we will be able to have the first records of biological signatures in only two or three years", ignites the Cambridge astrophysicist.
This will be thanks to the James Webb space telescope, which is due to be commissioned this year "and will be able to easily probe the atmosphere of these eleven candidate planets", concludes Nikku Madhusudhan.
K2-18b, exoplanet of discord
But let the alien hunters moderate their hopes.
The conclusions of the Cambridge researchers are far from unanimous.
"We do not know if planets as described in this article really exist. For the moment, it is purely theoretical", affirms Martin Turbet, astrophysicist at the astronomical observatory of Geneva, contacted by France 24.
All the scientific imbroglio goes back to the starting point of the hypothesis of habitable "Hycean" planets. It is an exoplanet called K2-18b, located about 124 light years from Earth. Nikku Madhusudhan's team estimates, in a previous article published a year and a half ago, that this mini-Neptune could well have all the required conditions: large amounts of water, an atmosphere rich in hydrogen and an acceptable temperature. for life on its surface.
K2-18b then becomes the mother of the family of "Hycean" planets.
"From our research on K2-18b, we established a model that allowed us to calculate the conditions necessary for planets with a hydrogen-rich atmosphere to be habitable," explains the Cambridge scientist.
Except that Nikku Madhusudhan is a bit alone in finding that K2-18b could be habitable.
"We never succeeded in reproducing the calculations which allowed him to reach his conclusion", affirms Jérémy Leconte, astrophysicist at the University of Bordeaux, contacted by France 24. The other scientists questioned by France 24 also confirmed have doubts about the model used by the Cambridge researcher.
Either way, there would be "something physically wrong with the idea of a planet at the right surface temperature, covered in water and with an atmosphere so rich in hydrogen", adds Olivier Mousis, astrophysicist at Aix-Marseille University.
He explains that in this type of world, there would be a lot of water that would evaporate in the atmosphere, thus generating a strong greenhouse effect that would greatly heat the surface of the planet.
"The temperature of the ocean would rise until the water becomes hypercorrosive, which is not a welcoming environment for life", summarizes Olivier Mousis.
So many criticisms that Nikku Madhusudhan rejects.
"I have nothing against scientists having other opinions, this is part of the necessary debate of ideas, but so far there have been no publications that have refuted our conclusions. in the end, that's what counts, isn't it? "says the Cambridge astrophysicist.
In the end, the James Webb space telescope will perhaps play the arbiter of this scientific quarrel, if it manages to detect traces of life on one of these planets.
And what would these life forms look like?
This is a point on which Nikku Madhusudhan and the other researchers interviewed by France 24 at least agree: we have no idea and anything is possible.
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