Astronomers at the University of Cambridge (UK) have identified a new class of exoplanets that are very different from ours, but which could also host life, vastly expanding the list of places to look for it outside the solar system. They have been called Homo worlds‘(Hycean worlds, in English), as published in The Astrophysical Journal.
The main author, Nikku madhusudhan, explains to SINC the characteristics that a planet of this type must meet: “Present a surface covered by ocean and one atmosphere dominated by hydrogen (H2) – hence its name -, with a pressure and temperature on the oceanic surface conducive to life, that is, within the limits of the habitability conditions of the Earth’s oceans. ”
These worlds have a surface covered by the ocean, an atmosphere rich in hydrogen, and a pressure and temperature on their surface conducive to life.
– University of Cambridge
Although they are planets larger and hotter than ours, “we assume that at least one microbial life similar to that found in the terrestrial oceans (even in extreme conditions), it should be able to originate and adapt to the haeanic conditions “, adds the astrophysicist.
So far, signs of life have been sought on planets with similar size, mass, temperature and atmospheric composition to Earth, but they are not easy to find. However, according to the authors, ‘doanic’ worlds are more numerous and easier to observe.
In addition, they are positioned in much larger living areas than those of the terrestrial ones. This means that they could support life even though they are outside the range in which a planet similar to ours would need to be to be habitable.
“We have identified 11 candidate exoplanets of this class (K2-18 b, TOI-1266 c, LTT 1445 Ab …) around nearby stars. Therefore, it is evident that there could be dozens more in the entire population of exoplanets discovered, “says Madhusudhan, who insists:” a completely new path opens in the search for life elsewhere.
All identified planets of this class orbit red dwarfs that are between 35 and 150 light years apart, that is, very close from an astronomical point of view.
Biofirms in your atmosphere
In the search for signs of life on distant extrasolar planets it is essential to find ‘biosignatures‘or possible molecules of biological origin in their atmospheres. The most common are oxygen, ozone, methane, and nitrous oxide, all of which are present on Earth.
But there are other biomarkers that are less abundant on our planet but in exoplanetary atmospheres rich in hydrogen. “In the ‘doanic’ worlds there may be methyl chloride, dimethyl sulfide, and carbonyl sulfide, molecules all of them considered as possible biosignals in planets similar to Earth “, points out the Cambridge astrophysicist.
Methyl chloride and dimethyl sulfide may be present in the atmospheres of the ‘Hanic’ worlds, biosignatures that could be detected by the James Webb Space Telescope.
His team trusts that James Webb Space Telescope (JWST) -whose launching is due this fall – he can detect them with relative ease, and considers finding biosignatures of life outside our solar system in the next two to three years to be a real possibility. “Detecting a biosignal would transform our understanding of life in the universe, “emphasizes Madhusudhan.
The track of the minineptunes
Of the more than 4,000 exoplanets discovered so far, the vast majority are between Earth and Neptune in size. In fact, they are often called “supertierras” or “minineptunos“: They can be predominantly rocky or ice giants with hydrogen-rich atmospheres, or something in between.
Most minineptunes are 1.6 times larger than Earth. Previous studies have concluded that the pressure and temperature under their hydrogenated atmospheres are too high to support life.
There may also be ‘dark doanic worlds’ with habitable conditions only on their permanent night face, and ‘cold doin worlds’ that receive little radiation from their stars.
However, a recent study by Madhusudhan’s team on the minineptune K2-18b – one of the eleven identified ‘haitanic’ worlds – revealed that they could support life under certain conditions.
This led to the investigation and identification of the ‘Hatanic’ planets. They may be up to 2.6 times larger than Earth and have atmospheric temperatures of up to almost 200 ºC, but their oceanic conditions could be similar to those that support microbial life in our oceans.
These planets include ‘dark hician worlds’ which, blocked by tidal gravitational forces, could have habitable conditions only on their permanent night faces, as well as ‘cold doanic worlds‘that receive little radiation from their stars.
Exoplanets with the size of these worlds are the most abundant, so to confirm that they belong to the class ‘hadanic’ other parameters such as mass, temperature and their atmospheric properties would be needed.
These data are still unknown on many exoplanets, but the JWST and other telescopes will reveal them in the coming years. Signs of life could soon be discovered on any of these worlds.