There is a new type of exoplanets on which to try to search for life forms

There is a new type of exoplanets on which to try to search for life forms

According to a group of astrophysicists, the Hycean planets, very different from Earth, however, have characteristics that could be compatible with extreme life forms

(image: Guillem Anglada-Escude - IEEC / Science-wave, SpaceEngine. org) They are called "Hycean" planets and are said to be extrasolar worlds very, very different from the Earth and the rocky planets, the only ones on which the search for alien life has so far focused. Yet, according to Nikku Madhusudhan and his team at the University of Cambridge's Institute of Astronomy, they should be the next to end up in the lenses of scientists' telescopes because they could be hiding microorganisms similar to our extremophiles, those who live in extreme environmental conditions on Earth. . The research was published in the Astrophysical Journal.

The Hycean planets

The Cambridge team defines the Hycean planets (a term that comes from the fusion of the words hydrogen, i.e. hydrogen, and ocean , ocean) as worlds up to 2.6 times the size of the Earth, with a mass up to 10 times greater. In practice, they would be comparable in size to the rocky "super-Earths" but with characteristics close to gaseous "mini-Neptune". They are planets with an atmosphere rich in molecular hydrogen below which there could be vast oceans.

This type of exoplanets could be quite widespread outside our solar system, but until now it has been excluded from the search for alien life because it is believed that it does not offer conditions compatible with the survival of any organism. In fact, some Hycean planets would be very close to their star (with atmospheric temperatures that can reach 200 ° C) and others far away to such an extent that they cannot receive the necessary energy.

Extreme life

For Madhusudhan and colleagues, however, things could be different. Scientists support the hypothesis that, precisely because of their characteristics, the habitable zone of the Hycean planets would be much larger than that valid for the rocky Earth-like planets.

Within certain parameters, therefore , even on some Hyceans life forms could develop, perhaps similar to our extremophilic microorganisms. The so-called dark Hycean planets are those close to the star and have one face that is always illuminated and one that is always in the dark. Here life could exist right on the night side, farthest from the heat and radiation of the star.

Cold Hycean worlds, on the other hand, are those far away from their sun (which if they were rocky would be outside the habitable zone because completely frozen). Even if they receive little energy, Madhusdhan commented, “the greenhouse effect due to molecular hydrogen is such that the planet can be very far from the star and still have warm habitable conditions on the surface”.

In search of bio-signatures

"My guess is that this will be a paradigm shift in the search for life on exoplanets," Madhusudhan told Inverse: "We hadn't even considered planets like these as good candidates for life" .

The work of the next few years for scientists will therefore be to identify the Hycean planets near us and thanks to new generation telescopes such as the James Webb Telescope (whose launch is expected by the end of 2021) studying their atmosphere in search of biological signatures, that is chemical compounds that can be signs of life: ozone, oxygen and methane, but also methyl chloride and methyl sulphide. "When we looked for these various molecular signatures, we focused on Earth-like planets, which is a reasonable starting point," Madhusudhan explained. "But we think the Hycean planets offer a better chance of finding different traces of bio-signatures."

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