Oceanic worlds with powerful atmospheres and hydrospheres are often considered good candidates for the search for life, especially if they are located near red dwarfs famous for their flares. However, a new study shows that their “habitable zones” may be even narrower than those of ordinary planets.
Oceanic planets
Oceanic, or, more precisely, hycean worlds are planets that are completely covered with many kilometers of water and in addition have a very dense atmosphere, which may predominantly consist of hydrogen. A recent study makes us take a fresh look at them.
A rather large super earth could turn into a hycean world. This assumption is based on the current theory of planet formation. True, there is nothing like that in the Solar System, so actually their existence is only an assumption.
However, scientists are hopeful that they are fairly widespread in the Universe. This is especially true for red dwarf systems. These small stars are characterized by powerful flares that over billions of years can rip the atmospheres off planets in their own habitable zone, turning potentially earth-like worlds into deserts.
But ocean worlds, with their powerful gas and water envelopes, can resist this process. In addition, the very concept of “habitable zone” is based on a very crude model in which the surface temperature is determined only by the heating of the star at a certain point in time. In reality, the effects of water and air have to be taken into account as well.
It’s not so simple
Hycean or oceanic worlds should have high thermal inertia and greenhouse effects. Therefore, it is believed that they will remain comfortable to live in even if they are on the outer limits of their habitable zones. And that’s where the authors of a new study have made their point.
They found that all previous calculations did not take into account tidal heating of the planet’s depths. This is a manifestation of the force that makes red dwarf planets rotate synchronously relative to their luminaries. But it not only slows down the rotation, it deforms them. And the mechanical energy of deformation is then converted into thermal energy.
How strong can this effect be? On Jupiter’s moons, which don’t get enough heat from the sun to melt the ice, it’s powerful enough that oceans exist beneath it. Therefore, on oceanic red dwarf worlds, it could definitely provide enough energy to trigger a greenhouse effect that would turn the planet into a vaporous hell.
That is, due to the tidal warming of oceanic worlds, their “habitable zones” are expected to shrink greatly from the interior, and this slightly reduces optimism about these worlds. The effect will depend on a bunch of factors: the mass of the world, the mass of the star, and the eccentricity of the orbit.
In any case, the extended atmospheres of hycean worlds make them desirable candidates for spectroscopic studies. It is quite possible that traces of life will be found even on those that look completely unpromising.
According to phys.org
