The human mind has had an innate desire to understand our place in the universe. This curiosity has driven us to search for evidence of life beyond Earth and has helped us find various types of planets beyond our solar system - rocky planets, gaseous planets, super-Earths, hot Jupiters and so much more.
What are Hycean worlds?
On August 26, 2021, a group of astronomers, Nikku Madhusudhan, Anjali A. A. Piette, Savvas Constantinou, from the Cambridge's Institute of Astronomy identified a new class of habitable planets called ‘Hycean Planets’ (Hy- from Hydrogen and -cean from Ocean) composed of water-rich interiors with massive oceans, high temperatures and Hydrogen-rich atmospheres.
They are found to have densities between those of rocky super-Earths and more extended mini-Neptunes, thus, making them optimal candidates in the search for exoplanetary habitability.
Astronomers have classified K2-18 b and TOI-270 d as Hycean planets.
What is the Structure of Hycean Planets?
The internal structure model for the Hycean planets created by Madhusudhan and his team is based on one of the candidates, K2-18b. The model comprises an iron (Fe) inner core, a rocky (silicate) outer core, a water layer, and a hydrogen/helium-rich atmosphere. These planets may sometimes be tidally locked. That means, the planet rotates in such a way that only one side faces the star. For a tidally locked planet, there is no day or night, only freezing darkness on one side and burning constant sunlight on the other.
Different Types of Hycean Planets
There are 3 types of Hycean planets –
Regular Hyceans - These have both dayside and nightside habitability with equilibrium temperatures being 210–430 K.
Dark Hyceans - These are tidally-locked planets and have temperatures as high as 510 K. Having no incident irradiation from the host star, their energy source is the energy redistributed from the day side through atmospheric circulation and internal energy. Planets like these, with high temperatures and inefficient energy redistribution, can have significant day–night temperature contrasts, and the nightsides of such planets may be habitable resulting in a possibility for nocturnal life.
Cold Hyceans - These Hyceans have very large orbital separations and thus have no stellar irradiation due to which the only source of energy is internal heat. The surface would be frozen but subsurface ocean life could still be possible.
In conclusion, Hycean planets are a type of habitable planet described as a hot, water-covered planet with a hydrogen-rich atmosphere that could bear life. Moreover, the habitable zone of such planets could be considerably larger than that of “Earth-like planets” Additionally, there could be tidally locked “Dark Hycean” (habitable only on the permanent nightside) or “Cold Hycean” (negligible irradiation). Hycean worlds could soon be investigated for biosignatures by terrestrial telescopes and space telescopes like the James Webb Space Telescope.
Comments