Half-Frozen Half-Scorched Worlds

Red dwarf stars are by far the most abundant stars in the galaxy. A terrestrial planet orbiting in the habitable zone of a red dwarf star is expected to be tidally-locked with one side of the planet permanently facing the star. This is because a red dwarf star is much dimmer than the Sun and a planet has to orbit much nearer to it in order to receive sufficient warmth for liquid water to exist on its surface. Being so close to its parent star, tidal evolution quickly causes the planet to become tidally-locked with one hemisphere of the planet permanently pointed towards the red dwarf star, just like the same hemisphere of the Moon always faces the Earth. The outcome of this is a permanent dayside and permanent nightside on the planet.Figure 1: Habitable zone of the Sun compared to the habitable zone around Gliese 581 - a red dwarf star known to have planets around it.Figure 2: A tidally-locked planet with a frozen nightside and a scorched dayside. This planet is located in a star system consisting 2 or more stars since part of the planet’s nightside is faintly illuminated by light from a more distant star in ...