‘Goldilocks’ planets might not be so nice

What does ‘habitable’ really mean?

This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface. Credit: ESO / M. Kornmesser