HOW WILL WE FIND OUT WHETHER EXOPLANETS ARE INHABITED?

Since we have only one example of life – what’s found here on Earth – we have no choice but to look for ‘life as we know it’. And all life on Earth requires water. This has given rise to the idea of a star’s habitable zone. A planet orbiting within this region is close enough to its star that water does not freeze and far enough away that it does not boil. This not-too-cold, not-too-hot ‘Goldilocks zone’ is quite narrow around the huge majority of stars, which are red dwarfs, but wider around Sun-like stars.

Recently, the concept of the habitable zone has been considerably widened. This is because of the discovery of ice- covered oceans located on Jupiter’s moon Europa and Saturn’s moon Enceladus. Although they intercept so little light that they should be frozen solid, they are heated by tidal stretching and squeezing from their parent planets. There is also the possibility that a planet orbiting far from its star might be kept warm by radioactive heat from its own rocks if it is swaddled in a blanket of greenhouse gases.

Life, it seems, might survive in environments far removed from those on Earth.