One of the major questions vexing modern science is whether there is life elsewhere in the universe. While no direct evidence of such life has been discovered, exoplanet-hunting missions like Kepler have changed many of our ideas about how planetary systems are formed and have provided scientists with the means to think about life beyond our solar system without leaning so heavily on conjecture and speculation.

Out of the more than 4,000 exoplanets found so far, a number have been deemed to be habitable, though this is a somewhat misleading term. It doesn't mean a planet where one could land and start homesteading. It means a rocky planet that is in the right orbital region around its star where the temperature is moderate enough for liquid water to exist on its surface without freezing or boiling away. To give an idea of how generous this is, Earth is habitable under these criteria, but so are Venus and Mars, which are scarcely garden spots.