There is no greater question in astronomy than its most basic: Are we alone?
Earth has all the ingredients needed for life; a warm, temperate climate, a substantial atmosphere of friendly gases, a healthy magnetic field, and — most importantly — liquid water.
Even though we've found more than 5000 exoplanets (that is, planets orbiting other stars), the hunt for a planet like ours remains elusive.
Or is it?
There are some captivating candidates, like Kepler-452b, which orbits a strikingly similar distance from its strikingly similar star. It is a super-Earth, with five times the mass and about twice the gravity.
We know nothing of its atmosphere — if it even has one — but there are other candidates that could be habitable, including one right on our celestial doorstep.