Living on Earth, without a single other habitable world in eyeshot, can sometimes feel pretty lonely. But our isolation may be the cosmic exception. In fact, it’s possible that throughout the galaxy, life-bearing worlds usually come in pairs.
In the opening scene of Ridley Scott's Prometheus, an alien Engineer is seen seeding the Earth with life — an interesting suggestion as to how life emerged on this planet.
We usually think of asteroid impacts as harbingers of mass extinction, but they might be the reason life exists on our planet at all. It's possible for bacteria to hitch rides on rocks ejected by space impacts and move from planet to planet. We know that certain Earth bacteria are capable of surviving the hostile…