Sleepless aliens may be living on distant exoplanets with no daylight or seasons.
The Milky Way boasts between 100 billion and 400 billion stars. Of these, 70% are small, cool red dwarfs called M-dwarfs.
And they could hold the key to extraterrestrial lifeforms that parallel deep-sea and ground-dwelling creatures on Earth.
A 2013 study estimated that 41% of M-dwarf stars have a planet orbiting in their habitable zone, or the range of orbits with the right conditions for liquid water.
That means over 28 billion planets orbiting M-dwarfs could hold one of the keys to life - and that's not even considering other types of stars.
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