A super-Earth planet that dips in and out of its star's habitable zone has been discovered just 19.7 light-years away.
The planet, known as HD 20794d, gets farther out from its star than Mars is from the sun and, on the other end of its orbit, as close as Venus. Each orbit the planet begins out beyond the habitable zone, where it is too cold for liquid water, before passing right through the habitable zone to its inner edge where temperatures rise for a short period, before the planet moves back out again.
