Astrobiologists have used the term for many decades. This shell encompasses the distance at which a planet in a fairly circular orbit could maintain liquid water on its surface.
Bill Nye, among others, has speculated that "We May Discover Life on Europa."
With the landing of a probe on comet 67P, excitement has centered on the idea that life arose in water carried here by comets.
Since there are so many planets in the galaxy and universe, it’s natural to assume that there must be other intelligent life forms out there.
We live in an exciting age when we can begin to answer one of the most profound questions of the ages.