Not all that long ago we assumed habitable planets needed a star
like our Sun to thrive, but that view has continued to evolve.
M-class red dwarfs may account for as many as 80 percent of the
stars in our galaxy, making habitable worlds potentially more
numerous around them than anywhere. And let’s extend our notion
of habitability to what Luca Fossati (The Open University, UK)
and colleagues call a Continuous Habitable Zone (CHZ). Now
things really get interesting, for a red dwarf evolves slowly,
so planets could have a CHZ with surface water for billions of
years. But what about white dwarfs? Stellar evolution seems to
rule out habitable worlds around them because we normally think
of stars entering their red giant phase and destroying their
inner planets enroute to becoming a white dwarf. But can a new
planetary system emerge from the wreckage? We’ve already found
planets orbiting close to the exposed core of a red giant (KOI
55.01 and KOI 55.02), showing that the end of main sequence
evolution isn’t neces