The majority of stars in the galaxy are locked in an orbital dance with at least one stellar companion. We now know that planets around such stars are very common, raising the question of how of how common life may be in such cases. To help resolve this astrophysicists have released an online tool for calculating the location of the habitable zone for a planet orbiting a star that is part of a binary system.
Professor Manfred Cuntz of the University of Texas, Arlington, has set out to model the influences on planets in such situations in a more systematic manner than has been done before. "The challenge is to properly consider two separate criteria consisting in the amounts of stellar radiation, which provides a favorable planetary climate for life, and the gravitational influence of both stars on an existing planet,"
Double star systems are classified as P-type, where the stars are close enough to each other that the planet orbits around both and S-type where the planet orbits one star. Cuntz has modeled both, with his work to be published in The Astrophysical Journal, but pre-released here on arXiv.
Unsurprisingly, Cuntz finds that more eccentric (stretched out) orbits are less likely to produce habitable zones, since such a path is likely to either fry or freeze the planet at some point. (Sorry Helliconia fans). Many relative planetary and stellar distances proved unstable, destroying the prospects for habitation. Nevertheless, Cuntz says, “Habitability is identified for a considerable set of system parameters.”
Anyone discovering a planet in a binary system and pondering the prospect of life can use Cuntz's calculator BinHab by feeding in data on the stars' brightness and mass along with the planetary orbital characteristics. Science fiction writers wishing to keep their planets credible may also find it useful. The work has already proven relevant to Kepler-16, a binary system with a P-type planet the size of Saturn, which could have habitable moons.
