Like Luke Skywalker's Home, Planets with Two Stars Likely Formed Far, Far Away

Circumbinary planets - where one planet orbits two stars - are an astronomical rarity that can only occur when the planet forms far away from its two parent stars and subsequently migrates into orbit with the binary system, according to new research published in Astrophysical Journal Letters.

Fans of the Star Wars franchise no doubt know that Luke Skywalker's home planet, Tatooine, has two suns. In the opening act of the space saga, Skywalker can be seen gazing at a double sunset from his desert home world.

If Tatooine were a real planet, it would have had to form far, far away from its parent stars, according to the new University of Bristol study, which utilized the Kepler Space Telescope to observe real life circumbinary planets.

One of the planets observed - Kepler-34 (AB)b - is nothing like Tatooine. It is a harsh and volatile word of extreme gravitational forces and destructive cosmic collisions.

"Our simulations show that the circumbinary disk is a hostile environment even for large, gravitationally strong objects. Taking into account data on collisions as well as the physical growth rate of planets, we found that Kepler 34(AB)b would have struggled to grow where we find it now," said Zoe Leinhardt of the University of Bristol.

Leinhardt and her colleagues ran computer simulations for the early stages of planet formation around binary stars that used a model that calculates the gravity and physical conditions of planetary building blocks.

Based on their simulations, the researchers suggests that Kepler-34 (AB)b and other circumbinary planets like it must have formed significantly farther away from their host stars than they are now. Of all the circumbinary systems they studies, only one, Kepler-47 (AB)c, could have possibly formed in its current position, but that planet has the most distant orbit of all the systems studied.

Circumbinary planets have captured the imagination of many science-fiction writers and film-makers - our research shows just how remarkable such planets are," said lead study author Stefan Lines. "Understanding more about where they form will assist future exoplanet discovery missions in the hunt for earth-like planets in binary star systems."