Binary systems have traditionally been considered hostile environments for the formation and survival of “Star Wars planets” like Tatooine… but it looks like “a new hope” could actually exist for them
I love science fiction, both books and movies. While I prefer Isaac Asimov’s universe, I have always loved Star Wars” adventures, starting with the great classics of the late 70s. “Star Wars: A new Hope” came out in 1977. It starts in the immediate vicinity of a very particular planet named Tatooine, with the characteristic of orbiting around a binary star. But can a planet actually form in a binary system? And if it can, how likely can it be habitable? Since stellar binarity is fairly common, with about half of all Sun-like stars having a stellar companion, binary stars could represent a large fraction of the stars with a planetary system. Nevertheless, binary systems have traditionally been considered hostile environments for the formation and survival of planets, often causing them to be excluded from programs aimed at the discovery of new planets. But recent discoveries have shown that planets can actually form and survive in the adverse environment of a binary star, thus motivating new interests in these objects.
But that’s not the whole story: Jerome A. Orosz (Astronomy Department, San Diego State University) et al. discovered the planetary system Kepler-47 using the Kepler space telescope in 2012. This is a system formed by two planets with radii equal to 3 and 4.6 times the Earth radius, orbiting around a binary star, with a primary mass comparable to the Sun and a secondary with a mass equal to about a third of a solar mass. But the most interesting aspect is that the outermost planet, with more than 4 times the Earth’s radius, orbits in the so-called “habitability zone”. This is the ideal distance from the stars to allow the existence of liquid water if it were a rocky planet like Earth! However, it seems like this planet is more similar to Uranus or Neptune. On the other hand, with this discovery Kepler demonstrated that even short-period binary systems can host planets, including planets in the habitable zone. It therefore seems that “Tatooine” may not be just science fiction …
References:
Orosz et al., 2012: “Kepler-47: A Transiting Circumbinary Multi-Planet System” https://arxiv.org/abs/1208.5489
