Planets around double stars could boast life-friendly moons
Researchers in the new study were particularly interested in the newfound Kepler planets
New research suggests that planets orbiting pairs of stars could hold on to their moons, creating sites for life to evolve. Double-star systems can create a challenge in stability that their single-star cousins avoid, however. In both systems the stars move around slightly, potentially disturbing any orbiting planets and their moons. When two stars are dancing together it increases the odds that the stars will knock away a planet, as well as its moon.
"Stability is the first requirement for habitability,"
Adrian Hamers, a planetary theorist at the Institute for Advanced Study in Princeton, New Jersey, explains.
With his colleagues, Hamers modelled the stability of the ten confirmed exoplanets orbiting binary stars that have been identified by NASA's Kepler Space Telescope.
The researchers calculated the regions of stability where exomoons could be detected using future instruments.
"If the orbit of the exomoon is not stable then, in extreme cases, it will be flung out of the system," Hamers says.
While exomoons of planets that orbit a single star are a well-studied phenomenon, Hamers says, less work has been done for exomoons in binary systems. Circumbinary worlds have been discovered using other telescopes, but the researchers in the new study were particularly interested in the newfound Kepler planets. "We were curious which orbits of exomoons around these circumbinary planets would be dynamically stable," Hamers says.
The scientists ran multiple simulations of the moons of planets around stellar pairs. Results showed that stable simulated moons remained close to their planets, at about 0.01 AU (1 AU being the Earth-Sun distance) apart, so that these moons were less affected by the gravity of the stellar pairs. Moons were also more stable when they circled more massive planets. The angle of the moon's path around the planet compared to the planet's path around the suns proved important as well. When a moon circled at a 90-degree angle compared to the planetary path the moon oscillated widely before becoming unstable, crashing into the planet or, on rare occasions, one of the stars.