Hot Jupiters prefer to go it alone

Eventually, the star pulls the larger planet into a tight circular orbit This theory suggests a close encounter between two large gaseous planets early in the solar system's formation, forcing one to be flung out of the solar system, and the other into a highly elliptical orbit. Using data collected by NASA's Kepler space telescope, a team of researchers led by Dr Jason Steffen, of the Fermilab Center for Particle Astrophysics in Illinois, examined 63 stars that are known to have hot Jupiters to see if they had smaller planets orbiting alongside. The finding, published in the Proceedings of the National Academy of Sciences, also confirms the chaotic path these planets take to end up close to their parent star. The team also looked at a number of stars with 'warm Jupiters' - large planets that orbit their star once every two weeks - and 'hot Neptunes' - close orbiting mid-sized planets. Until recently, most scientists believed that these large planets slowly migrated in towards their star, pushing smaller planets in with them. Astronomers searching for Earth-like planets can strike off stars that have a 'hot Jupiter' orbiting around them, according to a new study. If the remaining planet passes close to any smaller planets that have formed around the star, it also flings them out of the solar system. "If you have a [previously] measured planet, which in this case is a hot Jupiter, you can look for deviations that result from gravitational interactions with other planets in the same system," says Steffen. They detected the presence of Earth-like planets around approximately 10 per cent of the warm Jupiter systems, and 30 per cent of the hot Neptune systems. Their analysis failed to find any. Hot Jupiters are large gaseous planets that take less than a week to complete one orbit. Chaotic beginnings.

Steffen says the absence of smaller rocky planets alongside hot Jupiters confirms the planet-planet interaction theory and "puts the nails into the coffin" of the migration theory.

He says it also narrows down the number of solar systems astronomers need to focus on when looking for Earth-like planets.

"You're not going to find habitable Earths in these hot Jupiter systems," says Steffen. "There's a lot of value in continuing to monitoring them, but it's for other reasons now."