How do planets go into orbit

Observations confirm theoretical predictions - Earth's moon could have emerged from a similar constellation

Mountain View (USA) - Using the data from the Kepler Space Telescope, researchers have found more than a thousand possible exoplanets in the past four months, in some cases up to six planets are said to orbit a star. They made another interesting discovery in one system: apparently two planets share the same orbit. This observation supports the theory that the earth was once in the same orbit with another body that was responsible for the formation of our moon.

The KOI-730 system consists of four planets. Two of them orbit the central star at the same distance and take 9.8 days to complete one orbit. The distance between them corresponds to an angle of 60 degrees measured from the center of the star. It is precisely this arrangement that makes it possible for the pair not to collide. Astronomers also call the possible locations of several bodies in an orbit "libration" or "Lagrange points". There are five of them in total, but only positions at an angle of 60 degrees in front of or behind a planet guarantee a stable orbit. At Jupiter in our solar system, groups of asteroids, the so-called "Trojans", move in these two places.

"Systems like this are unusual, it's the only one we could discover," reports Jack Lissauer of NASA's Ames Research Center in California. Theories had already predicted that two planets could form on the same orbit. The further investigation of KOI-730 is difficult, however, because the associated star is only weakly glowing.

Researchers at Princeton University further examined the data from KOI-730 and calculated that the two planets can orbit for at least two million years without getting in each other's way. Our moon is said to have formed 50 million years after the formation of the solar system, after a Mars-sized body called Theia hit the earth. According to simulations, it must have approached at a low speed. It is therefore possible that Theia was also in orbit of the earth for a while.