Astronomers have described the strange behavior of Pluto and its five moons in a paper published on Wednesday.

NASA’s New Horizon spacecraft will visit Pluto this summer, giving scientists new insight into its behavior and composition. However images from the Hubble Space Telescope have already allowed scientists to calculate how bizarrely the moons of the dwarf planet behave, writes Kenneth Chang for The New York Times.

Unusual Behaviour Of Pluto Moons Revealed

Chaotic orbits in a strange system

The miniature planetary system formed by Pluto and its five moons is unique in the solar system. One moon is so large relative to Pluto that some scientists classify Pluto and Charon as a double planet, because of the fact that the center of mass of the two lies outside Pluto.

Two other moons, named Nix and Hydra, were first seen in 2005 thanks to images from Hubble. The moon Kerberos was discovered in 2011, while Styx was announced in 2012.

Now two scientists have calculated the orbits of the four smaller moons and produced some surprising results. Mark R. Showalter of the SETI Institute in Mountain View, Calif., and Douglas P. Hamilton of the University of Maryland published their article in Nature this Wednesday.

Especially intriguing is the effect of the competing gravitational pulls of Pluto and Charon on the moon Nix, which seems to have a chaotic orbit. “It’s not just a little bit chaotic,” Dr. Showalter said. “Nix can flip its entire pole. It could actually be possible to spend a day on Nix in which the sun rises in the east and sets in the north. It is almost random-looking in the way it rotates.”

It is also possible that Styx and Kerberos have chaotic orbits, but measurements are not good enough to say for sure. Hydra also boasts a chaotic orbit.

NASA spacecraft to provide further information

The conclusions are based on Hubble images take between 2005 and 2012. Astronomers are excited to see what NASA’s New Horizons spacecraft can tell them about Pluto and its moons when it reaches it on July 14.

Although the orbits of the moons are not exactly in resonance, Dr. Showalter believes that the fact that they are so close means that they were once in resonance.

However a different kind of resonance was discovered between Styx, Nix and Hydra. Two kinds of resonance cannot occur at the same time, and the researchers believe that the original 5-moon resonance fell apart before the 3 moons synchronized their orbits.