In June, research by Mark Showalter (SETI) and Doug Hamilton (Maryland University), in the USA, showed that the rotation of the moons Nix, Hydra, Kerberos and Styx, was not constant and varied unforeseeably over time.


The physicists from Aveiro have now found an explanation for the phenomenon and published their work in the latest edition of "Astronomy & Astrophysics Letters".


Alexandre Correia, research coordinator and solar system specialist said two factors distinguished these four small moons from the others, namely Charon, Pluto’s other moon, which has a regular rotation.


“As the four moons are very small, less that 50 km across, they are more potato-shaped that spherical, so they always have one axis longer than the others”, he explained.


Another factor that makes Nix, Hydra, Kerberos and Styx unique is that unlike other these four small moons, Pluto’s largest moon, Charon, is almost as big as the dwarf planet itself, so technically the Pluto-Charon system should be classified as a binary system rather than a planet-moon system”.