7 Things We've Learnt About Pluto Since New Horizons

5. Its Other Moons Are Just Plain Weird

Aside from Charon, Pluto has four much smaller, much weirder moons: Styx, Nix, Kerberos and Hydra. These moons are a chaotic mess of shapes and sizes, spinning at all sorts of speeds and directions. Hydra, for example, spins 89 times for every orbit it makes around Pluto. These pill-shaped moons are odd, as it is more often the case that a planet's moons will have settled down into a synchronous orbit, with its orbit and spin taking the same length of time - this means that just one side will always face its host planet. Earth's moon is like this, which is why its surface always looks the same from our vantage point. Scientists reckon that it is the influence of the mighty Charon that is preventing Pluto's other moons from settling down. Its greater gravitational field exerts a strong torque on the other bodies and keeps them spinning like tops. It's also thought that their movements could be due to collisions with other smaller moons at some point in Pluto's history. It's likely that Pluto once had many more moons that kept crashing into one another. Indeed, scientists thought that we would discover lots of smaller moons left over from these collisions during the New Horizons flyby, but it turns out that the ones we discovered from Earth are all little Pluto has to offer.