Former member of the Solar System Pluto has taken a lot of grief over the years, what with being downgraded to a dwarf planet and all. Now, as though things couldn’t get more embarrassing for the tiny, rocky sphere a new study by the University of Maryland and the SETI Institute using the Hubble Space telescope reveal the sharpest detail about Pluto and its moons to date. Of the findings, the most interesting is this: Two of Pluto’s moons, Nix and Hydra, have orbits that wobble like a couple of drunks.
“Like good children, our moon and most others keep one face focused attentively on their parent planet,” said Douglas Hamilton, professor of astronomy at the University of Maryland and a co-author of the Nature study. “What we’ve learned is that Pluto’s moons are more like ornery teenagers who refuse to follow the rules.”
Indeed, were you to be standing on either moon, the wobbles in their axes would make it difficult to know when and from where the Sun would rise each day. The unpredictability is the result of Pluto and it’s largest moon Charon, which essentially operate as a “binary planet” (poor Pluto – it can’t seem to have its own moment). The two share a center of gravity, and because they orbit around one another (rather than Charon orbiting Pluto, as a moon ought to) their constant tug of war creates a fluctuating gravitational field for the smaller, orbiting moons.
“Hubble has provided a new view of Pluto and its moons revealing a cosmic dance with a chaotic rhythm,” said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate in Washington. “When the New Horizons spacecraft flies through the Pluto system in July we’ll get a chance to see what these moons look like up close and personal.”
Not helping things is the fact that the moons are more oblong than round, because nothing can be normal with Pluto. Oddly enough, Styx, Nix and Hydra orbit in a locked resonance, meaning they don’t crash into each other. It’s this, the scientists say, that allows Pluto to have so many moons despite its size.