Simulation of the moon Nix which orbits Pluto every 25 days. Here that’s sped up to one orbit every two seconds, so we can see its chaotic spin more clearly.
Little moons in the solar system have it tough. Some were once free-roaming asteroids until they were captured by the gravity of a planet. Others, because of their small size and irregular shape, get pushed around in unpredictable ways by their parent planet.
Tumbling end-over-end like a dropped baton in a relay race, it’s fascinating to watch Pluto’s moon Nix wobble about in a state of orbital chaos. That’s what scientists call it. Chaos. It means no matter how many times you solve the equation, you will never predict with certainty how a body will spin. Analysis of data from NASA’s Hubble Space Telescope shows that two of Pluto’s moons, Nix and Hydra, wobble unpredictably.
If you lived on either, you’d never know when and in what direction the Sun would rise. I don’t know if that would be fun or frustrating. Definitely a challenge for the old biological clock. Imagine if the Sun rose in the east on your way to work one day and then rose in the west on the next. Or if it stayed up 5 hours today and 12 tomorrow. I have to agree. Chaos.
Nix and its fellow small moons Kerberos, Styx and Hydra wobble because they’re embedded in the strong-arm gravity field of the Pluto-Charon duo. I say duo because Pluto and Charon are similar enough in size to be considered a “double planet”. Charon’s 750 mile (1,212 km) girth is half as big as Pluto’s.
As the duo dances an orbital duet about their common center of gravity, their variable gravitational field causes the smaller moons to tumble erratically. The effect is enhanced by their irregular and elongated shapes. These diminutive satellites have company. Saturn’s moon, Hyperion, which we visited in a recent blog, also tumbles chaotically.
The discovery was made by Mark Showalter of the SETI Institute and Doug Hamilton of the University of Maryland using the Hubble Space Telescope and published in today’s issue of the journal Nature.
That’s not all. The two gents also determined that Kerberos is as dark as the charcoal briquettes you use to grill your burgers and brats, while the other moons reflect brightly like beach sand. That’s because they’re mostly made of ice. So what makes Kerberos different? Astronomers and you and me want to know.
So how did all these little moons get to orbit an object that’s so small it’s not even considered a planet? It’s thought that a collision between the dwarf planet and a body of similar size happened over 4 billion years during the solar system’s infancy. The moons are leftover shards from the crack-up that eventually took up orbits around the present-day Pluto. Outside of Charon, the biggest piece, the other four moons are only a few tens of miles across. What do you bet there are more there for the finding. Small and reflecting the light of the remote Sun, they remain hidden for now. Perhaps New Horizons will find them when it whizzes by the Pluto system on July 14.