Hey all, I spelt "Epimetheus" wrong in this tweet of some amazing image processing, so to make up for it, I'm gonna tweet a thread of little factoids about the moon.
1) it looks like a potato that's been swiss cheesed.
(This image was taken by Cassini (❤) in 2007. Credit: NASA/JPL/Space Science Institute)
(This image was taken by Cassini (❤) in 2007. Credit: NASA/JPL/Space Science Institute)
2) it's small, only about 72 miles (or 116 km) across!
3) at about 94,000 miles (151,000 km) from Saturn, it takes just 17 hours to make one full orbit about the planet. Plugging these into a calculator tells me it has an orbital speed of ~55,000 km/h! (But wait---the distance thing gets really interesting because gravity is awesome)
4) Epimetheus has a dance partner. They swing each other throughout this dance so that they swap spots in their orbital game: Janus. Janus is a total potato.
(Image taken by Cassini (❤) in 2010. Credit: NASA / Jet Propulsion Laboratory / Space Science Institute)
(Image taken by Cassini (❤) in 2010. Credit: NASA / Jet Propulsion Laboratory / Space Science Institute)
(Yes I'll always put a ❤ in any time I mention Cassini. ❤ =') )
5) the two moons only differ by about 31 miles (50 km) in distance from Saturn, so that their gravitational interaction is strong enough to keep them in this "co-orbital resonance".
6) When one (let's say it's Epimetheus) is closer in, it orbits just a bit faster than the other (Janus) does. And here's where the distance thing gets interesting: this difference in orbital speed is such that it takes about 4 years for Janus to catch up to Epimetheus.
7) when the two get close, their gravitational attraction increases enough for them to sort of swap orbital angular momentum, which is when they swing each other and swap spots!
(It's a bit more involved than that since Janus is more massive. And Saturn has particles in its orbit, so Epimetheus and Janus tug on house too. Check out @elakdawalla's post on this gravitational dance, here: planetary.org/blogs/emily-la…)
8) so, not only is Epimetheus a cute swiss cheesed potato moon, but it has a friend to dance with throughout its journey around the ringed planet! =)
