MadSci Network: Astronomy

Re: How do Saturn's moons Janus and Epimethius change places?

Date: Mon Oct 2 01:24:33 2000
Posted By: Angelle Tanner, Grad student, Astronomy, UCLA
Area of science: Astronomy
ID: 969978639.As

Wow! I did not know about this at all. Thanks for bringing it
to my attention. It is kind of neat. 

A great web site to go to for information on the solar system is: 

The SEDS site says that the two moons have nearly equal orbital 
velocities and the lower, faster one slowly overtakes the other. 
"As they approach each other they exchange a bit of momentum
the end result of which is to boost the lower one into a higher orbit
and to drop the higher one to a lower orbit. They thus exchange places"

The quoted stuff is straight from the page. The important thing to remember 
about orbital mechanics is that you need more energy to get into a 
higher orbit. This is why the momentum exchange is important.

A good analogy is sometimes when my friend rollerblades behind me while I'm
biking, he likes to get a boost from me by grabbing my bike seat and 
transferring momentum from me to him. He goes shooting off ahead of me 
while I practically come to a halt. Give it a try. That is momentum 

Thanks for the cool question. 

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