[GeronL]

OK.. I can understand capturing them but how do they escape again? It’s not like their speed increases, right?

[Tea Party Terrorist]

Global Warming.

[KC Burke]

Let’s imagine the first eleven passes aren’t near the gravitational influence of the moon but number twelve is — bingo.

[munin]

OK.. I can understand capturing them but how do they escape again? It’s not like their speed increases, right?

Slingshot effect, that is how the Explorers and Viking sat. was sent out of the solar system

[cripplecreek]

Here’s a cool little orbital/gravity simulator that might help visualize who it might happen.

http://www.nowykurier.com/toys/gravity/gravity.html

[jmcenanly]

Their orbits may be perturbed by other bodies in the solar system, or else they may simply collide with other objects.
Here is a page that explains the LaGrange, or libration points in a little more detail than this article provides. It may make things a little clearer.