Quote:
Originally Posted by akasha View Post
I'm no expert, but one of my relatives is an astrophysicist and I actually asked him the same question about a year ago. Apparently, such subsatellites would be very rare as it wouldn't be possible for a subsatellite to be in stable orbit around most moons. There might be exceptions but, at the time, there were no known exceptions. I'm not sure if we've found any since then.

As for what it would be called, it would seem we use "moon of a moon," as "moon" just means "natural satellite."
There are still no known exceptions (though I work on stellar atmospheres not satellites so I may have missed a paper or two).