Posted by **mymi** on Sunday, October 30, 2011 at 8:58pm.

An asteroid is discovered to have a tiny moon that orbits it in a circular path at a distance of 122 km and with a period of 43 h. The asteroid is roughly spherical (unusual for such a small body) with a radius of 19 km.

(a) Find the acceleration of gravity at the surface of the asteroid.

and

(b) Find the escape velocity from the asteroid.

I can find the escape velocity once I calculate part a and for part a I know the formula, but how do I find M to plug in?