1. The problem statement, all variables and given/known data A satellite is in a circular orbit very close to the surface of a spherical planet. The period of the orbit is 2.53 hours. What is the density of the planet? Assume that the planet has a uniform density. 2. Relevant equations T^2=(4pi^2r^3)/GM V=4/3piR^3 Density= Mass/ Volume 3. The attempt at a solution So far, I have calculated the amount of seconds in the orbit, but that is where my understanding of this comes to an abrupt halt. How could I get the radius without the speed of the satellite? Is it not true that the satellite could orbit ANY planet in 2.53 hours if it had enough speed? Some equations call for the gravity of planet, which is not given. I guess you could say that I need a little "Barney-style" walkthrough on this one.