1. The problem statement, all variables and given/known data Consider the earth's orbit around the sun orbit as circular. Suppose the sun slowly loses mass from mass M1 to mass M2. Suppose that the initial orbit is R1 and the final orbit is R2. Express R2 in terms of the other parameters. 2. The attempt at a solution The problem I'm having here is relating the two equations for the gravitational force initially and finally. I can't think what is conserved in this situation. The final answer is supposed to be M1R1/M2. Looks like something to do with moments but I can't figure out what.