1. The problem statement, all variables and given/known data An approach to the problem of finding how orbital radius changes with solar mass is to solve the radial equation of motion for a gravitational force that has an explicit time dependence based on the assumed rate of mass loss. Show by numerically solving this equation of motion that one gets the result D proportional to 1/M. 2. Relevant equations I'm not entirely sure what equation of motion the question requires. We can equate the gravitational force with the centripetal force, mv2/D = GMm/D2 but I'm unsure as to how to include the time-dependent solar mass. I think we can assume the changes in mass per orbit are small and uniform. 3. The attempt at a solution I tried replacing the constant mass M in the above equation with M(t) and differentiating with respect to t, and using the angular momentum to express v in terms of D, but it's not really getting me anywhere. Any advice on how to approach this problem would be greatly appreciated. :D Thanks!