1. The problem statement, all variables and given/known data The planet Saturn will orbit the Sun every 19 Earth years (= 599 184 000 seconds). Assume Saturn travels on a circular orbit with a speed of 9 690m/s. What is the radius of the orbit of Saturn? I can solve this in two different ways, and get two different values. Which is the correct approach, & why? 2. Relevant equations & attempt at solution. T = (2πr)/V - that is, period is 2π*radius over speed., so, r = (T*V)/2π so, radius = 9.24 x 1011m However, if, the centripetal forces equals the universal law of gravitation, that is, Fc = Fg (m*v2)/r = (Gm1m2)/r2 r = (G*msun)/v2 r = [(6.67x10-11)(1.99x1030kg)]/(9690m/s2) r = 1.41 x 1012m So, why the difference? What applies, and what doesn't apply and why? Thanks!