1. Europa was one of the moons discovered by Galileo. It has a mass of 4.9E22 kg and a period of 3.6 days and distance of 6.7E8 m. What is the mass of Jupiter? 2. 3.6 days = 311040 sec F = G m m / r^2 F = Mv^2 / r T^2 = (4pi^2/Gm) R^3 3. I threw the numbers into Kepler's formula and get a negative exponent answer, and at this point im sort of lost. Somebody please put me in the right direction. And no I dont know exactly what the distance is from, but assume the obvious (whatever it may be) for the time being. Distance from the surface or from the center of Jupiter I dont know. I spent more time dwelling over this, and used 3 formulas: v = 2pi r/t to find the velocity of the moon's orbit. Then I used Kepler's formula T^2 = 3E-19 R^3 to find the radius of Jupiter (plugging 311040 sec into T). I think used the velocity and radius I calculated to find the mass of Jupiter using the formula v = sqrt(G m/r). I derived this formula by comparing centripetal force equation with Newtons law of universal gravitation (probably a memorized formula in most cases I would assume). Doing all of this, I got a value of 1.88E28. I double-checked with wikipedia and I am off by a decimal point (according to them). I assume I am now on the right track, but could someone just assure me that I used the right logic to come to my answer?