Planetary Mass (1 Viewer)

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Planet X is observed to have a small moon. This moon is observed to orbit the planet once per month at a distance of 15 Planet X diameters. What is the mass of Planet X in solar masses? [Hint: Use Newton's form of Kepler's Third Law: P2 is proportional to a3/M, where M is the mass of Planet X (assuming that the mass of the moon is negligible in comparison).]

the diameter of planet X is .0008 au as derived from previous problems. so 15 planet x diameters would be .012

So this would be a correct?
And p would be 30 days?

so the mass would be M = .012^3/30^2?

If this is correct am i missing something because i cannot come up with the correct anwer.
Last edited:
figured it out.... thanks anyway

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