Astronomy help?

nothankyou1110 · #1 (**permalink**) 04-29-2008, 09:57 PM

Suppose a planet with a mass of 2.36E-3 solar masses is orbiting a 1 solar mass star.
If the planet orbits the star in 1.64 years, how many astronomical units away from the star must the planet be?

Okay... so I know that I should possibly use the kepler law.. but I am not a 100% sure how to work out this problem!

eri · #2 (**permalink**) 04-29-2008, 09:58 PM

p^2 = a^3, where p is the period in years and a is the radius in astronomical units. So you need to solve this for a.

a = (p^2)^(1/3) = p ^ 2/3. Doesn't depend on the mass.

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