What is the length of semi major axis of a planet in au with a period of 10.8 years?

To find the semi-major axis of a planet in astronomical units (AU) using Kepler's Third Law, we can use the formula ( a^3 = P^2 ), where ( a ) is the semi-major axis in AU and ( P ) is the orbital period in years. For a period of 10.8 years, we have:

[ a^3 = (10.8)^2 = 116.64 ]

Taking the cube root gives us:

[ a \approx 4.87 \text{ AU} ]

Thus, the semi-major axis of the planet is approximately 4.87 AU.