The period of a planetary orbit about a star is one Earth year, whereas the average distance between the planet and the star is 1.5 AU (astronomical units). A second planet is orbiting the star at a distance of 6.0 AU. The period of the second planet orbiting the same star is

Question

Quizplus · Accepted Answer

According to Kepler's Third Law, the square of the orbital period (T) is proportional to the cube of the semi-major axis (a) of its orbit. For the first planet, T^2 = a^3, so (1 year)^2 = (1.5 AU)^3. For the second planet, T^2 = (6.0 AU)^3. Solving gives T ≈ 8 years.

The Period of a Planetary Orbit About a Star Is