The equation t^2=a^3 shows the relationship between a planet’s orbital period, t, and the planet’s mean distance from the sun, a, in astronomical units, au. if planet y is twice the mean distance from the sun as planet x, by what factor is the orbital period increased? a. 2^1/3. b. 2^1/2. c. 2^2/3. d. 2^3/2