According to Kepler's third law the square of the planets period in years is?

T^2 is proportional to r^3 (or a^3).

More exactly, T^2 = (2*pi)^2/(GM)*r^3 (or a^3).

Where...

• T is the period
• r is the radius of the orbit
• a is the length of the semimajor axis of the orbit
• pi is about 3.142
• G is the gravitational constant 6.67x10^-11
• M is the mass of the planet