This is Kepler's third law: Because the mass of the comet (or planet) has canceled
out, the law says that for all bodies orbiting the sun, the square of the period is
proportional to the cube of the semimajor axis. (For circular orbits, we can replace
a 3by r3 .) The law applies equally to the satellites of any large body. For example, all
satellites of the earth, including the moon, obey the same law [with Ms replaced by
the earth's mass Mein (8.55)], and the same applies to all the moons of Jupiter.