The stronger the gravitational force, the shorter the orbital period.
In other words, the greater the gravitational attraction of its sun, the faster the planet must go to stay in the same orbit.
The formula for the orbital period <em>P</em> is
<em>P</em> = 2π√[<em>r</em>^3/(<em>GM</em>)]
where
<em>r</em> = the average radius of the orbit
<em>G</em> = the gravitational constant
<em>M</em> = the mass of the planet’s sun
The important point is that the orbital period is <em>inversely proportional</em> to the square root of the sun’s mass.
The gravitational attraction of the sun is <em>directly proportional</em> to its mass.
Thus, as mass increases, gravitational attraction increases, and the orbital period decreases
