Law of universal gravitation
In this equation
- F is the force of attraction
- G is the gravitational constant
- m1 and m2 are the masses of two bodies
- d is the distance between the two bodies
where the subscripts p and s represent the primary and the sun respectively, and m is the mass of the satellite.
The ratio of the two is
- Callisto–Jupiter distance (dp) is 1.883 · 106 km.
- Mass of Jupiter (Mp) is 1.9 · 1027 kg
- Jupiter–Sun distance (i.e. mean distance of Callisto from the Sun, ds) is 778.3 · 106 km.
- The solar mass (Ms) is 1.989 · 1030 kg
The table of planets
Asimov lists tug-of-war ratio for 32 satellites (then known in 1963) of the Solar System. The list below shows one example from each planet.
The special case of the Moon
Unlike other satellites of the solar system, the solar attraction on the Moon is more than that of its primary. According to Asimov, the Moon is a planet moving around the Sun in careful step with the Earth.