Dermott's law

Dermott's law is an empirical relation in which the orbital periods of successive regular satellites approximately form a geometric progression, with nearly constant ratios between adjacent periods.

Connect

Orbital period: The time an orbiting body takes to complete one revolution around its primary. Dermott's law compares the orbital periods of neighboring satellites.
Jupiter's moons: The natural satellites orbiting the planet Jupiter. The period spacing of Jupiter's regular moons motivated tests of Dermott's relation.
Stanley Dermott: A British-American astronomer known for research on celestial mechanics and planetary satellite systems. Dermott's studies of satellite orbital spacing gave the empirical relation its name.
Laplace resonance: A three-body resonance among Io, Europa, and Ganymede, whose orbital periods are close to a 1:2:4 ratio. It is a specific dynamical resonance, unlike the broader approximate progression described by Dermott's law.
Geometric progression: A sequence in which each term is obtained by multiplying the previous term by a constant ratio. The law describes satellite periods as an approximate geometric progression.
Saturn's moons: The natural satellites orbiting the planet Saturn. Saturn's regular satellites offer a second system for comparing adjacent orbital periods.
Titius–Bode law: An empirical rule that approximates the distances of planets from the Sun with a numerical sequence. It is a better-known proposed orbital-spacing regularity, but concerns planetary distances rather than satellite periods.
Orbital resonance: A gravitational configuration in which orbiting bodies' periods or frequencies have a ratio of small integers. Resonance is a distinct dynamical condition that can coexist with, but is not equivalent to, regular period spacing.
Mean-motion resonance: A dynamical relationship in which orbiting bodies' orbital frequencies are close to a ratio of small integers. Period ratios in satellite systems can lie near resonant ratios without exact resonance being required.
Uranus's moons: The natural satellites orbiting the planet Uranus. Their orbital periods provide another test of whether regular-satellite spacing follows the relation.