The orbital periods of Io, Europa, and Ganymede are in the ratio 1:2:4. Is there any significance to this?
A) No. This is just a random coincidence of the manner in which these satellites condensed out of the primordial nebula around Jupiter.
B) Yes. This is the ordering predicted by Kepler's third law.
C) Yes. Combined with the fact that these are all prograde orbits, this shows that these moons are not captured asteroids.
D) Yes. After completion of an orbit by Ganymede, all these moons will be in a line, creating tidal stresses on Io.

Question

Quizplus · Accepted Answer

The 1:2:4 ratio is a result of a Laplace resonance, which means that after Ganymede completes one orbit, Europa completes two, and Io completes four, aligning them periodically and causing tidal stresses on Io.

The Orbital Periods of Io, Europa, and Ganymede Are in the Ratio