Laplace Plane - The Work of Laplace

The Work of Laplace

The Laplace or Laplacean plane, as discussed here, relates to the orbit of a planetary satellite. It is to be distinguished from another and quite different plane, also discovered by Laplace, and which is also sometimes called the "Laplacian" or "Laplace plane", but more often the invariable plane (or the "invariable plane of Laplace"). The invariable plane is simply derived from the sum of angular momenta, and is "invariable" over the entire system, while the Laplace plane may be different for different orbiting objects within a system. Confusingly, a satellite's Laplace plane (as defined here) is also sometimes called its "invariable plane".

The Laplace plane is a result of perturbational effects, which were discovered by Laplace while he was investigating the orbits of Jupiter’s principal moons (the Galilean satellites of Jupiter). Laplace found that the effects of the solar perturbing force, and of the planet’s oblateness (its equatorial bulge), together gave rise to an "inclinaison propre", an "own inclination", in the plane of the satellite orbits, relative to the plane of Jupiter’s equator.