User:Iridia/J 2

The quadrupole gravitational coefficient ${\displaystyle J_{2}}$ is a dimensionless value used in planetary physics to measure the distortion of the gravitational field of a spinning, oblate spheroid planet. A stationary planet will be perfectly spherical, and have a spherical surrounding gravitational potential: as its rotation speed increases, the planet will deform under the centrifugal force, developing an equatorial bulge. This redistribution of mass alters the shape of the gravitational potential around the planet. The magnitude of ${\displaystyle J_{2}}$ provides information on the planet's internal density structure, including the size of its most dense region, the core. ${\displaystyle J_{2}}$ is best found by measuring the path of spacecraft in orbit around or flying by a planet. It can also be calculated, though with less precision, if the spin of a planet can be measured.