User:Physchim62/Planetmass

Planetary mass is a measure of the mass of a planet. Within the Solar System it is usually measured in the astronomical system of units, where the unit of mass is the solar mass, that is the mass of the Sun.

The mass of a planet within the Solar System is an adjusted parameter in the preparation of ephemerides. There are two basic procedures for measurement:

• If the planet has natural satellites, its mass can be calculated from Kepler's third law. The same procedure can be used for data from space probes such as the Voyager probes to the outer planets and the MESSENGER spacecraft to Mercury.
• The mass of a planet can also be inferred from its effect on the orbits of other planets.

In practice, both methods are used. The ephemeris is a model of the Solar System, and the planetary masses within that model are adjusted so as to give the best fit between the model and the observed positions of the planets.