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JPL Solar System Dynamics
Planetary Satellites

Planetary satellites (often called "moons") are not to be confused with man-made satellites (such as weather and communications satellites) in orbit around the Earth. Planetary satellites are small bodies in orbit about a planet (actually the planet's system barycenter). Probably the best known planetary satellite is Earth's moon. Currently, we know of no satellites in orbit around Mercury or Venus. All the other planets have at least one known planetary satellite.

Mean Orbital Elements

Tables showing mean orbital elements are available. These should not be used for computing precise positions (please use HORIZONS instead), but instead might be used to gain a rough sense of a satellite's orbital shape.

Physical Parameters

Selected physical parameters such as GM, mean radius, mean density, magnitude, and geometric albedo are available for some planetary satellites. These parameters are presented in a table with references. In addition, there is a JPL lunar constants and models technical document available in PDF format.


Planetary satellite ephemerides are available using JPL's HORIZONS system. Although mean orbital elements are also available for planetary satellites, you are strongly discouraged from using them to generate your own ephemerides, as they will be highly inaccurate for many bodies. The list of planetary satellite ephemerides available via HORIZONS is available in this table.

SPK ephemeris files are available from JPL's NAIF site under the "data" section. These data will be useful to users of the NAIF SPICE toolkit.

Optical and Radar Astrometry

Optical and radar astrometry as well as spacecraft measurements used in the planetary satellite ephemerides are available on this site.

Discovery Circumstances

Planetary satellite discovery circumstances are available in a separate table. This table includes the satellite provisional designation, IAU number (if assigned), IAU name (if assigned), year of discovery, a list of discoverers, and references (where known).

Gravity Fields for the Outer Planets

Gravity field data used in our planetary satellite orbit determination models for the outer planets (Jupiter, Saturn, Uranus, and Neptune) is given in a table with references.

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