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Ephemerides

High precision ephemerides for solar-system bodies are available on-line using JPL's HORIZONS system. Most optical and radar observers will be best served by using our HORIZONS system to generate custom observer-table ephemerides. Our on-line HORIZONS system can also be used to output ephemerides in the form of osculating orbital elements and/or Cartesian vectors (position, velocity, and acceleration). However, there are some ephemeris data files available for export (see below) for those rare cases when HORIZONS will not suffice.

Professionals requiring high-precision ephemerides readable from their own software may find ephemeris data files (in SPK format) and a software toolkit needed to read those files from JPL's NAIF web-site. SPK files for planetary and planetary satellite ephemerides are available from NAIF. Comet and asteroid SPK files may be generated using our HORIZONS system.

Planets

Planetary ephemerides are available using JPL's HORIZONS system. Although the HORIZONS system will be sufficient for the vast majority of ephemeris requests, JPL planetary and lunar ephemeris files (e.g. DE406) are also available. The use of these ephemeris files is recommended only for professionals whose needs are not readily met by the HORIZONS system. Alternatively, you may use the NAIF SPICE toolkit and planetary ephemerides in SPK format from JPL's NAIF web-site.

As a low-precision alternative suitable for many applications, approximate positions of the planets can be computed from their orbital elements as described in a separate page.

Summary of available planetary ephemerides:

Planetary Satellites

Ephemerides for planetary satellites are available from 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.

Comets & Asteroids

Ephemerides for comets and asteroids are available from JPL's HORIZONS system. SPK ephemeris files can also be custom generated using HORIZONS for use with JPL's NAIF SPICE toolkit.

Spacecraft

The Solar System Dynamics Group does not create spacecraft ephemerides. However, JPL's HORIZONS system can access trajectory solutions provided by the navigation teams of many missions and derive many ephemeris quantities related to position and velocity.

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