A Guide to Planetary Satellites
Use these up-to-date tables to explore the wide-ranging assortment of moons, big and small, that populate our solar system.
However, the advent of sensitive electronic cameras has put telescopic observers back in the driver's seat, resulting in dozens of finds over the past few years. Indeed, some of the new objects are so small, only a few kilometers across, that they stretch the traditional notion of what constitutes a "moon." Sometimes faint objects appear fleetingly in images and are never seen again; others require patient follow-up observations over months or years to confirm their reality. While comets bear the surname(s) of their discoverer(s), and observers retain naming rights for asteroids, those who spot planetary moons must yield this privilege to the International Astronomical Union. By convention, the IAU does not name a satellite until its orbit is known precisely a threshold sometimes not reached until decades after the initial discovery.
The following is a tabulation of known planetary satellites, last updated in July 2012. As of then, the count stood at 173, distributed as follows: Earth 1, Mars 2, Jupiter 67, Saturn 62, Uranus 27, Neptune 13. Among the dwarf planets, Pluto has 5, Eris 1, and Haumea 2. However, the locations of 11 Jovian and seven Saturnian moonlets are known so poorly that they are effectively lost.
In the table below and on the following pages, the Diameter of each satellite and the Orbital distance from its planet's center (semimajor axis) are in kilometers; Eccentricity (Ecc.) is the elongation of the satellite's orbit; and Inclination is the tilt of its orbit plane, in degrees, with respect to the planet's equatorial plane (for inner moons) or the ecliptic plane (for outer moons). Names of "lost" objects are shown in italics.
|Confirmed List of Planetary Satellites|