Timeline of discovery of Solar System planets and their moons

The timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. Each object is listed in chronological order of its discovery (multiple dates occur when the moments of imaging, observation, and publication differ), identified through its various designations (including temporary and permanent schemes), and the discoverer(s) listed.

Historically the naming of moons did not always match the times of their discovery. Traditionally, the discoverer enjoys the privilege of naming the new object; however, some neglected to do so (E. E. Barnard stated he would "defer any suggestions as to a name" [for Amalthea] "until a later paper"[1] but never got around to picking one from the numerous suggestions he received) or actively declined (S. B. Nicholson stated "Many have asked what the new satellites" [Lysithea and Carme] "are to be named. They will be known only by the numbers X and XI, written in Roman numerals, and usually prefixed by the letter J to identify them with Jupiter."[2]). The issue arose nearly as soon as planetary satellites were discovered: Galileo referred to the four main satellites of Jupiter using numbers while the names suggested by his rival Simon Marius gradually gained universal acceptance. The International Astronomical Union (IAU) eventually started officially approving names in the late 1970s.


In the following tables, planetary satellites are indicated in bold type (e.g. Moon) while planets and dwarf planets, which directly circle the Sun, are in italic type (e.g. Earth). The Sun itself is indicated in roman type. The tables are sorted by publication/announcement date. Dates are annotated with the following symbols:

  • i: for date of first imaging (photography, etc.);
  • o: for date of first human visual observation, either through telescope or on photographic plate;
  • p: for date of announcement or publication.

In a few cases, the date is uncertain and is then marked "(?)".

* Note: Moons marked by an asterisk (*) had complicated discoveries. Some took years to be confirmed, and in several cases were actually lost and rediscovered. Others were found in Voyager photographs years after they were taken.

Color legend

The planets and their natural satellites are marked in the following colors:

  • Other designations are synonyms or periphrases sometimes encountered for the object.
  • Permanent designations (of planetary satellites) are explained here.
  • Temporary designations are explained here.
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