Planetary names in our Solar System are derived from mythology – except for Earth, which comes from Middle English. Since five of the planets can be seen by the naked eye, they have been called many things depending on the culture over the centuries before their current names became standard.
Uranus (previously thought to have been a star) is the only planet whose name comes from Greek rather than Roman mythology. Neptune’s discoverers argued over who could name it, while former planet Pluto’s name was suggested by an 11 year old in the UK. There were no planetary naming rules until 1919, when the International Astronomical Union (IAU) formed. The IAU is currently in charge of naming all celestial objects.