ESO Astronomical Glossary - J
Jupiter
Jupiter is the largest planet in our solar system. It has a thick, gaseous atmosphere, more than 60 satellites (moons) and a dark ring. Jupiter's most prominent features are distinctly coloured bands across its latitudes and the Great Red Spot, which is a storm in the planet's upper atmosphere with the same size as the planet Earth. The adjective commonly used for Jupiter-like bodies is 'Jovian'.
Jovian Planet
Jovian planet is a term used for the four largest planets in the solar system: Jupiter, Saturn, Uranus, and Neptune. However, in recent decades astronomers have found notable differences between the planets: while Jupiter and Saturn are gaseous planets, Uranus and Neptune consist mainly of rock and ice - hence the term 'Jovian planets' has become obsolete in this context. More recently, however, it has been used to describe Jupiter-like gas giants discovered round other nearby stars (see exoplanet.)