The Earth, Moon, Mars and the giant planets

Jupiter is the largest planet: equatorial radius ≈ 71,500 km, mass ≈ 318 times the Earth’s, rotation 9 h 50 min; the Great Red Spot is a giant storm that has lasted for centuries. It has more than 90 known moons; four of them – Io, Europa, Ganymede and Callisto – were discovered by Galileo in 1610. Ganymede is the largest moon in the Solar System (bigger than Mercury), Io is the most volcanic body, and Europa may have an ocean beneath its ice crust. Saturn: radius ≈ 60,300 km, mass 95 Earth masses, mean density less than water (≈ 0.69 g/cm³); its rings are mostly water-ice particles, hundreds of thousands of km wide yet very thin. It has more than 200 known moons; Titan has a dense nitrogen atmosphere (the Cassini–Huygens mission landed a probe in 2005) and Enceladus has geysers. Uranus (1781, Herschel) rotates tilted by 98°, and Neptune was found in 1846 by calculation (Le Verrier, Adams; observed by Galle); both are ice giants with faint rings. Only Voyager 2 has visited them (1986 and 1989). The Juno probe entered orbit around Jupiter in 2016.