Jupiter

Jupiter: Note the Great Red Spot to the lower right and the shadow of Europa on the lower left

Image is from the Cassini Spacecraft

 

Jupiter is by far the largest planet in the solar system in terms of mass and size. However, it is still less then 99% of the Sun's mass. It has a semi-major axis distance of 5.2 AU which gives it an orbital period of about 11 years. It rotates once on its axis every 10 hours, making it one of the fastest rotating bodies in the Solar System.

Previously, we had talked about Galileo and how he had discovered the first moons around a planet other than our Earth. This discovery helped prove the geocentric theory of the solar system was incorrect (Objects can orbit something other than the Earth). Galileo originally wanted to call them the Medician moons after his sponsors, the Medicis, but it was eventually agreed to name them the Galilean moons and to name them after four of the lovers of Zeus; Io, Europa, Ganymede, and Callisto.

Saturn is no the only planet with rings. In fact, all four Jovian planets have a ring system, though not quite as magnificent as Saturn's rings. Jupiter's rings are not as extensive as the rings around Saturn and were not discovered until 1979 by Voyager 1.

Jupiter is also home to the largest storm in the Solar System. The Great Red Spot is at least 183 years old and may be older. It may have been first observed in 1665, but it isn't clear if it was observed again until 1831. It is between 24,000 to 40,000 km east-west and 12,000 to 14,000 km north-south, making it capable of holding 2 to 3 Earths.

Jupiter also shares its orbit with a two groups of asteroids known as the Greek and Trojan asteroids. These asteroids were discussed previously here. These asteroids, much like the Amor asteroids, will never impact Jupiter. However, Jupiter's gravity is strong enough to capture both asteroids and comets. Many of Jupiter's moons are possibly captured asteroids, and back in 1994, Comet Shoemaker-Levy 9 entered Jupiter's gravitational field, broke up, and collided with Jupiter.

Jupiter has a very thick atmosphere, as the majority of its volume are the many layers of gas. There is a rocky core, approximately Earth-sized, but is only a small fraction of the entire diameter of Jupiter. The combination of its large volume and the majority of the composition of the planet give Jupiter the largest mass of all the planets, but also a low density, just a little bit above that of water.