Jupiter is the fifth planet from the Sun and by far the largest in the solar system, more than twice as massive as all the other planets combined (318 times Earth). It is a gas giant.
Jupiter is the fourth brightest object in the sky (after the Sun, the Moon and Venus; at some times Mars is also brighter). It has been known since prehistoric times. Galileo Galilei's discovery, in 1610, of Jupiter's four large moons Io, Europa, Ganymede and Callisto (now known as the Galilean moons) was the first discovery of a celestial motion not apparently centered on the Earth. It was a major point in favor of Copernicus's heliocentric theory of the motions of the planets; Galileo's outspoken support of the Copernican theory got him in trouble with the Inquisition.
Jupiter is composed of about 90% hydrogen and 10% helium (by numbers of atoms, 75/25% by mass) with traces of methane, water, ammonia and "rock". This is very close to the composition of the primordial Solar Nebula from which the entire solar system was formed. Saturn has a similar composition, but Uranus and Neptune have much less hydrogen and helium. Jupiter has a faint planetary ring system composed of dust particles.
A number of probes have visited Jupiter, all of them American in origin. [Pioneer 10]? flew past Jupiter in december of 1973, followed by [Pioneer 11]? exactly one year later. [Voyager 1]? flew by in 1977 and [Voyager 2]? in 1979. The [Galileo probe]? went into orbit around Jupiter in 1998(?), dropping a smaller subprobe into Jupiter's atmosphere and conducting multiple flybys of all of the Galilean moons. The Galileo probe also witnessed the impact of Comet Shoemaker-Levy 9 into Jupiter as it approached the planet, giving a unique vantage point for this spectacular event.
One of Jupiter's most distinctive features is the Great Red Spot, a large hurricane coloured by reddish methane-rich gasses welling up from lower in the Jovian atmosphere. The Great Red Spot is remarkably stable, having first been spotted by Galileo over 300 years ago.
Jupiter's moons fall into four major groups:
It is thought that the three groups of smaller moons may each have a common origin, perhaps as a larger moon or captured body that broke up into the existing moons of each group.
The Jovian moons in order of increasing orbital radius:
| Group | Name | Diameter (km) | Orbital radius (km) | Orbital period |
|---|---|---|---|---|
| 1 | Metis | 40 | 127,600 | 7.08 hours |
| Adrastea | 20 (23 x 20 x 15) | 134,000 | 7.11 hours | |
| Amalthea | 189 (270 x 166 x 150) | 181,300 | 11.92 hours | |
| Thebe | 100 (100 x 90) | 222,000 | 16.23 hours | |
| 2 | Io | 3632 | 421,600 | 1.76 days |
| Europa | 3126 | 670,900 | 3.55 days | |
| Ganymede | 5262 | 1,070,000 | 7.16 days | |
| Callisto | 4820 | 1,883,000 | 16.69 days | |
| 3 | Leda | 16 | 11,100,000 | 238.7 days |
| Himalia | 186 | 11,470,000 | 250.6 days | |
| Lysithea | 36 | 11,710,000 | 259.2 days | |
| Elara | 76 | 11,743,000 | 259.7 days | |
| 4 | Ananke | 30 | 20,700,000 | 617 days |
| Carme | 40 | 22,350,000 | 692 days | |
| Pasiphae | 50 | 23,300,000 | 735 days | |
| Sinope | 36 | 23,700,000 | 758 days |
All Jovian moons are tidally locked with Jupiter, and therefore have the same rotational period as their orbital period.
(Some information pasted from http://nineplanets.org/ using google for search. Additional information added since then.)
Solar system:
Sun - Mercury - Venus - Earth - Mars - Asteroids - Jupiter - Saturn - Uranus - Neptune - Pluto - Comets
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