Jupiter
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). Some people have described our solar system as consisting of the Sun, Jupiter and various debris. It is a gas giant.
Voyager 1 took this photo of the planet Jupiter on January 24, while still more than 25 million miles (40 million kilometers) away. As the spacecraft draws closer to the planet (about 1 million kilometers a day) more details are emerging in the turbulent clouds. The Great Red Spot shows prominently below center, surrounded by what scientists call a remarkably complex region of the giant planet's atmosphere. An elongated yellow cloud within the Great Red Spot is swirling around the spot's interior boundary in a counterclockwise direction with a period of a little less than six days, confirming the whirlpool-like circulation that astronomers have suspected from ground-based photographs. Ganymede, Jupiter's largest satellite, can be seen to the lower left of the planet. Ganymede is a planet-sized body larger than Mercury. This color photo was assembled at Jet Propulsion Laboratory's Image Processing Lab from three black and white images taken through filters. click here for full-sized image
- Orbital radius: 778,330,000 km (5.20 AU) from Sun
- Aphelion: 815,700,000 km
- Perihelion: 740,900,000 km
- Diameter: 142,984 km (equatorial)
- Surface area: 6.41×1010 km2
- Mass: 1.899×1027 kg
- Rotational period: 9.84 hours
- Orbital period: 4333 days
- Axial tilt: 3.12°
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 has a very large and powerful magnetosphere. In fact, if you could see Jupiter's magnetic field from Earth, it would appear five times as large as the full moon in the sky despite being so much farther away. This magnetic field collects a large flux of particle radiation in Jupiter's radiation belts, as well as producing a dramatic gas torus and flux tube associated with Io.
The orbits of Io, Europa and Ganymede form a pattern known as the Laplace resonance; for every four orbits that Io makes around Jupiter, Europa makes exactly two orbits and Ganymede makes exactly one. This resonance causes the gravitational effects of the three moons to distort their orbits into elliptical shapes, since each moon recieves an extra tug from its neighbours at the same point in every orbit it makes. The tidal force from Jupiter, on the other hand, works to circularize their orbits. This constant tug of war causes regular flexing of the three moons' shapes, Jupiter's gravity stretching the moons more strongly during the portion of their orbits that are closest to it and allowing them to spring back to more spherical shapes when they're farther away. This flexing causes tidal heating of the three moons' cores. This is seen most dramatically in Io's extraordinary volcanic activity, and to a somewhat less dramatic extent in the geologically young surface of Europa indicating recent resurfacing.
Jupiter's moons fall into four major groups:
- The inner group were all discovered during the Voyager project (except for Amalthea), all have diameters of less than 200 km and orbit at radii less than 200,000 km, and have orbital inclinations of less than half a degree.
- The Galilean moons were all discovered by Galileo Galilei, orbit between 400,000 and 2,000,000 km, and include the largest moons in the solar system.
- The third group were all discovered in the 20th century but before Voyager, have diameters less than 200 km, and orbit between 11,000,000 and 12,000,000 km with an orbital inclination between 26° and 29°.
- The outer moons were also discovered in the 20th century before Voyager, but have diameters under 50 km and orbit between 21,000,000 and 24,000,000 km. They are particularly notable for having retrograde orbits with inclinations between 147° and 163°.
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 (40 x 60) | 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.
This dramatic view of Jupiter's Great Red Spot and its surroundings was obtained by Voyager 1 on February 25, 1979, when the spacecraft was 5.7 million miles (9.2 million kilometers) from Jupiter. Cloud details as small as 100 miles (160 kilometers) across can be seen here. The colorful, wavy cloud pattern to the left of the Red Spot is a region of extraordinarily complex and variable wave motion. To give a sense of Jupiter's scale, the white oval storm directly below the Great Red Spot is approximately the same diameter as Earth. click here for full sized image
(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