Jupiter

Click image for description
Orbital characteristics (Epoch J2000)
Semi-major axis	778,412,027 km 5.203 363 01 AU
Orbital circumference	4.888 Tm 32.675 AU
Eccentricity	0.048 392 66
Perihelion	740,742,598 km 4.951 558 43 AU
Aphelion	816,081,455 km 5.455 167 59 AU
Orbital period	4335.3545 d (11.87 a)
Synodic period	398.86 d
Avg. Orbital Speed	13.050 km/s
Max. Orbital Speed	13.705 km/s
Min. Orbital Speed	12.440 km/s
Inclination	1.305 30° (6.09° to Sun's equator)
Longitude of the ascending node	100.556 15°
Argument of the perihelion	274.197 70°
Number of satellites	63
Physical characteristics
Equatorial diameter	142,984 km [1] http://www.onasch.de/astro/showobject.php?lang=en&obj=p05 (11.209 Earths)
Polar diameter	133,709 km (10.517 Earths)
Oblateness	0.064 87
Surface area	6.14×1010 km2 (120.5 Earths)
Volume	1.338×1015 km3 (1235.6 Earths)
Mass	1.899×1027 kg (317.8 Earths)
Mean density	1.326 g/cm3
Equatorial gravity	23.12 m/s2 (2.358 gee)
Escape velocity	59.54 km/s
Rotation period	0.413 538 021 d (9 h 55 min 29.685 s) 1 http://www.hnsky.org/iau-iag.htm
Rotation velocity	12.6 km/s = 45,300 km/h (at the equator)
Axial tilt	3.13°
Right ascension of North pole	268.05° (17 h 52 min 12 s)
Declination	64.49°
Albedo	0.52
Surface temp.	min mean max 110 K 152 K N/A K
Atmospheric characteristics
Atmospheric pressure	70 kPa
Hydrogen	~86%
Helium	~14%
Methane	0.1%
Water vapor	0.1%
Ammonia	0.02%
Ethane	0.0002%
Phosphine	0.0001%
Hydrogen sulfide	<0.0001%

Jupiter is the fifth planet from the Sun and by far the largest within our solar system; some have described the solar system as consisting of the Sun, Jupiter, and assorted debris. It and the other gas giants Saturn, Uranus, and Neptune are sometimes referred to as "Jovian planets." It was named after the Roman god Jupiter (also called Jove). Its symbol is a stylized representation of the god's lightning bolt (Unicode: ♃).

Contents

1 Overview 2 Physical characteristics 2.1 Planetary composition 2.2 Atmosphere 2.3 Planetary rings 2.4 Magnetosphere 3 Exploration of Jupiter 3.1 Pioneer flyby missions 3.2 Voyager flyby missions 3.3 Galileo orbiter 3.4 Cassini flyby mission 3.5 Future probes 4 Jupiter's moons 4.1 Galilean moons 4.2 Classification of Jupiter's moons 5 Cometary impact 6 Jupiter in fiction and film 7 External links

Overview

Jupiter is 2.5 times more massive than all the other planets combined, so massive that its barycenter with the Sun actually lies above the Sun's surface (1.068 solar radii from the Sun's center). It is 318 times more massive than Earth, with a diameter 11 times that of Earth, and with a volume 1300 times that of Earth. It has been termed by many a "failed star", even though the comparison would be akin to calling an asteroid "a failed Earth". As impressive as it is, extrasolar planets have been discovered with much greater masses. However, it is thought to have about as large a diameter as a planet of its composition can, as adding extra mass would only result in further gravitational compression (until ignition occurs). There is no clear-cut definition of what distinguishes a large and massive planet such as Jupiter from a brown dwarf, although the latter possesses rather specific spectral lines, but in any case it would need to be about seventy times as massive if it were to become a star.

Jupiter also has the fastest rotation rate of any planet within the solar system, resulting in a flattening easily seen through a telescope. Its best known feature is probably the Great Red Spot, a storm larger than Earth. The planet is perpetually covered with a layer of clouds.

Jupiter is usually the fourth brightest object in the sky (after the Sun, the Moon and Venus; however at times Mars appears brighter than Jupiter, while at others Jupiter appears brighter than Venus). It has been known since ancient 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' heliocentric theory of the motions of the planets; Galileo's outspoken support of the Copernican theory got him in trouble with the Inquisition.

Physical characteristics

Planetary composition

Jupiter is composed of a relatively small rocky core, surrounded by metallic hydrogen, surrounded by liquid hydrogen, which is surrounded by gaseous hydrogen. There is no clear boundary or surface between these different phases of hydrogen; the conditions blend smoothly from gas to liquid as one descends.

Atmosphere

Jupiter's atmosphere is composed of ~86% hydrogen and ~14% helium. By number of atoms, the atmosphere is ~75%/24% by mass; with ~1% of the mass accounted for by other substances - the interior contains denser materials such that the distribution is ~71%/24%/5%. The atmosphere contains trace amounts of methane, water vapour, ammonia, and "rock". There are also negligible amounts of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, and sulfur. The outermost layer of the atmosphere contains crystals of frozen ammonia.

This atmospheric composition is very close to the composition of the solar nebula. Saturn has a similar composition, but Uranus and Neptune have much less hydrogen and helium.

Jupiter's upper atmosphere undergoes differential rotation, an effect first noticed by Cassini (1690). The rotation of Jupiter's polar atmosphere is ~5 minutes longer than that of the equatorial atmosphere. In addition, bands of clouds of different latitudes flow in opposing directions on the prevailing winds. The interactions of these conflicting circulation patterns cause storms and turbulence. Wind speeds of 600 km/h are not uncommon. A particularly violent storm, about three times Earth's diameter, is known as the Great Red Spot.

The only spacecraft to have visited Jupiter's atmosphere is the Galileo probe, which dropped a lander into the planet in July 1995. The lander parachuted through 150 km of the atmosphere, collecting data for 58 minutes, before being crushed by the extreme pressure to which it was subjected. It would have then quickly melted and vaporized. Galileo itself underwent a more rapid version of the same fate when it was deliberately crashed into the planet on September 21, 2003 at a speed of over 50 km per second, in order to avoid any possibility of it crashing into and possibly contaminating one of the Jovian moons.

Planetary rings

Jupiter has a faint planetary ring system composed of smoke-like dust particles knocked off of its moons by meteor impacts. The main ring is made of dust from the satellites Adrastea and Metis. Two wide gossamer rings encircle the main ring, originating from Thebe and Amalthea. There is also an extremely tenuous and distant outer ring that circles Jupiter backwards. Its origin is uncertain, but this outer ring might be made of captured interplanetary dust.

See also: Rings of Jupiter.

Magnetosphere

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. Jupiter's magnetosphere is the largest structure in the solar system.

The Pioneer probes confirmed the existence that Jupiter's enormous magnetic field is 10 times stronger than Earth's and contains 20,000 times as much energy. The sensitive instruments aboard found that the Jovian magnetic field's "north" magnetic pole is at the planet’s geographic south pole, with the axis of the magnetic field tilted 11 degrees from the Jovian rotation axis and offset from the center of Jupiter in a manner similar to the axis of the Earth's field. The Pioneers measured the bow shock of the Jovian magnetosphere to the width of 26 million kilometres (16 million miles), with the magnetic tail extending beyond Saturn’s orbit.

The data showed that the magnetic field fluctuates rapidly in size on the sunward side of Jupiter because of pressure variations in the solar wind, an effect studied in further detail by the two Voyager spacecraft. It was also discovered that streams of high-energy atomic particles are ejected from the Jovian magnetosphere and travel as far as the orbit of the Earth. Energetic protons were found and measured in the Jovian radiation belt and electric currents were detected flowing between Jupiter and some of its moons, particularly Io.

Exploration of Jupiter

Jupiter has been known of since ancient times and is visible to the naked eye in the night sky. In 1610, Galileo Galilei discovered the four largest moons of Jupiter using a telescope, the first observation of moons other than Earth's.

A number of probes have visited Jupiter.

Pioneer flyby missions

Pioneer 10 flew past Jupiter in December of 1973, followed by Pioneer 11 exactly one year later. They provided important new data about Jupiter's magnetosphere, and took some low resolution photographs of the planet.

Voyager flyby missions

Voyager 1 flew by in March 1979 followed by Voyager 2 in July of the same year. The Voyagers vastly improved our understanding of the Galilean moons and discovered Jupiter's rings. They also took the close up images of the planet's atmosphere.

Galileo orbiter

The Galileo probe went into orbit around Jupiter in 1995, 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 in 1994, giving a unique vantage point for this spectacular event. In September, 2003 its mission ended as it burned up in Jupiter's upper atmosphere.

Cassini flyby mission

In 2000, the Cassini probe, en route to Saturn, flew by Jupiter and provided some of the highest-resolution images ever made of the planet.

Future probes

After the discovery of a liquid ocean on Jupiter's moon Europa, NASA is planning a mission dedicated to the icy moons. The JIMO, or Jupiter Icy Moons Orbiter, is expected to be launched sometime after 2012.

In 2007, Jupiter will also be briefly visited by the New Horizons probe, en route to Pluto.

Jupiter's moons

Jupiter has at least 63 moons. For a complete listing of these moons, please see Jupiter's natural satellites. For a timeline of their discovery dates, see Timeline of natural satellites.

The four large moons, known as the "Galilean moons", are Io, Europa, Ganymede and Callisto.

Galilean moons

The orbits of Io, Europa and Ganymede form a pattern known as a 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 receives an extra tug from its neighbors 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.

Classification of Jupiter's moons

It used to be thought that Jupiter's moons were arranged neatly into four groups of four, but recent discoveries of many new small outer moons have complicated the division; there are now thought to be six main groups, although some are more distinct than others.

1. The inner group of four small moons all have diameters of less than 200 km, orbit at radii less than 200,000 km, and have orbital inclinations of less than half a degree.
2. The four Galilean moons were all discovered by Galileo Galilei, orbit between 400,000 and 2,000,000 km, and include some of the largest moons in the solar system.
3. Themisto is in a group of its own, orbiting halfway between the Galilean moons and the next group.
4. The Himalia group is a tightly clustered group of moons with orbits around 11-12,000,000 km from Jupiter.
5. The Carme group is a fairly distinct group that averages 23,404,000 km from Jupiter with an average inclination of 165 degrees.
6. The Ananke group is a group with rather indistinct borders, averaging 21,276,000 km from Jupiter with an average inclination of 149 degrees.
7. The Pasiphaë group is a disperse and only vaguely distinct group that covers all the outermost moons.

It is thought that the 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.

Cometary impact

During the period July 16 to July 22, 1994, over twenty fragments from the comet Shoemaker-Levy 9 hit Jupiter's southern hemisphere, providing the first direct observation of a collision between two solar system objects. It is thought that due to Jupiter's large mass and location near the inner solar system it receives the most frequent comet impacts of the solar system's planets.

Jupiter in fiction and film

• Jupiter is the setting of Stanley Kubrick's classic film 2001: A Space Odyssey (1968), although the novel of the same name by Sir Arthur C. Clarke is set in the Saturnian system instead. In both the book and the film of the sequel, 2010: Odyssey Two (1984), fictional technology converts Jupiter into a star by increasing the density of its core.
• Both Arthur C. Clarke's novella A Meeting with Medusa (1988) and his novel 2010 depict journeys into the depths of Jupiter's atmosphere, where vast, city-sized floating life-forms have evolved.
• Ben Bova's novel Jupiter (2001) also features a journey into Jupiter's clouds and the discovery of life there.
• In the Star Trek universe, Jupiter is home to Jupiter Station.
• The role-playing game Jovian Chronicles features a solar nation, the Jovian Confederacy , in a series of space colony cylinders called "Gray Viarium" colonies around Jupiter.
• The novels of Kim Stanley Robinson, including The Memory of Whiteness, Green Mars and Blue Mars depict numerous ideas about the future colonization of Jupiter, although they focus more on the moons than on the planet itself.
• The plot of the anime Martian Successor Nadesico revolves around a mysterious invasion force based on Jupiter, named the "Jovian Lizards", or simply the "Jovians", and the attempts of the earth's forces, and specifically the ship Nadesico, to subdue this invasion.
• Jupiter is an important location in The Night's Dawn Trilogy by Peter F. Hamilton. This is where the first Bitek habitat was germinated and Edenism began.

External links

Wikimedia Commons has multimedia related to Jupiter (planet) .

• NASA's Jupiter fact sheet http://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html
• A Trip Into Space http://www.vias.org/spacetrip/jupiter_1.html Data and photos on Jupiter