Jupiter

**Jupiter** is the fifth planet from the Sun and the largest in the solar system. Jupiter and the other gas giants—Saturn, Uranus, and Neptune—are sometimes referred to as Jovian planets. It also accounts 70 percent of the total mass of all planets combined. Its atmosphere is denser than Earth, which is eight times thicker than Earth. Closer towards its core, there is a layer of liquid hydrogen, as well as, crystallization transforms this layer into oxygen. It's surface temperature of Jupiter is -145 degrees Celsius. However, this gas giant planet could not become a red dwarf star. Despite its size, it does not have the critical mass required for the process of nuclear energy creation. According to impression Jupiter's mass is, extrasolar planets have been discovered with much greater masses. Currently, if an object is above 12 Jupiter masses, large enough to burn deuterium, it is considered a brown dwarf; below that mass, it is a planet.

## Overview

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.

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 a volume 1300 times that of Earth. Quite naturally, Jupiter's gravitational influence has dominated the evolution of the solar system: most planets' orbits lie closer to Jupiter's orbital plane than the Sun's equatorial plane (Mercury is the only planet which is closer to the Sun's equator in orbital tilt), the majority of short-period comets belong to Jupiter's family (a result due to both Jupiter's mass and its relative speed), the Kirkwood gaps in the asteroid belt are mostly due to Jupiter, and Jupiter is even thought to have been possibly responsible for the late heavy bombardment of the inner solar system's history. Some have described the solar system as consisting of the Sun, Jupiter, and assorted debris. Some describe Jupiter as the solar system's vacuum cleaner, due to its immense gravity well.

Jupiter also has the fastest rotation rate of any planet within the solar system, making a complete rotation on its axis in slightly less than ten hours, which results in an equatorial bulge easily seen through an Earth-based amateur telescope. Jupiter is perpetually covered with a layer of clouds, composed of ammonia crystals and possibly ammonium hydrosulphide, and it may not have any solid surface in that the density may simply increase gradually as you move towards the core. Its best known feature is the Great Red Spot, a storm larger than Earth which was likely first observed by Giovanni Domenico Cassini and Robert Hooke four centuries ago. Indeed, mathematical models suggest that the storm is stable and may be a permanent feature of the planet. In 2000, three small spots merged to form a larger spot named Oval BA, which later acquired a red hue very similar to that of the Great Red Spot.

## Historical observations

Jupiter has been known since ancient times and is visible to the naked eye in the night sky. The Romans named the planet after the Roman god Jupiter (also called Jove). The astronomical symbol for the planet is a stylized representation of the god's lightning bolt. The Chinese, Korean, Japanese, and Vietnamese refer to the planet as the *wood star*, 木星, based on the Chinese Five Elements (curiously enough, through a small telescope, it does somewhat resemble a circular slice of wood in appearance, with the Red Spot being a "knot"). In Vedic Astrology, Hindu astrologers refer to Jupiter as "Guru" which means the "Wise One".

In 1610, Galileo Galilei discovered the four largest moons of Jupiter, Io, Europa, Ganymede and Callisto (now known as the Galilean moons) using a telescope, the first observation of moons other than Earth's. This was also 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 placed him under the threat of the Inquisition.

The pope had issued an official statement, or bull, declaring that the earth was the center of the universe. When Galileo studied the writings and theorems of Copernicus, and compared the theorems to observations of movements observed by his telescope, Galileo declared that the Copernican theory appeared to be correct, the earth revolves around the sun. This placed the church in a position of embarrassment and therefore declared Galileo a heretic. In 1892, E. E. Barnard observed a fifth satellite of Jupiter with the 36-inch refractor at Lick Observatory in California. The discovery, a testament to his extraordinary eyesight, made him quickly famous. The moon was later named Amalthea.

## Great Red Spot phenomena

The best known feature of Jupiter is the Great Red Spot, a persistent anticyclonic storm located 22° south of the equator. The Great Red Spot is first discovered and existed since 1665. It produces wind-speeds up to 432 km/h (268 mph). The recorded observations from 1665 to 1713 are believed to be of the same storm; if this is correct, it has existed for at least 356 years. It was next observed in September 1831, with 60 recorded observations between then and 1878 when continuous observations began. Its diameter is three times larger than Earth and it is largest, longest-lived storm in the Solar System. Based on the recorded and captured discoveries, it could change the size of the storm. It's spectroscopic appearance is due to composition of phosphorus, created when turbulent gases in the upper atmospheric layer react to the sunlight.

## Physical characteristics

### Planetary composition

Jupiter is composed of a relatively small rocky core, surrounded by metallic hydrogen, surrounded by liquid molecular hydrogen, which is surrounded by gaseous hydrogen. There is no clear boundary or hard 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 ~90% hydrogen and ~10% 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 vapor, ammonia, and "rock". There are also traces of carbon, ethane, hydrogen sulphide, neon, oxygen, phosphine, and sulphur. The outermost layer of the atmosphere contains crystals of frozen ammonia. Through IR and UV measurements benzene at a relative mixing rate of 2x10-9 to hydrogen and other hydrocarbons have also been found. 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 Giovanni 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, known as tropical regions 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. The only spacecraft to have plunged into Jupiter's atmosphere to take scientific measurements is the *Galileo* probe (see Galileo mission). It sent an atmospheric probe into Jupiter upon arrival in 1995, then itself entered Jupiter's atmosphere and burned up in 2003. The next mission to study the atmosphere in detail is the Juno mission, scheduled for launch in June 2010 for Jupiter.

## Exploration

### Pioneer flyby missions

Pioneer 10 flew past Jupiter in December of 1973, followed by Pioneer 11 exactly one year later. Pioneer 10 made the first ever close up images of Jupiter, studied its atmosphere, and detected its magnetic field.

### Voyager flyby missions

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

### Ulysses flyby mission

In February 1992, *Ulysses* solar probe performed a flyby of Jupiter at a distance of 450,000 km (6.3 Jovian radii). The flyby was required to attain a polar orbit around the Sun. The probe conducted studies on Jupiter's magnetosphere. Since there are no cameras onboard the probe, no images were taken. In February 2004, the probe came again in the vicinity of Jupiter. This time the distance was much greater, about 240 million km.

### Galileo mission

So far the only spacecraft to orbit Jupiter is the *Galileo* orbiter, which went into orbit around Jupiter on December 7 1995. It orbited the planet for over seven years and conducted multiple flybys of all of the Galilean moons and Amalthea. The spacecraft 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. However, while the information gained about the Jovian system from the *Galileo* mission was extensive in its own right, its originally-designed capacity was limited by the failed deployment of its high-gain radio transmitting antenna.

An atmospheric probe was released from the spacecraft in July, 1995. The probe entered the planet's atmosphere in December 7 1995. It parachuted through 150 km of the atmosphere, collecting data for 57.6 minutes, before being crushed by the extreme pressure to which it was subjected. It would have melted and vaporized shortly thereafter. The *Galileo* orbiter itself experienced a more rapid version of the same fate when it was deliberately steered into the planet on September 21, 2003 at a speed of over 50 km/s, in order to avoid any possibility of it crashing into and possibly contaminating Europa, one of the Jovian moons.

### 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

NASA is planning a mission to study Jupiter in detail from a polar orbit. Named *Juno*, the spacecraft is planned to launch by 2010.

Because of the possibility of a liquid ocean on Jupiter's moon Europa, there has been great interest to study the icy moons in detail. A mission proposed by NASA was dedicated to study them. The JIMO (Jupiter Icy Moons Orbiter) was expected to be launched sometime after 2012. However, the mission was deemed too ambitious and its funding was canceled.

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

## Natural satellites

Jupiter has at least 79 moons. For a complete listing of these moons, please see Jupiter's natural satellites. For a timeline of their discovery dates, see Timeline of discovery of Solar System planets and their natural satellites. The four large moons, known as the "Galilean moons", are Io, Europa, Ganymede and Callisto.

The orbits of Io, Europa, and Ganymede, the largest moon in the solar system, 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. There is a table of the four Galilean moons below:

(km)
(kg)
(days)
 Europa
 Ganymede
 Callisto

## See also

* List of Gas Giants
* Great red spot
* Comet Shoemaker Levy 9