Jupiter (astronomy) - Overview, Historical observations, Physical characteristics, Exploration of Jupiter, Natural satellites, Life on Jupiter, Trojan asteroids

The fifth major planet from the Sun, and the innermost of the giant outer planets. It contains two-thirds of the matter in the Solar System, apart from the Sun. It has been observed in close-up by five space probes: Pioneer 10 and 11, Voyagers 1 and 2, and Galileo. Its basic characteristics are: mass 1·90 × 10²⁷ kg; equatorial radius 71 492 km/44 423 mi; polar radius 66 854 km/41 541 mi; mean density 1·33 g/cm³; rotational period 9 h 55 min 41 s; orbital period 11·9 years; inclination of equator to orbit 3·1°; mean distance from the Sun 5·203 AU. It is made primarily of hydrogen (82%) and helium (17%), and believed to have an innermost core of terrestrial composition of 5–10 Earth masses, a large outer core of hydrogen and helium in a metallic phase, a liquid hydrogen/helium mantle, and a deep gaseous atmosphere. The planet has a significant internal source of heat, and radiates twice as much heat from inside as it receives from the Sun.

The face of the planet is covered by clouds, organized into bands, called belts and zones. Zones are light, and cold (?130°C) because they are high in the atmosphere; belts are darker and warmer clouds (?40°C) at a lower elevation; and a third, warmer level of clouds has also been observed (20°C). The uppermost clouds are inferred to be solid ammonia, the middle clouds ammonium hydrosulphide, and the lowest clouds water. The rotation period in the equatorial region is 5 min faster than that of the rest of the planet - a differential which contributes to the formation of a richly coloured banded structure in the cloudy atmosphere. Complex currents and vortices are observed within the bands, including a long-lived atmospheric storm called the Great Red Spot. The known Jovian moons (as of 2006) number 63, including the four large satellites discovered by Galileo (1610), which are distinct worlds in themselves and lie in near-circular orbits in an equatorial plane. A dark ring of dust around the planet was discovered by Voyager, between 100 000 and 215 000 km from the centre of the planet, consisting of material from the surface of Jupiter's four innermost moons.

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	4333.2867 d (11.86 a)
Synodic period	398.88 d
Avg. Orbital Speed	13.056 km/s
Max. Orbital Speed	13.712 km/s
Min. Orbital Speed	12.446 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 (11.209 Earths)
Polar diameter	133,709 km (10.517 Earths)
Oblateness	0.064 87
Surface area	6.14 ×10 (120.5 Earths)
Volume	1.431 ×10 (1321.3 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)
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
Adjective	Jovian
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	<0.00010%

Jupiter (IPA: /ˈdʒuːpɪtə/) is the fifth planet from the Sun and the largest within the solar system.

Overview

Jupiter is usually the fourth brightest object in the sky (after the Sun, the Moon and Venus);

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). Quite naturally, Jupiter's gravitational influence has dominated the evolution of the solar system: some have described the solar system as consisting of the Sun, Jupiter, and assorted debris. 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 the planet may have been responsible for the Late Heavy Bombardment of the inner solar system's history.

As impressive as Jupiter's mass is, extrasolar planets have been discovered with much greater masses. This has led some astronomers to term it a "failed star" -- although Jupiter would need to be about seventy-five times as massive to become a star, the smallest red dwarf is only about 30% larger than Jupiter. When it was younger and hotter, Jupiter was much larger than it is today, though previously Saturn would have been even bigger than Jupiter due to its lower mass: Saturn has a much weaker gravitational pull and with more heat, both planets would have been more bloated (and because of Saturn's lower core mass, this effect would have been greater).

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.

Historical observations

The planet Jupiter has been known 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, Io, Europa, Ganymede and Callisto (now known as the Galilean moons) using a telescope, the first observation of moons other than Earth's.

Physical characteristics

Planetary composition

Jupiter is composed of a relatively small rocky core, surrounded by metallic hydrogen, with further layers of liquid hydrogen and gaseous hydrogen.

Atmosphere

Jupiter's atmosphere is composed of ~90% hydrogen and ~10% helium by number of atoms.

The only spacecraft to have descended 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.

See also: Cloud pattern on Jupiter

The Great Red Spot

The Great Red Spot is a persistent anticyclonic storm on the planet Jupiter, 22° south of the equator, which has lasted at least 340 years.

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 9.2 million km (5.7 million miles) from Jupiter.

Planetary rings

Jupiter has a faint planetary ring system composed of smoke-like dust particles knocked from its moons by energetic meteor impacts. Metis orbits within its fluid Roche limit with Jupiter, and objects not rigidly attached to it may freely fall away from it and into Jupiter's gravitational field. 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(one of Jupiter's moon).

The Pioneer probes confirmed that Jupiter's enormous magnetic field is 10 times stronger than Earth's and contains 20,000 times as much energy.

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.

Exploration of Jupiter

A number of probes have visited Jupiter. Pioneer 10 obtained the first ever close up images of Jupiter and the Galilean moons, studied its atmosphere, detected its magnetic field, observed its radiation belts and found that Jupiter is mainly liquid.

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).

Galileo mission

So far the only spacecraft to orbit Jupiter is the Galileo orbiter, which went into orbit around Jupiter on December 7, 1995.

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. It will pass through the Jupiter system at 21 km/s (47,000 mph), with closest approach to Jupiter occurring at approximately 06:00 UTC February 28, 2007.

Future probes

NASA is planning a mission to study Jupiter in detail from a polar orbit.

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.

Natural satellites

Jupiter has at least 63 moons.

The Galilean moons, compared to Earth's moon Luna
Name (Pronunciation key)		Diameter (km)	Mass (kg)	Orbital radius (km)	Orbital period (days)
Io	eye'-oe ˈaɪəʊ	3643 (105% Luna)	8.9×1022 (120% Luna)	421 700 (110% Luna)	1.77 (6.5% Luna)
Europa	ew-roe'-pə jʊˈrəʊpə	3122 (90% Luna)	4.8×1022 (65% Luna)	671 034 (175% Luna)	3.55 (13% Luna)
Ganymede	gan'-ə-meed ˈgænəmid	5262 (150% Luna)	14.8×1022 (200% Luna)	1 070 412 (280% Luna)	7.15 (26% Luna)
Callisto	kə-lis'-toe kəˈlɪstəʊ	4821 (140% Luna)	10.8×1022 (150% Luna)	1 882 709 (490% Luna)	16.69 (61% Luna)

Classification of Jupiter's moons

Before the discoveries of the Voyager missions, Jupiter's moons were arranged neatly into four groups of four. A basic division is between the eight inner regular moons with nearly circular orbits near the plane of Jupiter's equator, which are believed to have formed with Jupiter, and an unknown number of small irregular moons, with elliptical and inclined orbits, which are believed to be captured asteroids or fragments of captured asteroids.

Life on Jupiter

It is considered highly unlikely that there is any Earth-like life on Jupiter, as there is little water in the atmosphere and any possible solid surface deep within Jupiter would be under extraordinary pressures.

Trojan asteroids

In addition to its moons, Jupiter's gravitational field controls numerous asteroids which have settled into the regions of the Lagrangian points preceding and following Jupiter in its orbit around the sun.

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.