Jupiter / Introduction

Jupiter is the giant of the Solar System. Seventy percent of the total mass of the planets is accumulated in Jupiter. From the earth, we only see its dense atmosphere, which is eight times thicker than the atmosphere of the earth.

Beneath this atmosphere we find a layer of liquid hydrogen. The massive pressure results in crystallization of the matter and the next layer closer to the core of theplanet is made of metallic hydrogen.Jupiter has a rocky core with a diameter of approximately 25,000 kilometers and very high temperatures (30,000 to 35,000 °C).

The temperature drops steadily towards the outer layers. In the upper cloud layer, it is as low as minus 150 °C.Jupiter reflects 1.7 times the amount of energy that it actually receives from the sun. The planet therefore produces energy but has been inhibitedfrom developing into a sun. Despite its enormous size, it simply lacks the mass for such an evolution. Jupiter is not only the largest but also the fastest of all the planets of our system. It completes a full rotation on its on axis in less than ten hours. This high velocity has a great influence on the structure of its atmospheric layers where bands of clouds appear, orbiting certain zones of the planet. There are approximately ten different such zones on each of the hemispheres of Jupiter (temperate, tropic and equatorial zones). These bands of cloud blow with an enormous speed of up to 500 kilometers per hour in the direction opposite to the planet’s rotation. They appear to be rather stable and long-lasting structures as they have only marginally changed since the first time they were observed about 50 years ago. The great rotation velocity is ultimately responsible for the strong magnetic field of Jupiter, which reaches as far as the orbit of Saturn. The atmosphere of the planet consists mainly of hydrogen and helium with traces of other gases such as methane and ammonia. One of the typical compounds found on Jupiter is phosphine (PH3), which smells like garlic. Jupiter therefore keeps vampires well away!

A particularly spectacular occurrence was observed in July of 1994. The cometShoemaker-Ley 9 broke up into several fragments which then impacted on Jupiter. These gigantic collisions caused huge explosions and their brightness outshone the brightness of Jupiter by a factor of 50.

Orbit of Jupiter

Jupiter completes one full revolution around the sun in 11.86 earth years. Its mean distance to the sun is 778 million kilometers and its orbit velocity is approximately 13.05 kilometers per second.

The orbit velocity of the earth is just about 30 kilometersper second.

Jupiter has a much greater rotational velocity than the earth (one complete rotation equals one day) and is actuallythe fastest of all the planets. It is accompanied by 16 satellites.

While the sidereal day of the earth is approximately 24 hours, it is only9 hours and 55 minutes on Jupiter. At certain times, it is therefore possible to observe a full Jupiter day from the earth within one clear night. The rotation axis of the giant planet is slightly inclined towards its orbit plane(3.1 degrees) compared with the inclination of the earth’s axis of 23.4 degrees towards its orbit plane. As a result of the high rotational velocity, the equators of Jupiter are slightly protruding.

Composition of Jupiter

Jupiter consists mainly of hydrogen. Its diameter at the equator is 143,000 kilometers. At its center there is a silicate core of approximately 25,000 kilometers in diameter and with an average temperature of 30,000 °C.

This core is covered in a layer ofionized hydrogen. This layer combined with the high rotational velocity ofthe planet create the strong magnetic field of Jupiter.

Between the layer of ionized hydrogen and the atmosphere thereis a thick layer of liquid hydrogen.

The atmosphere itself consists of90% hydrogen and 10% helium with traces of other compounds such as ammonia, methane and water.The dimensions of Jupiter are gigantic and the earth could be stored 1300 times within Jupiter .A further remarkable feature of Jupiter is the Great Red Spot, which is actually at the heart of an anticyclone storm. There are numerous white oval features to be observed on the planet that are also storm systems.

The Great Red Spot

The phenomenon of the Great Red Spot is visible on virtually all published photographs of Jupiter. It is the largest and longest persisting storm in the Solar System and described as an anticyclone.

The spot is suspended eightkilometers above the clouds covering Jupiter and its diameteris three times that of the earth.

The Great Red Spot was first observed more than 300 yearsago, although its nature was at that time unknown. The many drawings and photographs that were made of the phenomenon enable scientists today to establish that the spot has only slightly changed in size over the last 300 years.The red color of the spot appears to derive from phosphorus, which is produced when gases reach the outer atmosphere and react under the influence of sunlight. The Great Red Spot rotates about its own axis approximately 10 times a day and moves at a very slow and irregular pace around the planet.

How is it possible that such an immense storm can persist for such a long time? In contrast to the meteorological processes on the earth, new clouds on Jupiter are formed instantly. Clouds on the earth are built up slowly by the evaporation of water on the surface and it takes some time until the water that rained down in the previous storm has evaporated to form new ”Rain“ on Jupiter falls into a hot atmosphere where the drops evaporate instantly.

Jupiter Moons

Jupiter has a ring and sixteen moons. The four largest satellites are called the Galileans after the name of the discoverer. They are Io, Europa, Ganymede and Callisto.

All satellites are located outside Jupiter’s ring. Nearest to the ringare Adrastea and Metis, followedby Amalthea and Thebe. Then follow the Galileans and Leda, Himalia, Lysithea and Elara.

The four satellites farthest from Jupiter are called Ananke, Carme,Pasiphae and Sinope. These last fourmoons revolve around the planet in the opposite direction to the other satellites and the rotation of Jupiter itself. It has been suggested that they were originally planetoids , which were trappedby the planet.They are up to 24 million kilometers distant from Jupiter. With the exception of the Galileans that have dimensions comparable to the size of our moon or even larger, the moons of Jupiter are rather small objects with diameters of maximum 200 kilometers.

The Galileans are a particularly interesting group. Io has a distinct red and yellowish color deriving from sulphur erupting from volcanoes. The satellite is also heavily exposed to the magnetic field of Jupiter and charged particles are exchanged between Io and Jupiter. Io features the most active volcanoes in the Solar System. It has a diameter of 3640 kilometers and its distance from Jupiter is approximately 422,000 kilometers.

Europa as well as Io are rather young moons. On February 20th, 1997, the Galileo spacecraft took photographs of Europa that revealed most astonishing facts. The satellite is partly covered by an ocean with icebergs floating on it. The existence of liquid water other than on the earth had up to that time been considered highly unlikely. That the satellite is a rather young object was confirmed by the large number of meteor craters on Europa, which has a diameter of 3140 kilometers and is approximately 671,000 kilometers from Jupiter.
Ganymede is 1,070,000 kilometers from Jupiter and has a heavily cratered icy crust.

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