JUPITER, THE MISSED STAR

The jovian system in an artistic composition  (JPEG, 34 K) (NASA-JPL)

We have no direct information as to the internal composition of Jupiter or the source of the irradiated heat, but we can consider this gigantic planet as a missed star, a body that did not aggregate enough material to trigger the nuclear reactions and "switch itself on" as it happened for the Sun.
Jupiter has 6 satellites, the most important and famous of which are the 4 medicean moons discovered by Galileo: Io, Europa, Ganymede and Callisto. Io is the nearest to the planet, while Ganymede is the largest. The day on Jupiter last a little less than 10 hours, and such fast rotation is one of the causes of the turbulence and vortexes that can be observed in the jovian atmosphere.
The most visible formation on the surface is the Great Red Spot, a vast oval zone at a considerable height in the atmosphere of Jupiter.

A comparison between Jupiter and the Earth. The diameter of Jupiter is over 11 times that of the Earth and its volume over 1,400 times larger. The atmospheric circulation of the two planets is considerably different: in fact, the terrestrial cloud configuration is dominated by spiral cyclones, while Jupiter has a basic configuration based on zones with large cyclonic systems and oval shaped anti-cyclones (JPEG, 240 K) (NASA-JPL)

 

The passage of the satellite Io, and its shadow on the jovian disc, in a picture of Hubble Space Telescope. As the other gaseous giants, Saturn, Uranus and Neptune, Jupiter does not have a solid surface but, due to the huge pressures it undergoes, it could have in the centre a liquid phase or even a nucleus of metallic Hydrogen.  (JPEG, 30 K) (NASA-STScI)

 

The Great Red Spot, a huge cyclonic system as large as 12,000x25,000 km, compared with the size of the Earth in this picture taken by the Galileo probe. This could be the highest point of the cyclone, an ascending mass of gas that carries materials to the surface from the depth of the planet. It was observed probably for the first time by Dominique Cassini in the 17th century.  (JPEG, 53 K) (NASA-JPL)

 

The four galilean satellites are actual worlds on the planetary scale. In this composite picture taken by Voyager 1, you can see them in their correct size, just as they would appear at a distance of approximately un million km. Even the relative colours and the reflectivity have been exactly respected. From top left, clockwise: Io, Europa, Callisto and Ganymede. (JPEG, 35 K) (NASA-JPL)

 

Three images of the whole disc of the volcanic moon Io, taken by the Galileo spacecraft in June 1996. The colours have been intensified to increase the details of the surface. Compared to the images of the Voyager, 17 years ago, at least a dozen vast regions have been covered by layers of new volcanic material.  (JPEG, 413 K) (JPL)

 

The satellite Io in a picture taken by the Galileo probe in June 1996. In the upper rectangle, a picture of 1979 taken by Voyager, for a comparison. Ra Patera is a 40,000 square km area where the surface underwent remarkable changes. You can also see a new eruption that spreads for approximately 100 km in space. The blue colour of the plume is due to the presence of sulphuric dioxide gas, and snow that is condensing from the gas. The eruption of Ra Patera shines in the darkness, maybe due to the   fluorescence of the ions emitted in the highly energetic environment of the jovian  magnetosphere.  (JPEG, 23 K) (NASA-JPL)

 

Two aspects of one of the hemispheres of Europa, the icy jovian satellite. On the left, in natural colours, on the right in artificially highlighted colours to point out the different structures of the crust made of ice and water. The brown-dark areas represent rocky material that came from the inner layers, that emerged due to impacts with external bodies, or maybe a combination of external and internal material. The long black lines are fractures of the crust, some of them can be 3,000 km long. Europa has a diameter of approximately 3,160 km. This picture was taken on September 7th 1996 by from the Galileo spacecraft, at a distance of 677,000 km.  (JPEG, 74 K) (NASA-JPL)

 

Close up of Callisto, the less geologically active satellite among the medicean objects. Apparently, the impact craters are the only geological process that moulded the surface. This picture shows a resolution of approximately 10 km. The most evident detail is the ancient impact basin Valhalla, a luminous central region 600 km large, surrounded by a configuration of brilliant concentric rings. As Ganymede, Callisto is 50% ice.  (JPEG, 56 K) (NASA-JPL)

 

Ganymede is the most geologically complex satellite. It is composed of water, ice and rocky materials, and probably the low melting point of the ice allowed this body, which is relatively small, to have a very active geological history. This view from Voyager 2 of the hemisphere of Ganymede that faces Jupiter is dominated by the ancient dark plain called Galileo Regio.  (JPEG, 55 K) (NASA-JPL)

 

Stereoscopic image of the Galileo Regio zone on Ganymede. New topographic details are visible in this computer restoration of two images taken from the Galileo probe in Summer 1996 at a distance of 10,220 km. The colour of the sky at the horizon is artificial.  (JPEG, 449 K) (NASA-JPL)

 

An extraordinary event is illustrated in this image of the fragments of the Shoemaker-Levy comet while it approaches Jupiter. The impacts happened on the dark side of Jupiter a few minutes before its fast rotation brought the impact areas to our observation.  (JPEG, 46 K) (NASA-STScI)

 

Picture of July 1994 of eight impact zones, on Jupiter, of the Shoemaker-Levy comet, that broke into 20 fragments by the tidal force of the planet. The fragments fell one after the other in the jovian atmosphere, causing "spots" with halos that extended for thousands of km. The dark material was prevalently composed of methane.  (JPEG, 239 K) (NASA-STScI)

 

This infrared picture of the impact of the H fragment of Shoemaker-Levy on Jupiter was obtained with the 3.6 m ESO telescope at La Silla (Chile). The developed temperature was measured: it was over 27 degrees centigrade, almost 200 degrees higher than that of the surrounding atmosphere, while the luminosity was 50 times higher than that of the jovian disc.  (JPEG, 238 K) (ESO)

 

The impact of the last fragment of the Shoemaker-Levy comet on Jupiter. A sequence at different wavelengths taken by Hubble Space Telescope, on July 22nd, 1994, shows the rising and subsequent collapse of the plume created by the impact of the W fragment.  (JPEG, 102 K) (NASA-STScI)

Among the various instruments placed on board the probe that detached from the Galileo spacecraft on December 7th 1995 to explore the jovian atmosphere, there is a detector of the Helium abundance, build in Germany, which determined a value of approximately 24%. Such date, very similar to that of the Sun, tells us that Jupiter maintained the primordial gaseous composition.
 
 

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