Authors :

Olubummi AJANI, 15 years old ;

Larry COUCHY, 14 y.o. ;

David GUENEE , 27 y.o. ;

Arthur KANG, 14 y.o.

School :

Collège Edouard Manet

180, bd Gallieni

92390 Villeneuve-La-Garenne





Jupiter is the largest planet in the solar system. It is more massive than all other planets and moons in our solar system combined ! It’s a very interesting object because of his exceptional size, the history of its knowledge and the informations it could give us in order to better understand our own planet.

I - Description / Composition


Jupiter is the 5 th planet of the solar system : the mean distance from the Sun : 5,2 u.a. (778,3 x 10^6 km)

Situation of Jupiter in the Solar System

Numerical datas

Equatorial diameters  :

142 984 km.

Weight  :

1,899x10^28 kg.

Orbit  :

one " year " (the time made by Jupiter to run around its orbit) is about 11,8 years.

Rotation  :

one " day " (the period of rotation around itself) is about 9h 50 min.

Temperature  :

- 140 ° C (133 Kelvin)

Magnetic field  :

4 gauss

Chemical composition of the Jovian atmosphere

The jovian composition is very close to the solar composition.

78% dihydrogene (H2)

20% Helium

2% Methane (CH4)

and clouds of ammoniac (NH3), NH4SH and water (H2O).


II - An exceptional planet - comparison with Earth

Jupiter is a giant planet

Jupiter is the largest planet of the solar system.

Why largest ? Because of its size and of its weight. Compared to our planet, everything is giant with Jupiter ! Let’s compare with Earth.

Equatorial diameter 142 984 km (J) 11,2 x DT

Weight 2x10^28 kg (317 x MT)

Magnetic field 4 gauss (0,3 à 0,6 gauss pour la Terre)

But not only because of this features. Furthermore, this planet has the biggest speed of rotation around itself and the biggest number of satellites.

Comparison of the different sizes : the nine planets of the Solar system.

A " gas planet ", but not only…

There is no solid surface on Jupiter. It’s not like Mercury, Venus, Earth or Mars for example. Jupiter is called a " gas planet ", mainly composed by hydrogen and helium. This composition is close to the composition of stars or of the gas that exists at the beginning of the solar system.

A large ocean of liquid hydrogen may may lie under the clouds.

But there is also a solid core in the centre of Jupiter, which is probably 10 or 20 times larger than Earth !

Many satellites

There are 16 welll-known satellites around Jupiter. The most famous ones are called the Galilean Moons. They have been discovered by Galilee in 1610. This four moons can be compared to our Moon or to Mercury for example. They are from the same kind of bodies : same size and composed of rock and metal. Their names are : Io, Europe, Ganymede and Callisto.

Jovian ring system : a recent discovery

Recently, a very thin ring system has been discovered on photographs taken by spacecraft crossing Jupiter towards the end of the solar system, in 1979. It’s too much thin to be seen from Earth, compared to the rings of Saturn, for example.

A very important magnetic field

Jupiter, like Earth or the other giant planets (like Saturn) has an important magnetic activity. It is also active in radio wavelength (decametric). This activity has been discovered in 1955. It was the first ground-based observation of radio emission from a magnetized planet. Later, astronomers discovered such emissions from other planets, but only with spacecrafts. The radio activity of Jupiter is the only one that is enough strong to be received on Earth. Nowadays, radio astronomers are studying the jovian activity for example from radio observatory like Nançay in France.

III - Past and future of Jupiter

3.1 – Its formation

The formation of Jupiter has to be linked to the formation of the solar system, as with all other planet.

The solar system was born about 4.5 billion years ago, from the collapse of a big cloud of gas and ice, mainly composed by hydrogen and helium. The beginning of this story may have been the collision with another cloud or a shock wave that had disturbed the cloud.

Under the pull of gravity, the cloud has collapsed into a nebula, during about 100,000 years. In the centre (the denser part) of this nebula, a star was born : the Sun.

All around the newborn star, a disk of dust and gaz was still rotating. Small articles of the nebula combined and formed bigger particles. Finally, planets has been formed. Depending on the distance to the Sun, several sort of planets appeared :

  • inner planets, also called " planetesimals ", mainly made of rock and metal (e.g. Earth) ;
  • outer planets (giant planets), like Jupiter, mainly made of gaz. Jupiter was enough far from the Sun to be plenty of hydrogen and helium.

So the story of Jupiter, as for all other planet of the solar system, is linked to the story of the Sun and of the solar system.

3.2 – She might be a star, if…

If Jupiter had been larger (heavier as well), the temperature inside would have been higher and then Jupiter would have been born as a star, not as a planet. A star is an celestial object that generate its own energy by nuclear fusion. A planet is too small and too cold to have a nuclear activity and, compared to stars, are " cold ".

In the universe, it is quite common to find star systems with two stars. Most stars that we can see are doubles. We call them binary stars. So… maybe the solar system could have been different if Jupiter was a bigger… Actually, it’s not really " a bit bigger " because astronomers think that a celestial body should be between 15 and 80 times as large as Jupiter in order to be a star (it depends on different theories). But Jupiter is already about 300 times bigger than Earth. So Jupiter was the favourite candidate for the " Begin a Star " contest…

3.3 – The collision with the comet Shoemaker-Levy 9

It has been a very important event. It is very seldom to observe such collision between a comet and the largest planet of our solar system !

On 1994 July 16-22, several fragments of the comet Shoemaker-Levy 9 collided with the planet. Astronomers (Carolyn and Eugene Shoemaker and David Levy) discovered this comet one year before. Many amateur and professional astronomers observed the collision.

It gave us beautiful pictures. Furthermore, scientists learned and hope to learn more about the composition of comets and Jupiter and more about the physics of such impacts into planetary atmospheres.

3.4 – Historical development of the knowledge of Jupiter

Jupiter is known since the prehistory.

This celestial object was so important in the sky that it got the name of the mainest God of Roman mythology : Jupiter (known as Zeus to the Greeks).

In 1610, Galileo Galilei, with his first telescope, observed the four Moons (now called " galilean moons "). It is very important for the story of scientific ideas because it showed that the world beyond the moon was able to change. It was against theories of Aristote. And furthermore, it helped to proove Copernicus heliocentric theory.

In 1630, Zucchi and Bartoli observed some dark and light bands on Jupiter, that are clouds.

In 1664, Hooke observed a big red spot. Now, we know that it’s a vast storm, four times larger than our planet !

In 1955, Burke and Franklin discovered jovian radio emission from ground-based observatory.

In 1979, Voyager-1 has sent pictures from the unexpected rings of Jupiter.

The knowledge of Jupiter has been seriously improved since scientists have sent spacecrafts like Pioneer, Voyager or Galileo. The main way used to obtain information was spectroscopy, that gives information of chemical composition.

3.5 – Meteorology : the clouds and storms on Jupiter…

There is a huge hurricane-like storm system on Jupiter : the Great Read Spot. It is well-known by astronomers for over 300 years. It is quite easy to observe from Earth with a telescope.

Several systems of clouds have been observed. They are in rotation all around the planet at different speeds, depending on the latitude. The clouds systems may persist during several monthes. This is quite long, much longer than the storms we know on Earth.

Clouds are especially composed of methane (CH4), ammoniac (NH3) and other gas (PH3, C2H4, etc…). They appear at different altitudes, pressure, temperature. In this way, studying composition of clouds (by spectroscop) may give interesting informations on the structure of the jovian atmosphere.

Unlike on Earth, it’s on Sun energy but Jupiter's internal heat that may produce the weather in its upper atmosphere.

3.6 – Questions for the future…

Its satellites

Scientist hope to learn a lot from satellites of Jupiter. Geology of this solid moons are know very well-understood, and could help us to understand better our own planet.

Its meteorology

The meteorology of Jupiter is very complex and is not yet well understood. Understanding physics of jovian atmosphere may give us information in order to understand better our own atmosphere.

Its magnetic activity

A better understanding of the jovian magnetic activity could give us a better understanding of geo-magnetic field as well.

3.7 – The end of Jupiter and of the solar system

In about 5 billion years, the Sun – our star – will consume most of its available " fuel " (hydrogen) and begin to die. The Sun will begin a red giant and grow up until the orbit of Mars. After, it will decrease and turn into a cold white dwarf. Then Jupiter will not receive anymore energy from Sun and will become colder. It will get also colder when the internal heat will decrease too.

IV - How to obtain information from Jupiter ?

4.1. by optical observations

Most of the first pictures we had from Jupiter have been taken by optical observatories, that is not so difficult because Jupiter is very shiny object in the sky. But the atmosphere is always an obstacle for astronomers, because of the diming of light and the impossibility to observe in infrared, ultra-violet, etc…

We can use photographs taken from Hubble Space Telescope.

Photo of Jupiter from Hubble Space Telescope.



4.2. Observations radioastronomiques

By " listening " at radio wavelength, astronomers are able to get informations on magnetic jovian activity, because solar particles into jovian magnetic field create radio emission.

It is possible to make this kind of observations from ground-based observatories.

4.4. Spacecrafts

Since 1973, several spacecrafts has been launched towards Jupiter (but not only for this planet) : Pionneer 10 and 11, Voyager 1 and 2 and Galileo for example.

The informations they obtained were important because they carried photo cameras (optical cameras observing in several colours) and different kind of devices for spectrometry IR and UV, polarimetry, measurement of magnetic field, cosmical rays, radio waves…

V - Exercise

Look at this report and collect the following informations.

  1. What is the distance between the Sun and Earth ?
  2. What is the distance between the Sun and Jupiter ?
  3. The energy received from the sun decrease with the square of the distance to the sun.

  4. How many time less is the energy received from Jupiter compared to Earth ?



Jupiter is the biggest planet of the Solar system. Every of its features are huge compared to our " little solid planet ". It is so huge that it may have become a star if it was bigger.

Because of this exceptional features, it’s a very well known object, for over a long time. But it still has mysteries for scientists. And we’re discovering again a lot of new things about it, especially since the space conquest has begun.

It will surely give us a lot of new informations, that could help us to understand more about our own planet. So, that makes the big one and the little one are not so different.