Triton Fun  

Facts about Jupiter



Jupiter is the largest planet in our solar system.    This dynamic colorful world is a very different kind of planet than the Earth.    Our planet is a solid world that you can stand on.   Jupiter, on the other hand, is a mostly gaseous world composed primarily of hydrogen and helium with smaller quantities of other materials.

This beautiful planet contains swirling clouds of gases in a banded structure.  The bands next to each other rotate in opposite directions which creates shear zones and fantastic meteorology.   Jupiter also sports a Great Red Spot, noted in its atmosphere for 300 years or more.    It is a gigantic storm swirling and roiling endlessly and causing chemical reactions to create the intense colors.

Jupiter has been visited by 8 spacecraft.  These were Pioneer 10, Pioneer 11, Voyager 1 and 2, Galileo, Ulysses, Cassini and New Horizons.  The very first mission to explore Jupiter was Pioneer 10, an American spacecraft launched in 1972.  This was a true pioneering mission in that, before it left Earth, no one knew whether spacecraft could travel through the asteroid belt between here and Jupiter and survive the trip.   

Pioneer 10 showed that the path to Jupiter was not as dangerous as the environment of Jupiter itself.   Getting through the asteroid belt was easy; surviving the powerful radiation in the Jupiter system (that would fry a human in minutes, and is damaging to spacecraft) is harder. 

Pioneer 10 and 11 spacecraft visited Jupiter in 1973 and 1974 and gave us the first close-up pictures of Jupiter and its moons.  They also provided a wealth of other data, including magnetic and ion particle data that helped us understand the magnetic field and magnetospheric ions and electrons encircling Jupiter.    (See our "Facts about Mars" page showing a table with information about all of the successful NASA missions to the planets).

The two Voyager spacecraft explored Jupiter in 1979 and sent back an astonishing collection of pictures of the planet and its moons.   It also returned data from other instruments that studied the infrared and ultraviolet spectra of the planet as well as the energetic particles in the Jupiter magnetosphere and the chemistry and physics of the atmosphere.

Galileo was the first Jupiter orbiter which, starting in 1995,  made close flybys of Jupiter's moons and found, for example, that most of the moons have their own magnetic fields  (something never before found on any other moon in the solar system). 

In particular, Ganymede has a magnetic field that has closed loops in it so that parts of its surface are protected from incoming radiation from Jupiter's magnetosphere.   Therefore, these areas on the surface (which are at the equator) have a somewhat different chemistry than the polar regions on Ganymede.  At the poles, the ions are focused into the surface, similar to the way radiation streams down Earth's magnetic field lines near our poles, hitting the atmospheric molecules and causing the "northern lights"  (aurorae).

The Cassini spacecraft did a flyby of Jupiter in 2000 while it was on its way to Saturn.  Since Galileo was still operating, the 2 spacecraft were able to do observations in tandem while both were in the neighborhood of Jupiter.   Cassini was able to make movies of Jupiter since it had a much higher data rate than the Galileo spacecraft;  these wonderful movies showed the swirling colorful atmosphere as it circulated around Jupiter and thus contributed to the scientific harvest.

The New Horizons spacecraft, on its way to Pluto, did a flyby of Jupiter in February 2007 in order to get a gravity boost.  It is currently sending back spectacular images of Jupiter and its moons.   Volcanoes going off on Io, bright surfaces on Europa, craters on Callisto, colorful patches on Ganymede, all have been imaged in the last few months.  It is a very exciting mission that is adding to our knowledge of the Jovian system.    See the New Horizons website for updates:

These spacecraft studied many aspects of the planet and its moons.  The moons are also referred to as satellites.   The explorations uncovered information about the atmosphere, satellites and magnetosphere of Jupiter and the data return was a rich harvest of spectra, photos and other measurements that scientists are still studying to understand this complex system.

The exploration of Jupiter by the 8 spacecraft has revolutionized our understanding of that system and also of the other planets and solar systems in general.

   Pioneer 10

These spacecraft studied many aspects of the planet and its moons.  The moons are also referred to as satellites.   The explorations uncovered information about the atmosphere, satellites and magnetosphere of Jupiter and the data return was a rich harvest of spectra, photos and other measurements that scientists are still studying to understand this complex system.



           Some facts about Jupiter :

  •  Jupiter is big !    Its diameter is 88,846 miles across.     It is big enough to fit 1000 Earths inside it. 
  •  Jupiter is radiating 1.9 times the heat it receives from the Sun.  This means it is generating its own heat.   This is caused by the  continual contraction of Jupiter that has been going on since its formation, as well as diffusive separation of gases,  radionuclides and other sources.

  •  Jupiter is 5 times farther from the Sun than Earth is.   The Earth is one “astronomical unit” from the Sun, that is, about 93,000,000 miles.  Jupiter is, therefore, 5 astronomical units from the Sun, specifically, it is ~ 483,700,000 miles from the Sun.    The Sun would look much smaller at Jupiter than it does to us here on Earth.

  • The temperature in the cloud tops of Jupiter is about -230 degrees Fahrenheit.

  • The amount of helium in Jupiter is very similar to that in the Sun.


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  • Powerful bolts of lightning occur in the clouds of Jupiter.   The energy of this lightning can be detected by spacecraft as crackling static in the radio signal.

  •  Jupiter has no solid surface as we know it.    The gaseous hydrogen in its atmosphere gets more and more dense as one moves down into the planet until the enormous pressures convert it into “liquid metallic hydrogen”, a material that only exists in laboratories on Earth and in the interiors of planets.    You could not walk on Jupiter; you could float in its clouds with a balloon but not land on a surface.

  • Jupiter has a ring around it.   It is so faint that it was not until the Voyager spacecraft visited it in 1979 that the ring was detected.   It is extremely thin and is made up of dark dust particles.

  • The magnetosphere of Jupiter (that is, its magnetic field and its environment) is enormous.  The field lines stretch out so far (because of their interaction with the Sun’s particles) that they reach all the way to the orbit of the Earth (we may be being bathed in Jupiter radiation right now!)


  • The inner magnetosphere of Jupiter is an intense radiation field.  The magnetic field lines have charged particles such as ions and electrons stuck on them and traveling with them as they circle Jupiter.  The charged particles impact the trailing sides of the satellites which causes chemical changes in their surfaces.



  • The four large satellites of Jupiter are Io, Europa, Ganymede and Callisto.    Each of these satellites have a complex and interesting chemistry, geology and physics on their surfaces and interiors.   Studies of these worlds (which are around the same size as our Moon) have expanded our understanding of surface geology processes and planetary formation.


               Picture of Io, Jupiter's volcanic moon


    • Io has extremely strong electrical currents running through it.   This arises from the volcanic gases getting ionized and then the ions that were created getting attached to Jupiter’s magnetic field lines.   There is a torus (donut-shaped) electrical field running through Io that is also linked to Jupiter.   Millions of amps of current run through Io as a result of these fields.



    •  Jupiter is a radio station !   It puts out radio emissions that are so strong, they can be detected on Earth.   The Pioneer and Voyager spacecraft were able to receive Jupiter’s radio signals.  These signals appear to come from deep inside of Jupiter and are thought to correlate with the rotation of Jupiter.   The length of the Jupiter day (that is, how long it takes to rotate once on its axis) is measured from this radio signal.   One cannot use the clouds of Jupiter to measure this since they float around the planet but are not tied to a “surface”.)



    • Jupiter’s satellites are fascinating worlds in their own right.  These are Io, Europa, Ganymede and Callisto and a host of smaller satellites.  The Galileo spacecraft found that Ganymede has its own magnetic field.  This was the first satellite to have a magnetic field which means it has magnetic field lines coming out of it which deflect charged particles such as electrons and ions when they come near Ganymede.   The magnetic field even protects certain regions on Ganymede from being hit by ions in Jupiter’s magnetic field.

    • The surfaces of the satellites all show different geologic histories:





            Geologic Map of Io showing volcanic calderas ringed with red lava - colors are              

            from sulfur compounds and other materials deposited on the surface



                   Sodium emission from Io









  • Io is the most volcanically active world in the solar system (it’s even more active than the Earth !)   There are at least 8 active volcanoes spewing sulfur gases out of their vents daily.   These volcanic plumes put out millions of tons of material that ends up in Jupiter’s magnetosphere.

    Io puts out gases such as SO2 and H2S in its volcanic emissions.  These get dissociated and ionized by photons and solar wind particles into ions such as S+, S++, O+, O+ and other ions with higher valence states.  These ions flow around with the magnetic field; some of them diffuse inwards towards Jupiter.  The ions trapped on the field lines impact the satellites on their trailing sides.  The ions then get implanted into the surface of the satellites and cause chemical and physical reactions, such as darkening and “gardening” of these surfaces.   These effects can be seen in the spectra of the satellites taken by spacecraft or by observers using Earth-based telescopes. 


What is the red spot of Jupiter made of ?   This is a good question that scientists are currently studying and many would like to know the answer to.   The current ideas are that the red color of the Great Red Spot and the browns and yellows and other colors of the clouds come from chemical compounds of sulfur and phosphorus.  The colors also arise from differential scattering of some wavelengths of visible light by particles in the Red Spot and in the atmosphere.    This is much like what happens in Earth’s atmosphere where certain wavelengths of light are scattered and give us the blue sky at daytime and a reddish sky at dusk.


    • Oceans !    It is thought that the interiors of Europa, Ganymede and Callisto have salty oceans beneath their icy surfaces.   Scientists can tell this from the measurements of the deflection of the spacecraft when they flew by as well as the change in Jupiter’s magnetic field near the satellites.    Some scientists think that the ocean is just a few miles below the surface and that one could drill down to them and reach liquid !    Others think that the oceans are much deeper (perhaps hundreds of miles down).

    •   Io has an incredibly active surface.  Volcanoes on Io are spouting plumes of sulfurous gases all the time.   Its surface is very young, in that the lava from recent volcanic flows cooled and created the surface we see today

    • Europa’s surface is quite “young” as well, that is, it shows very few craters indicating that tectonic activity has occurred, moving around the icy materials, creating smoothed areas and erasing the craters that formed during the heavy bombardment of planets and moons that occurred at the beginning of the solar system’s formation.  

  • Ganymede also has had some tectonic activity; it has cratered and grooved terrain and fissures where liquid water emerges from the cracks and freezes out on the surface.  Also, rafts of ice were created, moved around and then frozen in place, giving a patchwork, jigsaw-puzzle-like appearance to its surface.   

      • Callisto has the most ancient surface, showing thousands of craters and no sign of geologic movement, having preserved the record of its early bombardment and cratering history.  

      • Amalthea, a smaller satellite of Jupiter, is the reddest object in the solar system.   It is still not known why it is so red but the color is related to the constant bombardment of radiation from Jupiter’s magnetic field.







    Image of Ganymede                         Ganymede's unusual geology                  Europa color image                       Europa's "ice rafts" -fascinating geology


    White spots are craters                   Criss-crossed folded layers of ice                                                                     still not fully understood






    Twisted sister : Europa's bizarre geology                      Callisto - full of craters                    Chains of craters on Callisto



  • The chemistry of the atmosphere of Jupiter is quite interesting and dynamic.  Jupiter’s atmosphere consists mostly of hydrogen and helium.   It also has smaller amounts of other chemical compounds

  • The list of chemicals and their chemical formulae includes: 


    •   hydrogen (H2)


    •  helium (He)

    • methane (CH4)

    • ammonia (NH3)

    • water (H2O)

    • hydrogen sulfide  (H2S)

    • neon (Ne)

    • krypton (Kr)

    •  argon (Ar)

    • xenon (Xe)

    • ammonium hydrosulfide (NH4SH )

    • disulfur (S2)


       elemental sulfur (S8)
    • germane (GeH4)

    • deuterated hydrogen (HD)

    • phosphine (PH3)

    • arsine (AsH3)

    • carbon monoxide (CO)

    • carbon dioxide (CO2)

    •  deuterated methane (CH3D)

    • ethane (C2H6)

    • acetylene (C2H2)

    •  methyl acetylene (CH3CCH)

    • benzene (C6H6)


        ** See our Triton Fun Science Newsletter for articles about Jupiter and its moons:


                                August  2006 issue:      Europa


                                January 2007 issue:     Jupiter in the telescope


             March  2007 issue:     Jupiter encounter photos from New Horizon spacecraft and Hubble Space Telescope !


              April  2007 issue:     More fabulous images of Jupiter and its exotic moons, including volcanic eruptions !




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    Last updated 11/9/08