Jupiter's Moons

Key points: Captured moons; Galilean moon properties; interiors of the Galilean moons and how they formed

Jupiter has 16 - no, now 63!! - moons that may be subdivided into three groups
  • The innermost four with orbits closer to Jupiter than Io's. These moons are small and irregular in shape
  • Four large "Galilean" Satellites
  • Small outer moons that appear to form two groups; the moons in each group have nearly the same average distance from Jupiter suggesting that they are broken apart asteroids captured by Jupiter. More of this type are being discovered all the time, causing the total known number to climb rapidly

A picture of Amalthea, the best-known inner moon, is to the right, and a movie of how it would look from a spaceship is hereen00500_1.jpg (18578 bytes) (from Galileo Project)

amalthe5.jpg (6420 bytes)
This animation shows all the moons in orbit around Jupiter, which is in the center. You can see the inner moons in regular orbits and how much farther away from Jupiter the rest are. This distribution emphasizes how most of the moons are captured into orbits where they are only loosely held. (from Tony Dunn, Gravity Simulator, http://www.orbitsimulator.com/gravity/articles/joviansystem.html)


jovianmoons.gif (404393 bytes)

Galilean Moons

            Galilean moons montage

In order of distance from Jupiter:



Io, full disk

Volcano Loki erupting on Io's limb

A volcano on Io

From Galileo mission, http://www.jpl.nasa.gov/galileo/images/images.html

Artist's concept of being on the surface of Io Artist's impression of surface of Io (William Hartmann)


Europa, full disk view


Surface features on Europa

More European surface features

(From Galileo Mission, http://www.jpl.nasa.gov/galileo/images/images.html)

Close up showing "freeze marks" on Europa

A closeup (smallest features about 10km across).

From Galileo mission, http://www.jpl.nasa.gov/galileo/images/images.html

Artist's concept on the surface of Europa Artist's concept on the surface of Europe (version 2) Two artist's impressions of the surface of Europa (Don Dixon)



largest moon in the solar system; Ganymede is larger than Mercury

  • surface shows many more craters and is darker than Europa's implying that its surface is much older. The dark color comes from meteorite dust.
  • Recent Galileo orbiter results suggest that the surface may be divided into plates much like the Earth's surface
ganymede.jpg (28837 bytes)
Young terrain on Ganymede  

Left: different terrains on Ganymede. Can you tell which area is younger? (hint: count craters)

From Galileo mission, http://www.jpl.nasa.gov/galileo/images/images.html

Older terrain on Ganymede
Artist's impression from the surface of Ganymede Artist's impression of the surface of Ganymede (Don Dixon)


From Galileo mission, http://www.jpl.nasa.gov/galileo/images/images.html

callisto.jpg (45875 bytes) callisto_surface.jpg (189114 bytes)
callisto_asgaard.jpg (87109 bytes) Artist's impression from the surface of Callisto


The interiors of Io, Europa, Callisto, and Ganymede, clockwise from upper left. All except Callisto have metallic (iron/nickel) cores, shown in gray, surrounded by rock in brown. The rock shells in Europa and Ganymede are surrounded by liquid water (blue) and ice (white). Callisto is shown as an undifferentiated mixture of ice and rock. (from John Brodholt, http://slamdunk.geol.ucl.ac.uk/~brodholt/) galmoonint.jpg (80183 bytes)

Notice the pattern in properties of the Galilean moons with increasing distance from Jupiter:

This trend mimics the trend in properties of planets with distance from the Sun. The properties of the moons indicate that they formed as small objects around a large one, with similar consequences to the formation of the (relatively) small planets around the much larger sun. A combination of heating by the central object and the larger energy of collisions due to the high orbital velocities close to it can account for these trends in both cases.

saturn-shani1.gif (23682 bytes)Shani, Vedic god of Saturn, http://www.payer.de/kommkulturen/kultur123.htm

sirtflaunch.jpg (4413 bytes)


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Huygen's drawing explaining the various aspects of the rings of Saturn. http://www.surveyor.in-berlin.de/himmel/Bios/Huygens-e.html

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hypertext copyright.jpg (1684 bytes) G. H. Rieke

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