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1. Io
2. Europa
3. Ganymede
4. Callisto

5. Amalthea
6. Himalia
7. Elara
8. Pasiphae
9. Sinope
10. Lysithea
11. Carme
12. Ananke
13. Leda
14. Thebe
15. Adrastea
16. Metis
17. Callirrhoe
18. Themisto
19. Megaclite
20. Taygete
21. Chaldene
22. Harpalyke
23. Kalyke
24. Iocaste
25. Erinome
26. Isonoe
27. Praxidike
28. Autonoe
29. Thyone
30. Hermippe
31. Aitne
32. Eurydome
33. Euanthe
34. Euporie
35. Orthosie
36. Sponde
37. Kale
38. Pasithee
39. Hegemone
40. Mneme
41. Aoede
42. Thelxinoe
43. Arche
44. Kallichore
45. Helike
46. Carpo
47. Eukelade
48. Cyllene
49. Kore
50. S/2003 J2
51. S/2003 J3
52. S/2003 J4
53. S/2003 J5
54. S/2003 J9
55. S/2003 J10
56. S/2003 J12
57. S/2003 J15
58. S/2003 J16
59. S/2003 J17
60. S/2003 J18
61. S/2003 J19
62. S/2003 J23
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mercury Mercury
venus Venus
earth Earth
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jupiter Jupiter
saturn Saturn
uranus Uranus
neptune Neptune
pluto Pluto
Planet Stats
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Planets & Stars
A Light Year
Jupiter's Moons
Jupiter's Moons

To date, there have been 63 moons found orbiting Jupiter. The most famous of these are the Galilean moons: Io, Europa, Ganymede and Callisto, which were first seen by Galileo Galilei in 1610 using his crude 33-power telescope. When Galileo first saw these satellites of Jupiter, he realized that not everything in the Universe orbits around the Earth.

The planet Jupiter's four largest moons are called the Galilean satellites, after Italian astronomer Galileo Galilei, who observed them in 1610. The German astronomer Simon Marius claimed to have seen the moons around the same time, but he did not publish his observations and so Galileo is given the credit for their discovery. These large moons, named Io, Europa, Ganymede, and Callisto, are each distinctive worlds.

Jupiter Moon IOIo is the most volcanically active body in the solar system. It's surface is covered by sulfur in different colorful forms. As Io travels in its slightly elliptical orbit, Jupiter's immense gravity causes 'tides' in the solid surface 100 meters (300 feet) high on Io, generating enough heat to give rise to the volcanic activity and drive off any water. Io's volcanoes are driven by hot silicate magma.

EuropaEuropa's surface is mostly water ice, and there is evidence that it may be covering an ocean of water or slushy ice. Europa is thought to have twice as much water as does Earth. This moon intrigues astrobiologists because of its potential for having a 'habitable zone.' Life forms have been found thriving near subterranean volcanoes on Earth and in other extreme locations that may be similar to what may exist on Europa.


Ganymede is the largest moon in the Solar System. Completing an orbit in roughly seven days, it is the seventh moon and third Galilean moon from Jupiter. It is larger in diameter than the planet Mercury but has only about half its mass. It has the highest mass of all planetary satellites with 2.01 times the mass of the Earth's moon.

Ganymede is composed primarily of silicate rock and water ice. It is has an iron-rich, liquid core. A saltwater ocean is believed to exist nearly 200 km below Ganymede's surface, sandwiched between layers of ice. Its surface comprises two main types of terrain. Dark regions, saturated with impact craters and dated to four billion years ago, cover about a third of the satellite. Lighter regions, crosscut by extensive grooves and ridges and only slightly less ancient, cover the remainder. The cause of the light terrain's disrupted geology is not fully known, but was likely the result of tectonic activity brought about by tidal heating.

CallistoThe most distant of Jupiter's Galilean Moons, Callisto shows the highest density of impact craters in the Solar System, but harbors no volcanoes or even any large mountains. It is thought that the surface is billions of years old. The first hint that something interesting might be happening beneath the surface came from Galileo's measurements of Callisto's magnetic field. Dr. Krishan K. Khurana of UCLA and colleagues discovered that the magnetic field fluctuated in time with Jupiter's rotation. The best explanation was that Jupiter's powerful magnetic field was creating electrical currents somewhere within Callisto, and those currents in turn created a fluctuating magnetic field around Callisto.

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