Jupiter
Weather systems on Earth blow themselves out in a few days or weeks. On the solar system's giant planets, though, weather systems can last for decades. The record holder is Jupiter's Great Red Spot, which was first observed no later than 1830 -- and perhaps a good bit earlier. This oval storm system is wide enough to swallow two Earths, and the winds at its perimeter blow several times faster than the strongest hurricane ever recorded on Earth.
View in 2009
The Great Red Spot (upper right) is wide enough to swallow two Earths.
As the Great Red Spot demonstrates, Jupiter is a world of superlatives. It is the largest planet in the solar system (big enough to swallow more than 1,300 Earths, and bigger than some types of stars), and more massive than the solar system's other known planets and moons combined. It rotates faster than any other planet, it produces the most powerful magnetic field, and it offers the largest and most interesting assortment of moons.
Despite its great size and its brightness in Earth's night sky, however, much about Jupiter remains poorly understood. Scientists must infer quite a bit about it from observations by the spacecraft that have visited the planet.
Much of the mystery surrounds Jupiter's interior. From the planet's mass, density, and magnetic field, scientists surmise that it probably has a dense core of rock and metal at least 10 times as massive as Earth. A thick layer of hydrogen surrounds the core. Jupiter's gravity squeezes this layer so tightly that it acts as a metal. The metallic hydrogen probably rotates at a different speed from the core, so it produces a "dynamo" effect, generating electric currents that create Jupiter's magnetic field.
Layers of hydrogen and helium gas surround the metallic hydrogen, and a relatively thin layer of clouds envelops the entire planet. (This layer is actually dozens of miles thick, but compared to Jupiter's great size, that's like the skin on an onion.) Jupiter's rapid rotation stretches the clouds into narrow bands that circle the entire planet.
The bands show different colors, which means their clouds are made of different materials and hover at different altitudes. The highest layers of clouds, which are white, are made of frozen ammonia. Clouds in the next layer contain ammonia mixed with other chemicals, so they look brown or orange. The lowest layers contain water vapor and water ice, so they look blue.
These bands form alternating light and dark stripes. The light-colored stripes are decks of clouds that are pushed high into the atmosphere by rising bubbles of warm gas. The darker stripes consist of cooler material that is dropping back into the planet's atmosphere.
Much of the weather in these zones draws its energy not from the Sun, as is the case with storms on Earth, but from deep within Jupiter itself. As Jupiter's gravity squeezes the planet, it produces heat that wells up through the atmosphere then escapes into space as infrared energy. Jupiter radiates more energy into space than it receives from the Sun.
Rings encircle Jupiter, although they are far darker and skimpier than those of the flashier planet Saturn. The rings may consist of material that was "sandblasted" off the surfaces of Jupiter's moons by collisions with meteorites.
Since Jupiter has no solid surface, no human will ever walk on the planet. In fact, any attempt to visit the Jovian system will require heavy shielding. Jupiter's magnetic field captures electrically charged particles from the Sun and from the planet's volcanic moon Io. These particles create strong radiation belts. Around Io's orbit, the radiation belts are powerful enough to kill an unprotected human in a few minutes. That adds one more item to the list of Jupiter's superlatives: deadliest radiation belts.
View in 2009
The largest planet in our solar system is a commanding presence for much of the year. It looks like an intensely bright cream-colored star, shining brighter than anything else in the night sky except the Moon and Venus. It climbs into view in the pre-dawn sky in February. It rises earlier as the months go by, and moves into the evening sky in late spring. Jupiter is at opposition in mid-August, when it appears brightest for the year and remains visible all night. Late in the year it is visible only in the evening sky, dropping lower each night.
Jupiter's Moons
1. Metis
2. Adrastea
3. Amalthea
4. Thebe
5. Io
6. Europa
7. Ganymede
8. Callisto
9. Themisto
10. Leda
11. Himalia
12. Lysithea
13. Elara
14. S/2000 J11
15. Iocaste
16. Praxidike
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17. Harpalyke
18. Ananke
19. Isonoe
20. Erinome
21. Taygete
22. Chaldene
23. Carme
24. Pasiphae
25. S/2002 J1
26. Kalyke
27. Magaclite
28. Sinope
29. Callirrhoe
30. Euporie
31. Kale
32. Orthosie
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33. Thyone
34. Euanthe
35. Hermippe
36. Pasithee
37. Eurydome
38. Aitne
39. Sponde
40. Autonoe
41. S/2003 J1
42. S/2003 J2
43. S/2003 J3
44. S/2003 J4
45. S/2003 J5
46. S/2003 J6
47. S/2003 J7
48. S/2003 J8
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49. S/2003 J9
50. S/2003 J10
51. S/2003 J11
52. S/2003 J12
53. S/2003 J13
54. S/2003 J14
55. S/2003 J15
56. S/2003 J16
57. S/2003 J17
58. S/2003 J18
59. S/2003 J19
60. S/2003 J20
61. S/2003 J21
62. S/2003 J22
63. S/2003 J23
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Keywords
Galileo to Jupiter
Jupiter
Jupiter's Great Red Spot
Jupiter's Moons
Planetary Rings
Voyager Probes
This document was last modified: May 04, 2009
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