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With its numerous moons and several rings,
the Jupiter system is a "mini-solar system." Jupiter
is the most massive planet in our solar system, and
in composition it resembles a small star. In fact, if
Jupiter had been between fifty and one hundred times
more massive, it would have become a star rather than
a planet.
On January 7, 1610, while skygazing from
his garden in Padua, Italy, astronomer Galileo Galilei
was surprised to see four small "stars" near Jupiter.
He had discovered Jupiter's four largest moons, now
called Io, Europa, Ganymede, and Callisto. Collectively,
these four moons are known today as the Galilean satellites.
Galileo would be astonished at what we
have learned about Jupiter and its moons in the past
30 years. Io is the most volcanically active body in
our solar system. Ganymede is the largest planetary
moon and has its own magnetic field. A liquid ocean
may lie beneath the frozen crust of Europa. An icy ocean
may also lie beneath the crust of Callisto. In 2003
alone, astronomers discovered 21 new moons orbiting the giant planet. Jupiter now officially
has 61 moons - by far the most in the solar system.
Many of the outer moons are probably asteroids captured by the giant planet's gravity.
At first glance, Jupiter appears striped.
These stripes are dark belts and light zones created
by strong east-west winds in Jupiter's upper atmosphere.
Within these belts and zones are storm systems that
have raged for years. The southern hemisphere's Great
Red Spot has existed for at least 100 years, and perhaps
longer, as Galileo reported seeing a similar feature
nearly 400 years ago. Three Earths could fit across
the Great Red Spot. Jupiter's core is probably not solid
but a dense, hot liquid with a consistency like thick
soup. The pressure inside Jupiter may be 30 million
times greater than the pressure at Earth's surface.
As Jupiter rotates, a giant magnetic field
is generated in its electrically conducting liquid interior.
Trapped within Jupiter's magnetosphere - the area in
which magnetic field lines encircle the planet from
pole to pole - are enough charged particles to make
the inner portions of Jupiter's magnetosphere the most
deadly radiation environment of any of the planets,
both for humans and for electronic equipment. The "tail"
of Jupiter's magnetic field - that portion stretched
behind the planet as the solar wind rushes past - has
been detected as far as Saturn's
orbit. Jupiter's rings and moons are embedded in an
intense radiation belt of electrons and ions trapped
in the magnetic field. The Jovian magnetosphere, which
comprises these particles and fields, balloons one to
three extending more than one billion kilometers behind
Jupiter - as far as Saturn's orbit.
Discovered in 1979 by NASA's Voyager 1
spacecraft, Jupiter's rings were a surprise: a flattened
main ring and an inner cloud-like ring, called the halo,
are both composed of small, dark particles. A third
ring, known as the gossamer ring because of its transparency,
is actually three rings of microscopic debris from three
small moons: Amalthea, Thebe, and Adrastea. Jupiter's
ring system may be formed by dust kicked up as interplanetary
meteoroids smash into the giant planet's four small
inner moons. The main ring probably comes from the tiny
moon Metis.
In December 1995, NASA's Galileo spacecraft
dropped a probe into Jupiter's atmosphere. Carrying
six scientific instruments, the probe survived the crushing
pressure and searing heat for nearly an hour, collecting
the first direct measurements of Jupiter's atmosphere,
the first real data about the chemistry of a gas planet.
Following the release of the probe, the Galileo spacecraft
began a multi-year orbit of Jupiter, observing each
of the largest moons from close range several times.
Related Links:
Source: NASA
Last Updated : 08.20.2003
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Distance from the Sun:
(Semimajor axis of orbit)
778,412,010 km
5.20336301 A.U.
Radius:
71,492 km
(11.209 of Earth's radius)
Volume:
1316 (Earth = 1)
Mass:
1,898.7 x 1027 g
Density:
1.33 gm/cm3
Surface Gravity:
2312 cm/s2
Escape Velocity:
59.54 km/s (at equator)
Sidereal Rotation Period:
0.41354 day
Sidereal Orbit Period:
11.862615 sidereal years
Mean Orbit Velocity:
13.0697 km/s
Orbit Eccentricity:
0.04839266
Orbit Inclination:
1.30530 degrees
Equatorial Inclination:
3.12 degrees
Mean Surface Temperature:
288 to 293 K
Atmospheric Temperature (at
level with pressure = 1 bar):
165 K
Major Atmospheric Constituents:
H2, He
Natural Satellites:
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
17. Harpalyke
18. Ananke
19. Isonoe
20. Erinome
21. Taygete
22. Chaldene
23. Carme
24. Pasiphae
25. S/2002 J1
26. Kalyke
27. Megaclite
28. Sinope
29. Callirrhoe
30. Euporie
31. Kale
32. Orthosie
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
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
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