Saturn
The planet Saturn is a delicate giant. Although it is the second largest planet in the solar system, it's the least dense -- less dense than water. Chemical compounds in its upper atmosphere color its cloud bands in subtle shades of ivory, yellow, and tan. And broad, lacy rings encircle Saturn, making it the most beautiful planet in the solar system.
View in 2009
Like its larger sibling, Jupiter, Saturn is a ball of hydrogen and helium gas wrapped around a dense, rocky core. Saturn spins so fast that it bulges outward at the equator, so the planet is much thicker at the equator than through the poles.
Saturn’s clouds are colored in subtle shades of yellow and
tan.
Saturn's rapid rotation and its layered structure produce a magnetic field. Observations by the Cassini spacecraft suggest that the field may be changing, which could mean that Saturn's interior is changing as well. Cassini monitored radio waves produced by the magnetic field as a way to measure Saturn's rotation rate. (Because Saturn has no solid surface, it's impossible to measure its rotation by tracking surface features like mountains or canyons.) But the craft found that the rotation rate appeared to have slowed by about six minutes since the Voyager missions two decades earlier. Scientists believe that Saturn is not actually slowing down. Instead, one possible explanation says that changes in the planet's core are creating changes in the magnetic field.
Saturn's clouds contain ammonia, methane, and other toxic compounds. They are buffeted by winds of up to 1,000 miles (1,600 km) per hour, and they contain violent storm systems that produce lightning blasts a million times more powerful than those on Earth.
Saturn's most prominent feature, though, is its extensive ring system.
Galileo Galilei discovered the rings in the early 17th century. In his small, crude telescope, though, they looked like "bumps" on the side of the planet. Five decades later, Dutch astronomer Christaan Huygens, who had recently discovered Saturn's largest moon, Titan, detected a bit of space between Saturn and the bumps. He deduced that the bumps were really planet-circling rings.
Today, astronomers know that thousands of individual rings make up Saturn's ring system. Some rings are made of small bits of frozen water, others contain tiny grains of dust, and still others are a mixture of the two. In all, the rings are only a few hundred feet thick. Several small moons orbit inside or just outside the ring system. These "shepherd" satellites help keep the ring particles in place, but they also sculpt some rings into odd shapes, with twists and kinks.
Saturn's rings probably formed when a small moon or a comet passed close to Saturn and was pulled apart by the planet's gravity.
French mathematician Edward Roche first described this process around 1850. A planet's gravity pulls more strongly on the side of a moon that is facing it than on the side that is away from it. If a moon passes too close to its parent planet, this difference, called tidal gravity, pulls it apart, turning the moon into cosmic rubble. Over time, the rubble spreads out to form rings -- like those that encircle Saturn.
Although Saturn has no solid surface to stand on, humans may someday view its rings from close range. They may walk on some of its icy moons or even float above Saturn's clouds in big balloons. From such a lofty vantage point, the rings would form wide, sparkling bands across the sky. Sometimes, icy particles from the inner edge of Saturn's rings may fall into the planet's atmosphere, creating bright "shooting stars" as they streak through the sky of this delicate giant.
View in 2009
Saturn looks like a bright golden star. It spends the first eight months of the year in Leo, the lion, then moves into the neighboring constellation Virgo, the virgin. Saturn is at its best in early March, when it's closest to Earth. It disappears behind the Sun in late August, then returns to view in the morning sky in October.
Saturn's Moons
1. Albiorix
2. Atlas
3. Calypso
4. Daphnis
5. Dione
6. Enceladus
7. Epimetheus
8. Erriapo
9. Helene
10. Hyperion
11. Iapetus
12. Ijiraq
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13. Janus
14. Kiviuq
15. Mimas
16. Methone
17. Mundilfari
18. Paaliaq
19. Narvi
20. Pan
21. Pallene
22. Pandora
23. Phoebe
24. Polydeuces
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25. Prometheus
26. Rhea
27. Siarnaq
28. Skadi
29. Suttung
30. Tarvos
31. Telesto
32. Tethys
33. Thrym
34. Titan
35. Ymir
36. S/2004 S7
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37. S/2004 S8
38. S/2004 S9
39. S/2004 S10
40. S/2004 S11
41. S/2004 S12
42. S/2004 S13
43. S/2004 S14
44. S/2004 S15
45. S/2004 S16
46. S/2004 S17
47. S/2004 S18
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Keywords
Cassini to Saturn
Pioneer Probes
Saturn
Saturn's Atmosphere
Saturn's Moons
Saturn's Rings
This document was last modified: May 04, 2009
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