Saturn

True_Saturn

Adorned with thousands of beautiful ringlets, Saturn is unique among the planets. All four gas giant planets have rings — made of chunks of ice and rock — but none are as spectacular or as complicated as Saturn’s. Like the other gas giants, Saturn is mostly a massive ball of hydrogen and helium.

Saturn was the most distant of the five planets known to the ancients. In 1610, Italian astronomer Galileo Galilei was the first to gaze at Saturn through a telescope. To his surprise, he saw a pair of objects on either side of the planet. He sketched them as separate spheres, thinking that Saturn was triple-bodied. Continuing his observations over the next few years, Galileo drew the lateral bodies as arms or handles attached to Saturn. In 1659, Dutch astronomer Christiaan Huygens, using a more powerful telescope than Galileo’s, proposed that Saturn was surrounded by a thin, flat ring. In 1675, Italian-born astronomer Jean-Dominique Cassini discovered a division between what are now called the A and B rings. It is now known that the gravitational influence of Saturn’s moon Mimas is responsible for the Cassini Division, which is 4,800 km (3,000 miles) wide.

Like Jupiter, Saturn is made mostly of hydrogen and helium. Its volume is 755 times greater than that of Earth. Winds in the upper atmosphere reach 500 m (1,600 feet) per second in the equatorial region. (In contrast, the strongest hurricane-force winds on Earth top out at about 110 m, or 360 feet per second.) These super-fast winds, combined with heat rising from within the planet’s interior, cause the yellow and gold bands visible in the atmosphere.

In the early 1980s, NASA’s Voyager 1 and Voyager 2 spacecraft revealed that Saturn’s rings are made mostly of water ice, and they imaged “braided” rings, ringlets and “spokes” — dark features in the rings that circle the planet at different rates from that of the surrounding ring material. Saturn’s ring system extends hundreds of thousands of kilometers from the planet, yet the vertical depth is typically about 10 m (30 feet) in the main rings. During Saturn’s equinox in autumn 2009, when sunlight illuminated the rings edge-on, Cassini spacecraft images showed vertical formations in some of the rings; the particles seem to pile up in bumps or ridges more than 3 km (2 miles) tall.

Saturn’s largest moon, Titan, is a bit bigger than the planet Mercury. (Titan is the second-largest moon in the solar system; only Jupiter’s moon Ganymede is bigger.) Titan is shrouded in a thick, nitrogen-rich atmosphere that might be similar to what Earth’s was like long ago. Further study of this moon promises to reveal much about planetary formation and, perhaps, about the early days of Earth. Saturn also has many smaller icy satellites. From Enceladus, which shows evidence of recent (and ongoing) surface changes, to Iapetus, with one hemisphere darker than asphalt and the other as bright as snow, each of Saturn’s satellites is unique.

Though Saturn’s magnetic field is not as huge as Jupiter’s, it is still 578 times as powerful as the Earth’s. Saturn, its rings and many of its satellites lie totally within Saturn’s own enormous magnetosphere — the region of space in which the behavior of electrically charged particles is influenced more by Saturn’s magnetic field than by the solar wind. While the Hubble Space Telescope imaged Saturn’s aurora in the ultraviolet, the Cassini spacecraft found that Saturn has a unique secondary aurora at the north pole, imaged in the infrared in 2008. Aurorae occur when charged particles spiral into a planet’s atmosphere along magnetic field lines. On Earth, these charged particles come from the solar wind. Cassini showed that at least some of Saturn’s aurorae are like Jupiter’s and are largely unaffected by the solar wind.

The next chapter in our knowledge of Saturn is being written right now by the Cassini mission, which carried Europe’s Huygens probe to Saturn. The Huygens probe descended through Titan’s atmosphere in January 2005, collecting data on the atmosphere and surface. The Cassini spacecraft, orbiting Saturn since 2004, continues to explore the planet and its moons, rings and magnetosphere. By July 2009, Cassini had returned more than 200,000 images. The Cassini Equinox Mission is studying the rings during Saturn’s autumnal equinox, when the sun shines directly on Saturn’s equator. Three-dimensional features are visible in the rings during this time of year, such as moonlets that protrude above and below the ring plane and cast shadows, revealing their sizes and shapes.

Natural color view of Saturn's rings. Image from NASA.
Natural color view of Saturn’s rings. Image from NASA.

 

 

Icy Dione, one of Saturn's moons, enriched by the tranquil gold and blue hues of Saturn. NASA
Icy Dione, one of Saturn’s moons, enriched by the tranquil gold and blue hues of Saturn. NASA
Discovered By
Known by the Ancients
Date of Discovery
Unknown
Orbit Size Around Sun (semi-major axis)
Metric: 1,426,666,422 km
English: 886,489,415 miles
Scientific Notation: 1.4266664 x 109 km (9.53667594 A.U.)
By Comparison: 9.537 x Earth
Perihelion (closest)
Metric: 1,349,823,615 km
English: 838,741,509 miles
Scientific Notation: 1.34982 x 109 km (9.023 A.U.)
By Comparison: 9.176 x Earth
Aphelion (farthest)
Metric: 1,503,509,229 km
English: 934,237,322 miles
Scientific Notation: 1.50351 x 109 km (1.005 x 101 A.U.)
By Comparison: 9.885 x Earth
Sidereal Orbit Period (Length of Year)
29.447498 Earth years
10,755.70 Earth days
By Comparison: 29.447 x Earth
Orbit Circumference
Metric: 8,957,504,604 km
English: 5,565,935,315 miles
Scientific Notation: 8.958 x 109 km
By Comparison: 9.530 x Earth
Average Orbit Velocity
Metric: 34,701 km/h
English: 21,562 mph
Scientific Notation: 9.6391 x 104 m/s
By Comparison: 0.324 x Earth
Orbit Eccentricity
0.05386179
By Comparison: 3.223 x Earth
Orbit Inclination
2.49 degrees
Equatorial Inclination to Orbit
26.7 degrees
Mean Radius
Metric: 58,232 km
English: 36,183.7 miles
Scientific Notation: 5.8232 x 104 km
By Comparison: 9.1402 x Earth
Equatorial Circumference
Metric: 365,882.4 km
English: 227,348.8 miles
Scientific Notation: 3.65882 x 105 km
By Comparison: 9.1402 x Earth
Volume
Metric: 827,129,915,150,897 km3
English: 198,439,019,647,006 mi3
Scientific Notation: 8.2713 x 1014 km3
By Comparison: 763.594 x Earth
Mass
Metric: 568,319,000,000,000,000,000,000,000 kg
Scientific Notation: 5.6832 x 1026 kg
By Comparison: 95.161 x Earth
Density
Metric: 0.687 g/cm3
By Comparison: 0.125 x Earth
Surface Area
Metric: 42,612,133,285 km2
English: 16,452,636,641 square miles
Scientific Notation: 4.2612 x 1010 km2
By Comparison: 83.543 x Earth
Surface Gravity
Metric: 10.4* m/s2
English: 34.3 ft/s2
By Comparison: If you weigh 100 pounds on Earth, you would weigh about 107 pounds on Saturn (at the equator). *Derived from a 1 bar radius of 60,268 km.
Escape Velocity
Metric: 129,924 km/h
English: 80,731 mph
Scientific Notation: 3.609 x 104 m/s
By Comparison: Escape velocity of Earth is 25,030 mph.
Sidereal Rotation Period (Length of Day)
0.444 Earth days
10.656 hours
By Comparison: 0.445 x Earth
Effective Temperature
Metric: -178 °C
English: -288 °F
Scientific Notation: 95 K
Atmospheric Constituents
Hydrogen, Helium
Scientific Notation: H2, He
By Comparison: Earth’s atmosphere consists mostly of N2 and O2.