Solar system

Final fact

You could stuff 1,300 Earths into Jupiter

Saturn

Much like its neighbor Jupiter, the sixth planet from the sun has a rocky core and a gaseous surface. But Saturn is chiefly known for its intricate series of rings that encircle it. The mile-thick rings are made of countless orbiting ice particles, from less than an inch to several feet in size.

Up close, it's clear that Saturn has more rings than we can count. But though you can't see all of them from Earth, you can spot three of them with a good telescope,.

The two outermost rings are separated by a dark band called the Cassini

Division, named for the astronomer who discovered it in 1675. The Cassini division isn't empty, but it has less material in it. The middle ring is the brightest, and just inside it is a fuzzy one that can be difficult to spot.

Saturn has 18 known satellites, made mostly of ice and rock. The largest,

Titan, orbits Saturn every 16 days and is visible through a good-sized amateur telescope. Titan, which is larger than the planet Mercury, has a thick atmosphere that obscures its surface. Though researchers aren't sure how many moons Saturn has, the total is likely at least 20, and may be much higher.

Historical notes

When Galileo Galilei first studied Saturn in the early 1600s, he thought it was an object with three parts. Not knowing he was seeing a planet with rings, the stumped astronomer entered a small drawing -- a symbol with one large circle and two smaller ones -- in his notebook, as a noun in a sentence describing his discovery. Debate raged for more than 40 years about these "ears," until Christiaan Huygens proposed that they were rings.

Giovanni Domenico Cassini later discovered a gap between the rings, which gained his name, and he also proposed that the rings were not solid objects, but rather made of small particles.

Uranus

The seventh planet from the sun is much like its gaseous neighbors, with a cloudy surface, rapid winds, and a small rocky core.

URANUS: PERSONIFICATION OF HEAVEN IN ANCIENT MYTHPerhaps because of a collision with a large object long ago, Uranus orbits at an extreme tilt of 98 degrees -- sort of on its side. This causes one pole to point toward the sun for decades, giving the planet strange seasons.

Uranus has numerous satellites and a faint set of rings. If all the possible satellites being studied are confirmed, Uranus would have 16 regular and five irregular moons, making it the most populated planetary satellite system known. Saturn is known to have 18 satellites (there may be more, but they have not been well-documented).

Historical notes

Uranus was thought to be a star until William Herschel discovered in 1781 that it orbited the Sun.

Neptune

The eighth planet from the Sun -- well, some of the time it's eighth, but more on that later -- has a rocky core surrounded by ice, hydrogen, helium and methane.Like the other gas planets, Neptune has rapidly swirling winds, but it is thought to contain a deep ocean of water. Its quick rotation fuels fierce winds and myriad storm systems. The planet has a faint set of rings and 8 known moons.

Because of Pluto's strange orbit, Neptune is sometimes the most distant planet from the Sun. Since 1979, Neptune was the ninth planet from the Sun.

On February 11, 1999, it crossed Pluto's path and once again become the eighth planet from the Sun, where will remain for 228 years.