Moving almost twice as far from the Sun as we were at Saturn, to just over 19 astronomical units, we reach the planet Uranus. It is classified as an ice giant rather than a gas giant. Its interior contains large amounts of water, methane and ammonia. Uranus has 28 known moons and 13 known rings.

One remarkable characteristic is that Uranus's axis is tilted about 98 degrees. Earth's tilt, which drives our seasons, is only 23½ degrees, so Uranus is essentially spinning on its side. Astronomers speculate that this extreme tilt may be the result of collisions with one or more large objects early in the Solar System's history.

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