What is the coldest planet?
Uranus has recorded the coldest temperatures of any planet, about −224°C (−371°F), even though Neptune is farther from the Sun.
Most planets give off more heat than they receive from the Sun, because of warmth left over from their formation. Uranus gives off very little extra heat, perhaps because of a giant collision long ago. As a result, its upper atmosphere is colder than Neptune's.
Uranus is an ice giant made mainly of water, ammonia and methane around a small rocky core. Methane in its atmosphere absorbs red light, giving it a pale blue-green color.
A planet on its side
Uranus is tilted about 98 degrees, so it rolls around the Sun on its side. Each pole gets about 42 years of continuous sunlight followed by 42 years of darkness. Only one spacecraft, Voyager 2, has visited Uranus, flying past in 1986.
Neptune, the farthest planet, is only slightly warmer than Uranus at the top of its clouds. It has the fastest winds in the solar system, reaching more than 2,000 kilometers per hour.
Did You Know?
Uranus was the first planet discovered with a telescope. William Herschel spotted it in 1781 and first thought it was a comet.