Uranus

Uranus is the seventh planet from the Sun, an ice giant with a pale blue-green colour that comes from methane in its atmosphere. It is the coldest planet, with cloud-top temperatures near −220 °C.

Uranus is tipped almost completely on its side, so it appears to roll along its orbit. This extreme tilt gives it decades-long seasons, with each pole spending about 42 years in continuous sunlight and then darkness.

The table above fills in the rest. A radius of 25,362 km makes Uranus close to four times Earth’s width, yet its 14.5 Earth masses are spread so thinly that surface gravity at the cloud tops is 8.87 m/s² — slightly less than ours, so you would weigh a little under 10% less there than at home despite the planet being fourteen times heavier. Orbiting at 19.191 AU, nearly twenty times Earth’s distance from the Sun, it receives well under one per cent of the sunlight we do, and the mean temperature listed is −197 °C.

The 84-year orbit and the roughly 98-degree tilt are what produce those extraordinary seasons: half an orbit is 42 years, so each pole gets 42 years of continuous daylight followed by 42 years of night, while the planet itself turns on its axis every 17.2 hours regardless. Twenty-eight moons are known. Because a single Uranian year is longer than most human lifetimes, the planet barely moves in the 3D solar system simulator even when you run the clock forward.