Neptune

Neptune is the eighth and most distant planet from the Sun, a deep-blue ice giant orbiting about 4.5 billion kilometres away. It has the strongest winds in the solar system, reaching over 2,000 kilometres per hour.

Invisible to the naked eye, Neptune was the first planet found through mathematical prediction rather than observation. It takes about 165 Earth years to complete a single orbit of the Sun.

The table above puts that remoteness in numbers. At 30.069 AU Neptune orbits thirty times farther from the Sun than Earth does, so it receives roughly a thousandth of the sunlight we get, and the mean temperature of −201 °C follows directly from that. Its radius of 24,622 km makes it close to four times wider than Earth, yet 17.1 Earth masses spread through that much larger volume give a surface gravity of only 11.15 m/s² — about 14% more than ours, which is a far smaller difference than the size gap suggests.

A Neptunian day is a brisk 16.1 hours, so the winds recorded in its cloud tops are being driven around the planet very quickly indeed. The 165-year orbit is the figure that puts everything else in perspective: Neptune was found in 1846, which means it has completed just one circuit of the Sun since its discovery. Sixteen known moons travel with it. Watch it crawl along the outer edge of the 3D solar system simulator while the inner planets race around the Sun.