The Eight Planets

Eight planets travel around the Sun. The four closest — Mercury, Venus, Earth, and Mars — are small and rocky, with solid ground you could stand on. The four farthest — Jupiter, Saturn, Uranus, and Neptune — are enormous balls of gas and ice called the giant planets, with no solid surface at all.

Mercury is the closest planet to the Sun and the smallest. It has no real atmosphere, so during the day it scorches at over 400°C, but at night it plunges to −180°C. Venus is the hottest of all, wrapped in thick poisonous clouds that trap heat like a blanket. Surprisingly, Venus is hotter than Mercury even though it is farther from the Sun, because of those heat-trapping clouds.

Earth is our home and, as far as we know, the only planet with life. It sits at just the right distance from the Sun for liquid water. Next out is Mars, the 'Red Planet', whose rusty colour comes from iron in its soil. Robots called rovers trundle across Mars right now, searching for signs that water — and maybe even life — once existed there.

Jupiter is the giant of our solar system — more than twice as massive as all the other planets put together. Its famous Great Red Spot is a storm that has been spinning for hundreds of years. Saturn's spectacular rings are made of billions of chunks of ice and rock, ranging from tiny grains to boulders the size of houses.

Uranus and Neptune are the two farthest planets, both a deep blue colour because of a gas called methane in their air. Neptune is the windiest place in the solar system, with storms that howl faster than 2,000 kilometres per hour. They are so far away that sunlight there is dim, and a single trip around the Sun takes Neptune 165 Earth years.