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.