Planets in Order: Solar System Quiz
Eight planets in order
The eight planets, in order from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A popular way to remember them is the sentence 'My Very Educated Mother Just Served Us Nachos'.
Mercury, the closest, orbits about 58 million kilometers from the Sun. Earth is third, at about 150 million. Neptune, the farthest, is about 30 times farther out than Earth, so far that sunlight takes more than four hours to reach it.
There used to be nine planets. In 2006 astronomers agreed on a stricter definition of a planet, and Pluto, which shares its part of space with many similar icy bodies, became a dwarf planet.
The rocky inner planets
The four planets closest to the Sun, Mercury, Venus, Earth and Mars, are small and made of rock and metal. They have solid surfaces you could stand on, and few moons or none: Earth has one, and Mars has two tiny ones.
Being closer to the Sun doesn't make a planet hotter. Venus is wrapped in thick clouds and a carbon dioxide atmosphere that trap heat, so its surface is over 450 °C, hotter than Mercury's.
Mars looks red because its soil and dust are full of iron oxide, the same compound as rust. Earth, the third planet, is the only one known to have liquid water on its surface, and life.
The giants
Beyond Mars lie the four giant planets. Jupiter and Saturn are gas giants, made mostly of hydrogen and helium; Uranus and Neptune are smaller ice giants, with more water, ammonia and methane. None of them has a solid surface.
Jupiter is the largest by far, more than twice as massive as all the other planets put together. Its Great Red Spot is a storm wider than Earth that has been watched for more than 150 years.
All four giants have rings, but Saturn's are the biggest and brightest, made of countless pieces of ice and rock. Uranus is the odd one out: its axis is tilted about 98 degrees, so it rolls around the Sun on its side.