Mercury is the smallest planet in our solar system. It’s just a little bigger than Earth’s Moon. Mercury itself, though, doesn’t have any moons. It is the closest planet to the Sun, but it’s actually not the hottest. Venus is hotter.
Along with Venus, Earth, and Mars, Mercury is one of the rocky planets. It has a solid surface that is covered with craters. Instead of an atmosphere, Mercury possesses a thin exosphere made up of atoms blasted off the surface by the solar wind and striking meteoroids. Mercury's exosphere is composed mostly of oxygen, sodium, hydrogen, helium, and potassium. Mercury doesn’t have any moons.
This small planet spins around slowly compared to Earth, so one day lasts a long time. It takes 59 Earth days to make one day (or one full rotation) on Mercury. However, a year on Mercury goes by fast! Because it’s the closest planet to the Sun, it doesn’t take very long to go all the way around. It completes one revolution around the Sun in just 88 Earth days. If you lived on Mercury, you’d have a birthday every three months!
A day on Mercury is not like a day here on Earth. For us, the Sun rises and sets each and every day. Because Mercury has a slow spin and short year, it takes a long time for the Sun to rise and set there. Mercury only has one sunrise every 180 Earth days! Isn't that wild?
Structure and Surface
- Mercury is the smallest planet in our solar system.
- Mercury is a terrestrial planet. It is small and rocky.
- Mercury has a thin exosphere.
- Mercury’s surface can be as hot as 800 degrees F during the daytime and as cold as -300 degrees F during the nighttime. (But Mercury is not the hottest planet in the solar system. The hottest planet is Venus.)
- Mercury’s poles have water-ice.
Time on Mercury
- A day on Mercury lasts 59 Earth days.
- A year on Mercury lasts 88 Earth days.
- Mercury does not have any moons.
- Mercury is the closest planet to the Sun.
- Venus is Mercury’s neighboring planet.
- Mercury has been known since ancient times because it can be seen without advanced telescopes.
- Because it is so close to the Sun, Mercury is hard to study from Earth. No people have ever gone to Mercury, but two robotic spacecraft have visited. The spacecraft were called Mariner 10 and MESSENGER.
- MESSENGER mapped Mercury by taking pictures of the planet's surface, including some areas that had not been seen before. It also collected information about what the surface and insides of Mercury are made of.