Mercury for Kids
Planet 1 from the Sun
Mercury is the first planet from the Sun. Its day lasts 176 Earth days. Its year lasts 88 Earth days. That is from NASA's planetary fact sheet, checked 29 October 2026. A scale there reads 0.378 times as much as on Earth. Read about it at three levels: Little, Middle and Big, and make your own Space Card.
Mercury is the smallest planet, and the closest to the Sun. It is covered in craters, like the Moon. It has no moons of its own.
Mercury zooms round the Sun in just 88 Earth days, but it spins so slowly that one day, from sunrise to sunrise, lasts 176 Earth days. That means a day on Mercury is longer than its year.
With almost no air to hold heat in, Mercury swings from about 430 degrees Celsius in the day to about minus 180 at night. Its surface is crowded with craters from rocks that hit it billions of years ago.
A day on Mercury lasts longer than its year.
Mercury in numbers
| Across | 4,879 km |
|---|---|
| From the Sun | 57.9 million km |
| A day | 176 Earth days |
| A year | 88 Earth days |
| Pull of gravity | 0.378 times Earth's |
| Average temperature | 167 °C |
| Moons | 0 |
Source: NASA planetary fact sheet, checked 29 October 2026.
How big is Mercury?
Mercury is 4,879 kilometers across, 38 out of every 100 parts of Earth's width. Mercury is 58 million kilometers from the Sun, on average.
How hot or cold is Mercury?
Mercury averages 167 degrees Celsius, hotter than boiling water (100 degrees) all the time.
Does Mercury have moons?
Mercury has no moons.
Can I see Mercury tonight?
Not this week: it is too close to the Sun in the sky, lost in its glare. Sky Tonight gives your own times from a ZIP.
How much would I weigh on Mercury?
A child who weighs 80 pounds on Earth would read 30 pounds on Mercury. That is a game number: it only shows how hard Mercury pulls compared with Earth. Make your own Space Card to guess first and see all eleven worlds.