How Big Is the Planet Mercury?

Mercury, the smallest planet in Earth's solar system, has a circumference of 9,525 miles (15,329 km) — less than the distance between Denver, Colorado, in the US and Pretoria, South Africa. The contrast between the sizes of Earth and Mercury is striking: Mercury's surface area is 28,879,000 square miles (74,797,000 km²), which is less than 15% of Earth's surface area. Its mass is equivalent to 5.5% of the Earth's mass.

More about Mercury:

• Mercury orbits the sun once every 88 days.


• There is no established discovery date for Mercury because it was "known to the ancients," according to the United States' National Aeronautics and Space Administration.


• Although Mercury is the planet closest to the sun, Venus' surface is much hotter. This is because of Venus' thick, dense atmosphere.