Mercury Facts

  • Mercury has been known to humanity since ancient times (approximately 3,000 B.C.)
  • Early civilizations believed Mercury was actually two different stars--one that appeared in the morning and one that appeared in the evening.
  • Mercury is named after the messenger of the Roman gods.
  • It wasn't until Copernicus put forth his Sun-centered model of the Solar System in the 1500s that is was realized Mercury is a planet.
  • Mercury has no moons or rings.
  • It was once believed that a planet called Vulcan existed between the orbit of Mercury and the Sun.
  • It takes Mercury just under 88 (Earth) days to orbit the sun.
  • Mercury orbits the sun in an ellipse, not a circle. In fact, it's orbit is the least like a circle of all the planets and scientists say it has the most "eccentric orbit" in the Solar System.
  • The temperature on Mercury ranges from -170C (-280F) during the night to 430C (800F) during the day. This is the most extreme temperature change of all the planets.
  • Mercury's axis has the smallest tilt of any of the planets in the Solar System, meaning that there are no seasons on its surface.
  • Mercury rotates three times during two orbits of the sun. It is the only planet that doesn't rotate exactly once every year.
  • The orbit of Mercury was important in proving Albert Einstein's theory of General Relativity.
  • Mercury is the second densest planet in the Solar System. Only Earth has a higher density.
  • Mercury has a large iron core in its center whose radius is 1800 to 1900 kilometers (1100 to 1180 miles).
  • Scientists believe the core of Mercury is probably molten.
  • The outer shell of Mercury is only 500 to 600 kilometers (310 to 375 miles) thick. Earth's outer shell (the mantle and crust) is 2930 kilometers (1819 miles) thick.
  • Mercury has a very thin atmosphere, which is made up of atoms from the surface of the planet that have been blown away by solar winds. As Mercury is so hot, these atoms quickly escape into space and so its atmosphere is constantly being replenished.
  • Mercury has a weak magnetic field whose strength is about 1% of the magnetic field on Earth.