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Mercury: Overview
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Black and white image of Mercury.
MESSENGER spacecraft images have revealed portions of Mercury never seen by human eyes. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Sun-scorched Mercury is only slightly larger than Earth's moon. Like the moon, Mercury has very little atmosphere to stop impacts and it is covered with craters. Mercury's dayside is super-heated by the sun, but at night temperatures drop hundreds of degrees below freezing. Ice may even exist in craters. Mercury's egg-shaped orbit takes it around the sun every 88 days.

10 Need-to-Know Things About Mercury:

  1. Mercury is the smallest planet in our solar system -- only slightly larger than the Earth's moon.
  2. It is the closest planet to the sun at a distance of about 58 million km (36 million miles) or 0.39 AU.
  3. One day on Mercury (the time it takes for Mercury to rotate or spin once) takes 59 Earth days. Mercury makes a complete orbit around the sun (a year in Mercury time) in just 88 Earth days.
    Color illustration of spacecraft orbiting Mercury.
    MESSENGER: First to orbit Mercury. Image Credit: Johns Hopkins University Applied Physics Laboratory
  4. Mercury is a rocky planet, also known as a terrestrial planet. Mercury has a solid, cratered surface, much like Earth's moon.
  5. Mercury's thin atmosphere, or exosphere, is composed mostly of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K). Atoms that are blasted off the surface by the solar wind and micrometeoroid impacts create Mercury's exosphere.
  6. Mercury has no moons.
  7. There are no rings around Mercury.
  8. Only two spacecraft have visited this rocky planet: Mariner 10 in 1974-5 and MESSENGER, which flew past Mercury three times before going into orbit around Mercury in 2011.
  9. No evidence for life has been found on Mercury. Daytime temperatures can reach 800 degrees Fahrenheit (430 degrees Celsius) and drop to -290 degrees Fahrenheit (-180 degrees Celsius) at night. It is unlikely life (as we know it) could survive on this planet.
  10. Standing on Mercury's surface at its closest point to the sun, the sun would appear more than three times larger than it does on Earth.

Read More About Mercury Blue arrow

Homework? We can help. Link to Mercury homework helper.
Just the Facts
Metric | English | Scientific Notation
Orbit Size (semi-major axis):  5.7909227 x 107 km
Mean Radius:  2.4397 x 103 km
Volume:  6.08272 x 1010 km3
Mass:  3.3010 x 1023 kg
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Last Updated: 21 Jan 2015