General Information

Despite being the closest planet to the Sun, Mercury has an average surface temperature of 

-173˚C (-279˚F). The planet has virtually no atmosphere and no natural gases to create an atmosphere. The planet is known as the smallest, densest, has an old surface, largest daily variations in surface temperature and has been explored the least. Like Earth, Mercury has a global magnetic feild. Venus and Mars do not. Less than 50% of the planet has been imaged by a spacecraft. Mercury was named after the messenger of the gods (Hermes in Greek mythology).

Watermelon Mercury.jpg

The Facts and Figures

  • 'Average Distance from t'he Sun: 57,909,175 km (35,983,095 miles) (0.38709893 A.U)
  • Radius: 2,439.7 km (1,516 miles) (0.3825 x Earth)
  • Volume: 0.054 x Earth's
  • Mass: 0.055 x Earth's
  • Density: 5.427 g/cm³ (0.984 x Earth)
  • Surface Area: 0.147 x Earth
  • Gravity: 3.7 m/s² (12.1 ft/s²) (If you weigh 100 lbs. on Earth, you would weigh 38 lbs. on Mercury.)
  • Length of Day: 58.65 Earth days
  • Length of Year: 87.97 Earth days
  • Orbit Velocity: 172,341 km/h (107,088 mph)
  • Surface Temperature: -173/427 ˚C (-279/801 ˚F)

Internal Structure

Mercury is one out of four terrestrial planets our solar system, and is solid like Earth.

  • Geologists estimate that Mercury's core occupies nearly 42% of it's volume (for Earth, this porportion is 17%). Recent research strongly suggests that Mercury has a molten core. It most likely contains a higher iron content than any other major planet in our entire Solar System.
  • Surrounding the core is a 500-700 km mantle consisting silicates.
  • Based on data from the Mariner 10 mission and Earth-based observation, Mercury's crust is etimated to be 100-300 km thick. One of many distinctive feature of Mercury's crust is the presence of numerous narrow ridges, and these ridges can extend up to several hundred kilometers. It is estimated these were formed whie Mercury's core and mantle cooled and contracted at a time when the crust had already solidified. Mercury's core is known to have a higher iron content than that of any other major planet in our Solar System.


The first spacecraft to visit Mercury was NASA's Mariner 10 (1974-1975). A second NASA mission to Mercury, named MESSENGER was launched on August 3, 2004, from the Cape Canaveral Air Force Station aboard the Boeing Delta 2 rocket. To reach Mercury's  orbit, the spacecraft must travel 7.9 billion kilometers (4.8 billion miles). The spacecraft will have circled our Sun 15 times befor it settles into Mercury's orbit.