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The Planet Mercury Facts

The name Mercury comes from Roman mythology and refers to the messenger of Jupiter and the god of commerce. In ancient Greece, Mercury was referred to as the morning star (or Apollo) and the evening star (or Hermes). Mercury was initially observed in the third millennia, but most of what we know about the planet was discovered in modern times during the two-year flight of the Mariner 10 spacecraft in the mid-1970s.

Composition
- Mercury is the second smallest planet with a diameter of 3,032 miles. Like the Earth's Moon, Mercury reflects about 6 percent of its received light and is covered with a thin mineral layer of tiny silicate particles. Also similar to the Moon, Mercury is pockmarked and stippled with many craters, steep cliffs and flat plains. The interior of Mercury is similar to that of the Earth, with a rocky mantle under its outer crust and an iron core.
Atmosphere
- Mercury is the closest planet to the sun and orbits from a distance of about 36 million miles. This close proximity makes Mercury extremely hot, dry and airless, because the sun's rays are seven times stronger than the rays on Earth. Mercury's atmosphere is also too thin to reduce the intensity of the sun rays, which results in daytime temperatures of nearly 840 degrees F and night-time temperatures as low as -275 F. Mercury's atmosphere contains hydrogen, helium, oxygen, sodium, calcium and potassium.
Rotation
- Unlike most other planets in the solar system, Mercury has neither moon nor satellite within the well of its gravity. It rotates only once in approximately 59 Earth days, which means that a single day on the planet Mercury would last as long as 176 days on Earth (from one sunset to the next) due to its slow rotation while moving quickly around the sun. The only planet that has a slower rotation than Mercury is the planet Venus.
Viewing and Phases
- Due to Mercury's small size and proximity to the sun, it's difficult to see this planet without the aid of a telescope. It's sometimes possible to spot the planet just after sunset in the west and just before sunset in the east. When Mercury is seen through a telescope, viewers can witness the planet's different phases, which are similar to the phases of the moon because of the shadows the sun casts on its surface.
Scientific Exploration
- Although Mercury was discovered during the earliest days of astronomy, it wasn't possible to get close enough for observation until the Mariner 10 voyage of 1974 and 1975. The "Messenger Spacecraft" was launched on August 3, 2004, with the primary mission to study Mercury and to transmit data to NASA on a regular basis. Messenger's next flyby is scheduled for September 29, 2009, and it should enter orbit around Mercury for long-term study on March 18, 2011.

Astrology