Mercury Fact File


Mercury is the closest planet to the sun and is the second smallest planet in our solar system. It speeds around the sun in a wildly elliptical orbit coming as close as 46 million km and as far as 70 million km from the sun.

It takes Mercury 88 days to complete its trip around the sun moving at nearly 50 km per second (faster than any other planet). Mercury completes three rotations around its own axis for every two orbits around the Sun. One day on Mercury is equivalent to 176 Earth days (or 4224 hours). This means that a "day" on Mercury is equivelent to 2 of Mercury's years - 88 Earth days of sunlight and 88 days of darkness for each actual day.

Due to its proximity to the sun you would expect that Mercury would be the hottest planet in our Solar System, but that honor belongs to Venus. Mercury does however have the largest fluctuation between day and night temperatures. Surface temperatures can reach up to 467 degrees Celsius during the day. At night the temperature can drop as low as -183 degrees Celsius. This is due to the fact that Mercury hardly has an atmosphere that retains heat.

The little atmosphere that exists on Mercury is composed mainly of oxygen, sodium and helium. These atoms quickly escape into space and are constantly replenished by elements blasted from the planet's surface due to solar radiation.

The surface of Mercury is very similar to our moon. It is scarred by thousands of impact craters from collisions with meteorites. These craters are named after famous artists and the largest, Beethoven, is nearly 320 km across. The surface also consists of various inter crater plains, which are believed to have formed either through dust from a meteorite impact (crater ejecta) or through volcanic activity. Winding cliffs called scarps are also visible. These scarps can reach up to 3 km in height and stretch for hundreds of kilometers.

One of the largest and most prominent features on Mercury is the Caloris Basin. It is about 1,300 km in diameter, and is most likely the result of an asteroid that impacted the planet's surface early in it's history.

Mercury: Facts & Figures

  • Average Distance from the Sun : 57,909,175 km
  • Perihelion (closest): Metric: 46,000,000 km
  • Aphelion (farthest): Metric: 69,820,000 km
  • Equatorial Radius: Metric: 2,439.7 km
  • Equatorial Circumference: Metric: 15,329.1 km
  • Mass: 330,220,000,000,000,000,000,000 kg
  • Volume: 60,827,200,000 km3
  • Density: 5.427 g/cm3
  • Surface Area: 74,800,000 km2
  • Equatorial Surface Gravity: 3.7 m/s2
  • Escape Velocity: 15,300 km/h
  • Length of Day: 176 Earth days (4224 hours)
  • Length of Year: 87.97 Earth days
  • Mean Orbit Velocity: Metric: 172,341 km/h
  • Orbital Eccentricity: 0.20563069
  • Orbital Inclination to Ecliptic: 7 degrees
  • Equatorial Inclination to Orbit: 0 degrees
  • Orbital Circumference: 356,000,000 km
  • Minimum/Maximum Surface Temperature: -173/427 C
  • Number of Moons: 0

Source: NASA