Mercury Facts

Mercury Planet Profile

View on Maps: google.com/maps/space/mercury
Moons: None
Distance from Sun:35.98 million mi
Radius: 1,516 mi
Diameter: 4,879 km
Orbital period: 88 days
Mass: 3.285 × 10^23 kg (0.055 M⊕)
Surface Temperature: -173 to 427°C
Number of Moons:None
First Record: 14th century BCE by Assyrian astronomers

The planet Mercury was named by the Romans after their fast-footed messenger god because it circles the Sun faster than any other planet. Mercury was also given other names by various civilizations, each one naming it after their own deity or god.

It’s believed that Mercury has been known to human beings for around 5,000 years. In times gone by, many people thought that some of the planets circled around the Earth. It was a Greek philosopher, Heraclitus that made the case that both Venus and Mercury revolved around the Sun and not the Earth.

Hot and Cold

Mercury is the closest planet to the Sun and is has temperatures that can reach 840 degrees F (450 C). However, due to the fact that Mercury has so little real atmosphere, most of the heat escapes bringing night temperatures to -275 F (-170 C).

These temperature swings of over 1,100 degrees F (600 degrees C) are the largest in our solar system. The lack of any significant atmosphere also makes Mercury unable to ward off the impacts of space objects, making its surface appear pockmarked with all sizes of craters.

Mercury Craters

Around four billion years ago an asteroid about 60 miles wide hit Mercury leaving an impact crater we now call “Caloris Basin” which is nearing 960 mi wide. The impact is compared to 1 trillion 1-megaton bombs and the state of Texas can fit inside the crater. It’s believed that a similar impact may have caused the odd spin that Mercury has.

The surface of Mercury is covered with “lobe-shaped” cliffs that run hundreds of miles and reach up to a mile in height. They were formed during the cooling process that Mercury went through billions of years ago.

What did Spacecraft MESSENGER find?

Even with the intense heat and temperature fluctuations, there are still locations on Mercury that are permanently shaded from the Sun’s heat. In 2012, NASA’s spacecraft MESSENGER found water ice in the craters around the north pole of Mercury.

There may be other areas that have water ice, however, the orbit of MESSENGER didn’t include probing the southern pole. It’s believed that meteorites or comets may be responsible for delivering ice to these locations or water vapor may have been outgassed from the interior of the planet and then out to the poles.

Magnetic Field

There have only ever been two spacecraft that have visited Mercury. Mariner 10 in 1974-1975 took three trips around Mercury, mapping about half of Mercury’s surface. It was Mariner 10 that discovered that Mercury has its own magnetic field.

The magnetic field may only be 1% of that of Earth, but it’s incredibly active, allowing solar wind tornados to appear on Mercury’s surface.  Later the Messenger probe was launched from Cape Canaveral in 2004.

Due to Mercury’s odd elliptical orbit and slow speed of rotation, both sunrise and sunset would appear strange to us. If we watched the sunrise, it would appear to rise, set and then rise up again. The same thing happens during sunset.

Facts about Mercury

  • Mercury is the smallest planet in the solar system.
  • The Earth’s moon is only slightly smaller than the planet Mercury.
  • Your weight on Mercury would be 38% of your weight on Earth.
  • A day on the surface of Mercury lasts 176 Earth days.
  • It takes 88 Earth day to equal one year on Mercury.
  • Even though Mercury is small, it is the second densest planet in the solar system.
  • Mercury’s density is due to its composition, which is mostly heavy rocks and metal.
  • Mercury cooled and heated so many times, it has wrinkles on its surface.
  • Scientists believe that Mercury’s molten core is made of solid iron.

Mercury Quiz

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  • Astronomy for Kids