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An Infinite Guide To Everything Outside Our World

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The Planet Closest to the Sun

The planet Mercury is one of the most difficult planets to study as it is always too close to the sun. Not even the Hubble Space Telescope can study the planet.

Mercury, named after a Roman God, has a very elliptical orbit around the sun. At its closest point, its perihelion, it is about 46 million km (28.6 million miles) from the sun and at its farthest, its aphelion, its about 70 million km (43.5 million miles) from the sun. Mercury is not easily seen from Earth due to its small angular separation from the Sun. Mercury moves around the sun faster than any other planet. Mercury travels about 48 km (30 miles) per second and it takes 88 Earth days to orbit the sun. The Earth goes around the sun once every 365 days (one year).


Mercury is about 77.3 million km (48 million miles) from Earth at its closest approach. The planet rotates once on its axis every 59 Earth days but its interval between one sunrise and the next is about 176 Earth days. Mercury is the second densest major body in the solar system after Planet Earth and its density is slightly less than the Earths. Mercury's smaller mass makes its force of gravity only about a third as strong as that of the Earth. An object that weighs 100 pounds on the Earth would weigh only about 38 pounds on Mercury.

Mercury's Surface

The surface of Mercury consists of cratered terrain and smooth plains and many deep craters similar to those on the moon. The craters formed when meteors or small comets crashed into the planet. The largest known crater is Caloris Basin, with a diameter of 1300 km (800 miles). Like the other terrestrial planets (Venus, Earth and Mars) Mercury is made mostly of rock and metal. Mercury's surface appears to be much like that of the moon. It reflects approximately 6 percent of the sunlight it receives, about the same as the moon's surface reflects. Like the moon, Mercury is covered by a thin layer of minerals called silicates in the form of tiny particles. Scans of Mercury, made by Earth based radar, indicate that craters located at the planet's poles contain water ice. These craters are never in the direct light of the sun so the ice never melts.

What is the temperature on Mercury?

Mercury is the closest planet to the sun but it is not the hottest. This is due to the immense heat escaping through the planet's atmosphere. The temperature on the planet may reach 450 degrees C (840 degrees F) during the day. But at night, the temperature may drop as low as -170 degrees C (-275 degrees F). The sunlight on Mercury's surface is 6.5 times as intense as it is on Earth due its closeness to the sun.

Mercury's atmosphere

Mercury is dry, extremely hot and almost airless. Planet Mercury is too small for its gravity to retain any significant atmosphere over long periods of time. The weak atmosphere contains hydrogen, helium, oxygen, sodium, calcium and potassium. Due to the heat of the planet, the very thin atmosphere is blasted off its surface by the solar wind and quickly escapes into space. Mercury's atmosphere is constantly being replenished. Mercury does not have enough atmosphere to slow down meteoroids and burn them up by friction. The sun's rays are approximately seven times as strong on Mercury as they are on the Earth. The sun also appears about 2 1/2 times as large in Mercury's sky as in the Earth's. The plant and animal life found on Earth cannot survive on Mercury due to the lack of oxygen. Scientists believe that no form of life could live on the planet.

The history of Mercury

Mercury has been known since ancient times. Until the mid-1960's, astronomers believed that Mercury rotated once every 88 Earth days, the same time the planet takes to go around the sun. If Mercury did this, one side of the planet would always face the sun and the other side would always be dark. However, radar studies conducted in 1965 showed that the planet rotates once in about 59 days. The only spacecraft to come close to Mercury was Mariner 10 from 1974 to 1975, which was only able to map 40% to 45% of the planet's surface.

Facts about Mercury

  • The planet is named after the Roman messenger of the Gods

  • It is the second smallest planet at only one third the diameter of the Earth

  • The orbital period of Mercury is 88 days. It takes 58.65 days to rotate on its axis

  • Mercury is very visible from the southern hemisphere and can often be seen in the evening and the morning

  • Mercury looks similar to our moon with its surfave packed with craters and lava flows

  • Caloris basin is the largest crater on Mercury which is 1,300 kilometers in diameter.

  • Mercury has an iron core which creates a magnetic field 1% as strong as the Earths

  • Mercury has no moons

  • Mariner 10 was the only spacecraft to approach the planet in 1974-1975. During its visit it captured 2700 images and covered 45% of the surface

  • There is no possibility of water on the planet as it is too near to the sun. Scientists beleive that ice may be found in some craters that have never faced the sun

  • Flucuations have been found in the temperatures. During the day temperatures can reach 400 degrees c. At night it can fall to -175 degrees c

  • Mercuty's atmosphere contains 42% helium, 42% sodium, 15% oxygen and 1 % other gases

  • From the planet's surface, the Sun will appear two and a half times larger than we see it from Earth. The Earth will appear blue in colour

  • Japan and the European Space Agency are planning a joint venture called Bepicllumbo to map the planet and study its magnetosphere in 2013

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