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![]() ![]() Mercury is the closest planet to the sun, 57,910,000 kilometers from the sun. It rotates around it's axis very slowly, completing three rotations in every two years! It is the eigth largest planet in our solar system, and has a very weak magnetic field, and has no known satellites. The temperature on Mercury varies from 90K to 700K, the most extreme temperature variations of any planet in our solar system. It has a diameter of 4,880 kilometers, and a mass of 3.03e32. Mercury is also known as both the Morning Star and the Evening Star, as it can be seen low on the horizon in early morning and evening. Mercury's orbit is extremely eccentric. At the closest point to the sun, Mercury is only 46 million kilometers away, and at the farthest is about 70 million kilometers away. 19th century astronomers made careful obsevations but could not explain them using the Newton's theories. They believed that another planet, called Vulcan, might exist in an orbit near Mercury's to account for the discrepency. Scientists could not figure it out until Einstein's theory of relativity. Mercury is very similar to the moon in many ways. It is very old, and it's surface has many craters. It has no plate tectonics. However, Mercury is much more dense than the moon, and it has an iron core with a radius from 1800 to 1900 kilometers. The crust is only 500 to 600 kilometers thick. Some of the core is probably molten. Mercury has a very thin atmosphere that is blasted with solar wind. Mercury's atmosphere is therefore unstable, with parts of it being blown off and then replenished by the solar wind. Mercury was named after the Greek messenger god, Mercury (in Roman mythology, known as Hermes). The god Mercury wore winged glass sandals that carried him through the air very quickly, so that he could deliever the messages to the gods quickly. The planet Mercury was probably named after the messenger god because it traves so quickly around the sun. Only one satellite has ever visited Mercury, Mariner 10. It flew by three times in 1974 and 1975. Only about 45% of the surface was mapped, so little is known about the surface features of Mercury. One of the largest known features on Mercury's surface that we know about is the Caloris Basin. It is approxamatley 1300 km in diameter. It was probably caused by a large impact in the early history of the solar system. Merucry also has regions of realtivley smooth plains, but what caused them isn't known (there are theories, but nothing's been proved, and not enough is known). NASA is planning to send another satellite, Messenger in 2004, which will orbit Mercury by the year 2009. ![]() << Back to the Sun || On to Venus >> Basics Home |