Popular Astronomy

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Image: NASA





Amazing fact!


Mercury rotates very slowly, so its ‘day’ is 59 Earth days long! Yet Mercury’s ‘year’ (the time it takes to rotate around the Sun) is only 88 Earth days long. For every two Mercury years, it has only three days!

     The closest planet to the Sun is little Mercury. It is a rocky planet, grey and covered in craters. In fact, it looks a little bit like the Moon.
      Mercury is the smallest proper planet in the Solar System, at just 3,476 kilometres wide. Some scientists think that it used to be larger, once upon a time, but that it had a collision with another small planet. The collision destroyed the other planet and ripped off Mercury’s outer layers. This would have taken place over four billion years ago.
      If you like sunbathing, Mercury is the place to be. Because Mercury is so close to the Sun, the side facing the Sun can get very hot, up to 430 degrees Celsius. However, the side facing away from the Sun gets very cold, as low as –180 degrees Celsius. Brrr!
      NASA’s Mercury MESSENGER spacecraft is currently orbiting Mercury and has taken some amazing close-up photographs of its surface, like the pictures shown on this page. You can find others here http://messenger.jhuapl.edu/index.php.

Mercury is covered in loads of impact craters, just like our Moon. In the left hand image you can see a large crater in the bottom left that has suffered other impact events on top of it. You may also be able to see a ridge running through the largest crater and one of the craters inside that. The bright, white material in the top of the image is material that has been thrown across the surface in a really big impact event. The right hand image shows a double ring crater, and, if you look closely, you should be able to see chains of smaller craters spreading out from the main crater, which were formed when rocks were thrown out of the crater. Images: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.