NASA’s MESSENGER spacecraft will execute the second of three planned Mercury flybys on Monday, as it loops through the inner solar system on a trajectory that will take it into orbit around that planet in 2011.
Mercury has been relatively scantily studied up until now because it is so close to the Sun and it is very difficult to get there. Only one spacecraft, Mariner 10, has flown by it before before — three passes back in 1974 and 1975.
What we know about the planet is that its surface is heavily cratered, with plains formed by volcanic eruptions. It has an extremely thin atmosphere. It is a place of temperature extremes: 840 degrees Fahrenheit during the day, -275 degrees at night. It is only about 43 million miles from the Sun — so from the surface of Mercury, the Sun would appear about two and a half times as large in the sky as it does on Earth. It revolves around the Sun once every 59 Earth days, and rotates on its axis very slowly…once every 176 Earth days. So on Mercury, a day is longer than 2 of Mercury’s years!
The first MESSENGER flyby occurred on January 14. The probe sent back pictures of approximately 20% of the surface that had never been photographed before. Monday’s flyby will have the spacecraft passing just 125 miles above the surface. The overarching goals of the mission are to photograph the planet in its entirety, and to learn more about its composition, structure, and magnetic field.
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http://scitech.blogs.cnn.com/2008/10/03/mercury-flyby-on-tap-for-monday/http://messenger.jhuapl.edu/
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