According to Astroprof’s Page:
The MESSENGER spacecraft is now nearly to Mercury. It will pass the planet on Monday, January 14, 2008, at about 1:05pm, Central Standard Time.
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MESSENGER (the MErcury Surface, Space Environment, GEochemistry and Ranging spacecraft) is the first space probe to visit Mercury since Mariner 10 last passed that planet in 1975, over three decades ago. Technology and instrumentation have come a long way since then. MESSENGER is far more capable than Mariner 10 ever could have been. Furthermore, MESSENGER aims to do something that Mariner 10 never did: MESSENGER, after several flybys, will enter orbit around Mercury. Mariner 10 only flew past three times. MESSENGER will pass closest to Mercury tomorrow, and then again 266 days later, on October 6, 2008. This is important, because it is about 4.5 Mercury rotations. That means that on the second flyby, MESSENGER will see the opposite side of Mercury lit than the one lit on the first flyby. When Mariner 10 flew past, each time by was almost 3 exact rotations later, so nearly the exact same side of Mercury was lit each time by. As a consequence, half of Mercury could never be seen by Mariner 10. And, not even all of the side lit by the Sun was imaged, so less than half of Mercury has been photographed and mapped. MESSENGER will not have this problem. The MESSENGER website has several animations that show the launch, trip across the solar system, and approach for the spacecraft.
Read more here & here.
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