mercury.jpgBack in the early seventies, NASA sent Mariner 10 to Mercury. It was the last in a series of Mariner missions designed to survey other planets in the solar system. Launched in November 1973, this mission provided new information about Mercury and Venus in the Mariner program’s first dual-planet mission. Beginning in March 1974, Mariner 10′s three flybys past Mercury mapped about half of the planet’s surface, during which time a thin atmosphere and a magnetic field were discovered. More than thirty years later, we went back to Mercury this week, for some better pictures…and it was worth the trip.

The NASA spacecraft MESSENGER sent back the first close-up images of Mercury last week, the solar system’s smallest and innermost planet, since the 1973-75 Mariner 10 mission. MESSENGER came as close as 124.6 miles (200.6 kilometers) to the sun-scorched planet on January 14, 2008, during the first of three scheduled flybys before the craft’s expected entry into orbit in 2011. Along the way it captured dozens of images of Mercury’s sunlit side that had been hidden from Mariner 10, the first and until now only craft to visit the planet. This photo, taken from a distance of about 5,800 kilometers (3,600 miles), reveals a long scarp, or cliff, curving from the top left of the image down to the right, interrupted by an impact crater in the top center. The imaged region is around 170 kilometers (100 miles) across.

The MESSENGER science team is in the process of evaluating later images snapped from even closer range showing features on the side of Mercury never seen by Mariner 10. It is already clear that MESSENGER’s superior camera will tell us much that could not be resolved even on the side of Mercury viewed by Mariner’s vidicon camera in the mid-1970s. And they were correct. The spacecraft’s Narrow-Angle Camera on the Mercury Dual Imaging System (MDIS) instrument captured this view of the planet’s rugged, cratered landscape illuminated obliquely by the Sun.

Why Mercury?

There’s still more than half of Mercury we’ve never seen before. And it’s not that NASA hasn’t wanted to get there sooner! Scientists and engineers have spent nearly two decades developing new techniques and designing a spacecraft with the ability to survive the extreme conditions of Mercury. MESSENGER’s science payload (or instrumentation) was selected to answer six key questions about the Solar System’s second densest planet. Most of the instruments are rigidly fixed on the spacecraft’s body, so taking each reading involves maneuvering the spacecraft into the correct position.

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