Mercury: Old Data Reexamined, Future Mission Planned

Mercury is the closest planet to the sun, and it only slightly bigger than Pluto. It is the only planet, besides Earth, to possess a magnetic field, and it also shares a rocky terrain, like the other first four planets in the system. Its surface resembles the Moon with craters, but also contains some smooth plains and a polar region with deposits of possible ice.

It is the only planet that rotates perpendicularly, but a Mercurian day last 58 Earth days as it travels around the sun every 87 Earth days. Mercury has an iron-rich core, which accounts for the fact that it is the densest planet. As part of the Mariner 10 mission in the mid-1970s, NASA received its first close-up images and data of Mercury. The spacecraft had two pass by flights in 1974 and once in 1975, which measured the atmospheric, surface and physical characteristics. On the third and closest encounter, the Mariner 10 past within 327 km of the surface while taking about 300 photographs. Even with the images gained in this mission, only 45 percent of the surface has been mapped.

Because technology has advanced greatly in the past ten years, the data was reexamined a few years ago by two scientists - Mark Robinson and Paul Lucey - using improved image-processing technology and some light reflection discoveries.

The most important discoveries they found were evidence of lava flows on the surface along with deposits from explosive volcanic eruptions. There were also variations of the surface and chemical composition from the other terrestrial planets. Also, they produced a new color image of what Mercury really looks using new light-reflecting technology from Moon-based research.

There are many issue that need further study, including the planet's density, geologic history, structure of core, magnetic field, composition of the polar regions and the gaseous makeup of exosphere.

NASA has designated the exploration of Mercury to be a high priority for many reasons. Scientists believe in-depth study will help us better understand our own planet's formation and the sun's relationship with the planets. To answer these and other questions, NASA is planning the MEercury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission.

The MESSENGER spacecraft will do two flybys before assuming a yearlong orbit to collect data using a set of miniaturized instruments by way of X-rays, lasers, spectrometer, radio waves and images. It will measure the surface, atmosphere and magnetosphere composition.

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