MONDAY, 21 MARCH 2011
The MErcury Surface, Space ENvironment, Geochemistry, and Ranging probe made a flyby of Earth and two flybys of Venus to put it onto the correct trajectory to reach the closest planet to the Sun. Thrusters on the spacecraft slowed MESSENGER down by 1,292 mph to ease it into orbit 96 million miles from Earth .
NASA first visited Mercury with the Mariner 10 probe in 1974, which photographed a landscape of craters, plains and ridges. However, these images didn’t give a good idea of how the planet’s surface was formed. MESSENGER has already mapped some of the remaining parts of the illuminated Mercury hemisphere, but the 12-month orbital phase of the mission will be focused on addressing key questions about the its geologic history and the structure of its core. Scientists are also interested in Mercury's magnetic field, which is dipolar in shape like that of Earth and contrasts with those of Venus, Mars and the Moon. Careful measurements by MESSENGER's magnetometer should help distinguish between the different theories that have been proposed to explain the generation of this magnetosphere .
MESSENGER will also measure the composition of Mercury’s thin exosphere, and its neutron spectrometer will search for hydrogen in the permanently shadowed interior of craters at the planet’s poles. Radar pictures from Earth show material in the craters that resemble ice, but whether these deposits contain water, sulfur or another material is one of Mercury’s great mysteries .
Written by Robert Jones