09.15.08
WIth just three weeks to go before the MESSENGER spacecraft flies by Mercury for the second time, mission team members are gearing up to continue the investigations that began during their first Mercury encounter last January.
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Volcanoes have been discovered on Mercury's surface from images acquired during MESSENGER's first Mercury flyby, as reported in the July 4, 2008, issue of Science magazine. This image shows the largest feature identified as a volcano in the upper center of the scene. The volcano has a central kidney-shaped depression, which is the vent, and a broad smooth dome surrounding the vent. The volcano is located just inside the rim of the Caloris impact basin. The rim of the basin is marked with hills and mountains, as visible in this image. The role of volcanism in Mercury's history had been previously debated, but MESSENGER's discovery of the first identified volcanoes on Mercury's surface shows that volcanism was active in the distant past on the innermost planet.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington. |
At 4:40 a.m. ET on October 6, the craft will speed by the planet, passing within 125 miles (200 kilometers) and gaining a gravity assist that will tighten its orbit and keep it on its course to pass the planet one last time next year before becoming the first spacecraft ever to orbit Mercury, beginning in 2011.
A comprehensive set of observations of Mercury and its environment has been designed for this upcoming encounter. All seven science payload instruments will be deployed, in addition to the telecommunications system.
Over the last six months, engineers have been building the software commands needed to implement these observations into one single sequence that will be loaded to the spacecraft to run automatically during the encounter. The development of this sequence included several levels of review and testing as it matured. Last week engineers successfully completed the final testing of the commands on the hardware simulator, and on September 29, engineers will send MESSENGER instructions on what observations to perform at each point along the flyby trajectory.
As MESSENGER flew by Mercury on January 14, its instruments imaged 20% of Mercury's surface not previously seen by spacecraft. It took measurements of the planet's magnetic field, exosphere and sodium tail, surface color and composition, and gravitational field. On its second visit, MESSENGER will image an additional 30% of the surface never before seen by spacecraft.
"MESSENGER's first flyby of Mercury produced many surprises," said MESSENGER Principal Investigator Sean Solomon. "The second flyby will bring us close to the opposite side of the planet from the one we visited in January, and the surface we will view at close range for the first time is larger in area than South America. The only safe prediction at this stage of exploring the innermost planet is that we will make new discoveries."
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