Mercury, the solar system's smallest planet, has gained a yearlong visitor from Earth - a spacecraft named Messenger that mission controllers guided successfully into a long, looping orbit around the planet Thursday night after a six-year flight across 4.9 billion miles of space.
For the first time, Messenger's polar orbit will enable Earth-bound scientists to see and analyze the planet's entire surface continuously, from distances as close as 124 miles and as far off as 9,420 miles.
Mercury is the planet closest to the sun. It holds an enormous iron core. Its rugged surface has immense craters long bombarded by meteors and comets, and ancient volcanoes that stand above flat, volcanic plains of hardened lava. Its blazing, 800-degree summers and shadowed winters at 270 degrees below zero make observing it from close up a challenging task for the mission's scientists and engineers.
And according to Sean C. Solomon of the Carnegie Institution in Washington, the mission's chief scientist, Messenger's third and final fly-by of the planet in 2009 already has shown a wildly fluctuating and mysterious magnetic field.
"It looked as though we were seeing a complete collapse of the magnetic field," he said. "This is an incredibly dynamic magnetosphere."
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