Three years and four months after launch, NASA’s Messenger probe swept past Mercury for the first time Monday — and was just as quickly on its way again.

Technicians at the Johns Hopkins University’s Applied Physics Lab burst into applause after re-acquiring Messenger’s telemetry, signaling that the spacecraft had successfully navigated its passage of the innermost planet. The flyby is the first of three on Messenger’s unusual cruise. Messenger will return October 6th and again in September of next year before finally settling into orbit around Mercury in 2011.

Scientists are eager to see the data captured by this week’s rendezvous. Despite Mercury’s relative proximity to Earth, Messenger is the first carft to pay a visit since 1975. Mariner 10 managed to image about 55 percent of Mercury’s surface during its mission — pictures which raised almost as many questions as they answered.

The discovery of dramatic surface faulting and other geological surprises led to speculation about whether Mercury may be in a state of planetary collapse. Mariner also noted the presence of a weak magnetic field, a big shock to scientists who thought the planet lacked the molten core supposed necessary for the generation of such a field.

Messenger is carrying a battery of instruments designed to explore these questions, including a sensitive boom-mounted magnetometer. The craft’s electronics and cameras are hidden behind an ceramic fabric shield designed to protect Messenger from the Sun’s intense heat and radiation. Close to Mercury, the Sun’s ray’s are nearly eleven times brighter than on Earth, and direct temperatures can exceed 800 degrees Fahrenheit.

Pre-flyby images show Mercury as an increasingly detailed crescent as Messenger drew closer to its destination. If all goes well, the probe should begin offloading a wealth of his resolution photographs and observational data late Tuesday.

Link: USA Today and NASA’s Messenger Mission Page