Something unique in our neck of the Milky Way occurred on Thursday evening (March 17): A small American spacecraft that has been buzzing around the solar system since 2004 fired its main engine for about 15 minutes and was captured by the gravitational pull of the inner-most planet, the overheated rock we call Mercury.
In what appeared to be a perfect “orbit insertion burn,” NASA’s Messenger spacecraft becomes Mercury’s first artificial satellite. Messenger will spend the next year examining the scorched planet’s surface, trying to figure out how it was formed and what it might tell us about the formation of the entire solar system.
NASA and mission operators from the Applied Physics Laboratory at Johns Hopkins University are still determining whether Messenger achieved the desired and highly elliptical orbit that will bring the probe to within 124 miles of the surface before looping out as far as 9,300, according to the top-notch Web site, Space.com.
After checking out instruments next week, researchers will begin the first sustained, close-up scientific investigation of Mercury.
Messenger has had a remarkable, nearly 5-billion-mile journey since its launch in August 2004. Despite the fact that mission planners called the Messenger a “flying gas can” when it left Earth, the orbital mechanics of reaching Mercury do not permit a “direct ascent.” Instead, the probe has orbited the sun 15 times in 6.5 years while flying by Earth once and Mercury three times before being properly positioned to orbit the planet. In this case, the sling shot effect really was the most energy efficient way to reach a nearby celestial neighbor.
During the orbit insertion burn, controllers could be heard talking about switching fuel lines on Messenger’s engine to keep the weight of fuel tanks even. That was done to ensure the probe would be precisely aligned to achieve orbit. It took eight minutes for telemetry data to reach mission control, first confirming that the burn had begun, was proceeding nominally and that the engine had shut down on schedule. Operators then cheered when they received early confirmation that Messenger was in Mercury’s gravitational grasp.
Now the fun starts, as researchers begin to peel away Mercury’s mysteries.
At sunset this week, there’s a rare opportunity to view the elusive planet Mercury in the western twilight. Those lucky enough to spot it will see it with new eyes: For the first time, it has a moon called “Messenger.”
Click here to follow the Messenger mission.