For the first time, a satellite has attained an orbital path around the Solar System's innermost planet, Mercury. After three fly-bys, the MESSENGER (MErcury Surface, Space ENvironment GEochemistry and Ranging) spacecraft achieved orbital status around the small planet as NASA and the rest of the world watched via NASA Television. The space agency officially announced on their website that the satellite achieved orbital insertion at 9:10 p.m. EDT Thursday, March 17.
"This mission will continue to revolutionize our understanding of Mercury during the coming year," NASA Administrator Charles Bolden said. He was at MESSENGER mission control at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., when engineers received the telemetry data that confirmed that the spacecraft had indeed achieved an orbital pattern above Mercury. In a statement that seemed to be directed toward politicians currently debated the National Aeronautics and Space Administration, he added, "NASA science is rewriting text books. MESSENGER is a great example of how our scientists are innovating to push the envelope of human knowledge."
NASA hopes the spacecraft will begin transmitting collected data from Mercury on April 4, when the satellite's primary science phase will begin. Before that, the APL (Applied Physics Laboratory), MESSENGER's builder, will run a series of instrument checks to see if the craft is operating well in the small planet's extreme conditions.
Data collection is not guaranteed, however, due to the planet's proximity to the sun. According to National Geographic, at its nearest point, it revolves at a distance of 29 million miles. At its farthest, 43 million. And it moves quickly through space, making a circuit around the sun every 88 days.
The spacecraft will study several areas of interest, including scientific the planet's composition, the structure of its core, the magnetic field, and the materials at the poles.
Sean Solomon, MESSENGER principal investigator of the Carnegie Institution of Washington, said that Mercury was relatively unexplored, despite its proximity to the Earth (approximately 96 million miles). "For the first time in history," he noted, "a scientific observatory is in orbit about our solar system's innermost planet. Mercury's secrets, and the implications they hold for the formation and evolution of Earth-like planets, are about to be revealed."
Peter Bedini, project manager at APL, stated: "Achieving Mercury orbit was by far the biggest milestone since MESSENGER was launched more than six and a half years ago. This accomplishment is the fruit of a tremendous amount of labor on the part of the navigation, guidance-and-control, and mission operations teams, who shepherded the spacecraft through its 4.9-billion-mile journey."
The reason MESSENGER's journey for the 96 million mile trip took nearly 5 billion miles to complete is one of exploratory prudence. A direct shot at an orbital attempt would have most likely caused a failed effort where the satellite would have been captured by the gravitational pull of the sun and continued its journey until it vaporized. The spacecraft's circuitous path to its final destination allowed it to slow and match paths with the small planet. The path taken also allowed the satellite to make three separate fly-bys where it collected data as well. Still, the craft had to fire its thrusters for 15 minutes, thereby slowing its momentum by nearly 2,000 miles per hour in its final approach.
Although MESSENGER is the first satellite to orbit Mercury, it was not the first to visit the planet. That milestone was achieved 37 years earlier by Mariner 10 in March 1974. The craft also made a second fly-by in September 1974 and a third in March 1975.