Launched in 2007, NASA's five THEMIS spacecraft have now successfully completed their 2 year mission to determine the cause of geomagnetic substorms. Because they are continuing to work perfectly, NASA is re-directing the outermost two spacecraft to special orbits at and around the Moon. This new mission, which is called ARTEMIS, uses some very complex maneuvers over two years (2009-2010) to get both spacecraft into position.
As the Moon orbits the Earth, it passes in and out of the Earth's magnetic field and the million-mile per hour stream of particles emitted by the Sun known as the solar wind. While in these regions, the two ARTEMIS spacecraft will seek evidence for turbulence, particle acceleration, and magnetic reconnection, three fundamental phenomena that control the nature of the solar wind's interaction with the Earth's magnetosphere.
Employing their full complement of instruments and unique two-point vantage points, the spacecraft will study the vacuum the Moon carves out in the solar wind, and the processes that eventually fill this lunar wake. Nearer the Moon, they will observe the effects of surface electric fields, ions sputtered off the lunar surface, and determine the internal structure of the Moon from transient variations in its magnetic field induced by external changes.
After six months at the Lagrange points, ARTEMIS will move in closer to the moon, at first only 100 kilometers from the surface, but eventually even closer. From point-blank range, the spacecraft will look to see what the solar wind does to a rocky world when there is no magnetic field to protect it.
ARTEMIS will work in tandem with current missions, such as NASA's Lunar Reconnaissance Orbiter, LADEE (Lunar Atmosphere and Dust Environment Explorer to launch from Wallops Island, VA) and Grail (Gravity Recovery and Interior Laboratory), and Chang'e 2, a Chinese unmanned probe, to prepare the ground for increased robotic exploration of the moon by future U.S. missions, including the international lunar network.
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