They went to investigate solar wind-stirred storms in our planet's magnetic field, but, after working for three years, two NASA solar-powered probes faced a dark demise, trapped in the Earth's shadow. NASA researchers now think they can give the twin satellites another shot by altering their courses and sending them instead to study the moon. NASA launched the probes in 2007 as a set of five identical satellites in the THEMIS Mission (Time History of Events and Macroscale Interactions during Substorms), meant to orbit Earth and send information during brief (2-3 hour) "substorms" when the magnetic field surrounding the Earth releases stored energy from solar winds. To understand the start of these "space tornadoes" responsible for the northern and southern lights, NASA placed the probes in very precise orbits, but for two craft that meant, one day, they would face prolonged battery-draining time in the Earth's shadow.
"When we realized that the satellites would be going into very deep shadows, we started thinking of different methods for saving them--even before they were launched," lead scientist Vassilis Angelopoulos, at the University of California, Berkeley, told Discovery News. "We realized that if we had enough fuel to change their orbits, the moon's gravity would start pulling them up."[Discovery News]
As Discovery Newsreports, funding is still pending for the new mission called ARTEMIS (Acceleration Reconnection and Turbulence and Electrodynamics of the Moon's Interaction with the Sun), but the two satellites are already moonward bound. By firing their thrusters to extend their orbits, scientists started moving them closer to the moon in September of 2009, New Scientistreports. If the mission gets final approval, the recycled probes will move into position 62 miles in front of and behind the moon (relative to the Sun), and will give researchers a look at how the moon's magnetic fields interact with solar winds.
The gravitational slingshot effect from these lunar encounters, as well as the probes' close passes near Earth, changed their trajectories drastically – you can see the technical details [and artist renderings] here (pdf). Their own thrusters should be able to do the rest of the job, putting them in orbit around the moon in 2011. . . Not bad for two spacecraft that would have been space junk by now without this creative rescue plan.[New Scientist]
Related content: 80beats: “Space Tornadoes” Power the Northern Lights 80beats: Distant Turbulence in the Magnetic Field Triggers the Northern Lights DISCOVER: Seeing the Light takes readers to an aurora research station in the Alaskan interior DISCOVER: Space Weather explains the damage that solar storms can wreak
Image: Artist's concept of original THEMIS in orbit. / NASA