Launched nearly 5 years ago, the five identical THEMIS spacecraft 
targeted one of heliophysic's most pressing research problems: the
cause of geomagnetic substorms.  Lining up in the Earth's magnetotail
once each 4 days during the first two years of the mission, the spacecraft
provided the observations needed to demonstrate that magnetic 
reconnection releases solar wind energy stored in the Earth's magnetotail,
resulting in brilliant auroral displays, strong field-aligned currents into
the Earth's ionosphere, and injections of energetic particles into the
Van Allen radiation belts.  Two of the spacecraft were then moved to
lunar distance to form the ARTEMIS mission- tasked with determining
the surface and interior magnetic field structure of the Moon, its plasma
and magnetic field environment, and the nature of the lunar wake.  The
other three THEMIS spacecraft remain in near-Earth orbits, where they 
continue to make fundamental discoveries concerning the nature of
storms/substorms, the radiation belts, and magnetopause physics.  
THEMIS and ARTEMIS will provide the outer boundary conditions for
the recently launched Van Allen Probes, and provide context by flying
in formation with the forthcoming MMS mission.


About the speaker:
David Sibeck is the THEMIS/ARTEMIS Project Scientist in the Space Weather Laboratory at NASA Goddard Space Flight Center