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July 16, 2007

Cynthia O'Carroll
Goddard Space Flight Center

THEMIS Status - July 16, 2007

Following a spectacular sunset launch on February 17, 2007, the five THEMIS spacecraft were deployed into a 'string-of-pearls' configuration on near-identical highly elliptical orbits with 31-hour periods. The first science observations from the spacecraft were obtained on March 23, during a disturbance in the Earth's magnetic field known as a substorm. The multipoint spacecraft and dedicated ground observatories allowed researchers to track the development of the substorm via a proof-of-concept study demonstrating novel techniques that will be used throughout the course of the mission. All 25 instruments on each spacecraft have been operating well ever since.

During the summer of 2007, the spacecraft are in a "coast phase" collecting information about the interaction of the solar wind and the Earth's magnetic field. At maximum distance from Earth (apogee), the spacecraft lie between the Sun and the Earth. On their way out to and back from apogee each orbit, the spacecraft routinely cross the outer boundary of the Earth's magnetic field and a shock wave that stands upstream from this boundary. Scientists are taking this opportunity to study the outer boundary, known as the magnetopause, and determine how the Sun's plasma and magnetic energy couples into the Earth's environment.

"This first phase of the mission opens a new era in magnetospheric physics, one that allows us to explore the full range of phenomena that occur on the magnetopause." said David Sibeck, project scientist at NASA's Goddard Space Flight Center, Greenbelt, Md.

"These observations will be used to understand how the Earth's magnetic field deflects and shields us from the supersonic solar wind, and how a small fraction of the incident energy penetrates the Earth's magnetic field to power geomagnetic storms, substorms and brilliant auroral displays," added Sibeck.

In September 2007, the five spacecraft will be deployed to their final orbits, with apogees ranging from one sixth to half the distance to the Moon. During the coming Winter seasons of 2007-2008 and 2008-2009, the spacecraft will line up radially once each four days over North America at times suitable for auroral observations, i.e. when the United States lies in darkness near midnight. The combined spacecraft and ground-based observatories will observe and track numerous substorms, offering scientists insight into the mechanisms that generate the ever-changing aurora.


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