NASA's Time History of Events and Macroscale Interaction during Substorms (THEMIS) spacecraft combined with computer models have helped track the origin of the energetic particles in Earth's magnetic atmosphere that appear during a kind of space weather called a substorm. Understanding the source of such particles and how they are shuttled through Earth's atmosphere is crucial to better understanding the Sun's complex space weather system and thus protect satellites or even humans in space.The results show that these speedy electrons gain extra energy from changing magnetic fields far from the origin of the substorm that causes them. THEMIS, which consists of five orbiting satellites, helped provide these insights when three of the spacecraft traveled through a large substorm on February 15, 2008. This allowed scientists to track changes in particle energy over a large distance. The observations were consistent with numerical models showing an increase in energy due to changing magnetic fields, a process known as betatron acceleration.
"The origin of fast electrons in substorms has been a puzzle," says Maha Ashour-Abdalla, the lead author of a Nature Physics paper that appeared online on January 30, 2011 on the subject and a physicist at the University of California, Los Angeles. "It hasn't been clear until now if they got their burst of speed in the middle of the storm, or from some place further away."
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