THEMIS Overview

NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) aims to resolve one of the oldest mysteries in space physics, namely to determine what physical process in near-Earth space initiates the violent eruptions of the aurora that occur during substorms in the Earth's magnetosphere.

THEMIS is a 2-year mission consisting of 5 identical probes that will study the violent colorful eruptions of Auroras.

Understanding and predicting space weather is important to describe the environment in which spacecraft and astronauts operate and ensure their safety. Just as hail and tornadoes accompany the most severe thunderstorms, substorms accompany the most intense space storms – those that disrupt communications, cause power line transmission failures, and produce the most penetrating radiation. THEMIS will study substorms to gain insight into the most severe space storms.

Substorms occur when the magnetosphere suddenly releases vast amounts of stored solar wind energy. Substorms start from a small region in space but within minutes cover an immense region of the magnetosphere. Different possible triggers have different locations, so the key to solving this mystery is placing spacecraft in various locations in Earth's magnetic field to figure to help find the elusive substorm point of origin.

For the first time NASA will launch a constellation of five satellites to study substorms. The THEMIS probes will line up over North America once every four days. Over the mission’s two-year lifetime, the probes should be able to observe some 30 substorms.

THEMIS is the fifth medium-class mission under NASA's Explorer Program, which was conceived to provide frequent flight opportunities for world-class scientific investigations from space within the Heliophysics and Astrophysics science areas. The Explorers Program Office at Goddard Space Flight Center, Greenbelt, Md., manages this NASA-funded mission. The University of California, Berkeley's Space Sciences Laboratory and Swales Aerospace, Beltsville, Md., built the THEMIS probes.