Orbital fleet dispatched to unravel magnetic storms’ roots

Abstract

To improve scientists’ understanding of geomagnetic storms in Earth's magnetosphere, which can be highly disruptive to a variety of technologies and a health risk to astronauts, five satellites are shifting into orbits as far as halfway to the Moon following the successful 17 February launch of a Delta 2 rocket from Cape Canaveral Air Force Station in Florida. The quintet is at the core of NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, and is designed to detect changes in Earth's space environment including charged-particle accelerations and enhanced plasma waves, all of which occur when the Sun's corona is blasted toward Earth in both the steady stream of the solar wind and during solar storms. The enhanced particle fluxes often cause the planet's magnetosphere to become overloaded with energy, stretching the magnetic field lines in the Earth's magnetotail like rubber bands until they snap back, flinging electrically charged particles toward Earth. The particles travel along the magnetic field lines into the upper atmosphere over the polar regions, where they smash into atoms and molecules, causing them to glow and blanket the skies with shimmering aurorae. Previous studies have been unable to determine where in the magnetosphere the energy of the solar wind transforms into explosive auroras, which, though beautiful, can short-circuit power grids, disrupt GPS satellites and other spacecraft in low-Earth orbit, and bathe astronauts living in space with ionizing particle radiation. Scientists want to know where magnetic disturbances arise in hopes of being able to better predict when they will strike. “For over 30 years, the source location of these explosive energy releases has been sought after with great fervor. It is a question almost as old as space physics itself,” said Vassilis Angelopoulos, the principal investigator for THEMIS and a scientist with the University of California's Space Sciences Laboratory in Berkeley, Calif. “Substorm processes are fundamental to our understanding of space weather and how it affects satellites and humans in geospace,” added Angelopoulos. The purpose of THEMIS is to identify the trigger locations and unravel the physics of the storms’ progressions. “It is not clear exactly what finally snaps in the overloaded magnetosphere to trigger a substorm,” said THEMIS project scientist David Sibeck, with the NASA Goddard Space Flight Center in Greenbelt, Md. “The worst space storms, the ones that knock out spacecraft and endanger astronauts, could be just a series of substorms, one after the other. Substorms could be the building blocks of severe space storms.” The spacecraft will be positioned in orbits ranging from 50,000 miles, or about one sixth the distance to the Moon, to about 150,000 miles above Earth. Once every 4 days the quintet will align over the United States and, together with a network of about 20 ground-based observatories, be in position to make simultaneous observations of the magnetic field over Earth's Northern Hemisphere. Over the network's 2-year lifetime, scientists hope to chart about 30 storms. Observations are expected to begin in December 2008. Irene Klotz is a freelance writer for the American Geophysical Union.