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Durable Spacecraft Marks 10 Years Exploring Processes That Create the Aurora
After more than 10 years and 40,000 orbits, a resilient NASA satellite continues to unveil the mysteries of the Earth’s aurora borealis and australis, also known as the northern and southern lights.

An artist's concept of the FAST satellite superimposed on a photo of the aurora taken from the space shuttle. Image to right: An artist's concept of the FAST satellite superimposed on a photo of the aurora taken from the space shuttle. Credit: NASA

The Fast Auroral SnapshoT (FAST) satellite was launched from Vandenberg Air Force Base in California, on August 21, 1996, into a near polar orbit. "In many aspects, the FAST mission has revolutionized our view of the aurora," said Dr. Charles W. Carlson, FAST Principal Investigator, University of California, Berkeley.

The energy source that creates the aurora originates from the solar wind, an electrically charged gas (plasma) released by the sun that impacts the Earth's magnetic field. This energy ultimately sets up electric fields in space that accelerate electrically charged particles trapped in the Earth's magnetic field. The particles slam into the upper atmosphere above the polar regions, generating the dynamic and beautiful glow we know as the aurora.

The solar wind can do more than put on a pretty light show. The brightest aurora are a manifestation of solar storms that disrupt satellites, radio communication, and power plants. Understanding the aurora and other effects of solar storms will help people mitigate these disruptions.

Important discoveries by the FAST team include identification of an "invisible" aurora, not detectable with previous instrumentation, in the form of upward-moving electron beams. These beams explain how the auroral electrical current "returns" to space. This invisible aurora is not detectable on the ground, and systematic detection by FAST established it as a fundamental feature of the aurora. FAST also detected electron solitary waves within these upward-moving electron beams, a discovery that motivated an intense theoretical effort to explain this new phenomena. Solitary waves are low-density bubbles in the charged gas that form due to intense instabilities caused by the beams.

The FAST team was able to solve a long-standing problem of what produces the intense radio emissions from Earth known as Auroral Kilometric Radiation. These are the most powerful naturally-occurring radio waves beamed into space by our planet. Since similar radiation is observed from Jupiter, this discovery also provides the observational evidence to understand Jupiter’s aurora.

A third achievement of the FAST team was the discovery of a new type of aurora powered by intense plasma waves. These waves occur at the most poleward boundaries of the auroral regions and produce some of the most intense auroral displays. This wave-powered aurora also produces the most intense outflows of positively charged atoms (mostly hydrogen and oxygen), and the highest flows of counter-streaming electrons observed near the Earth.

The spacecraft was designed, built, and tested at NASA's Goddard Space Flight Center in Greenbelt, Md. Instruments were provided by the University of California, Berkeley, with contributions from the University of California, Los Angeles, the University of New Hampshire, and Lockheed Martin, Palo Alto, California. "FAST was designed for a one-year lifetime," said Dr. Robert Pfaff, FAST Project Scientist at NASA Goddard. "Because of anticipated radiation damage, the satellite was not expected to last more than a few years. FAST’s longevity is a credit to the scientists and engineers who built the satellite, and to the operations team that has kept the satellite running."

The FAST satellite has collected over five terabytes of data. Its observations have demonstrated the ubiquitous role of particle acceleration by parallel electric fields in nature, with important consequences for planetary, solar, astrophysical bodies. "Due to its scientific productivity and key role in NASA’s current "Great Observatory" program of satellite platforms in the solar system, NASA has recently extended the operations of the FAST mission to 2008," said Pfaff. FAST is funded by NASA Headquarters and is administered by the Explorer Satellite program at Goddard.

Bill Steigerwald
Goddard Space Flight Center