NASA SOHO Spacecraft Aids in Forecast of Solar Radiation Storms

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Posted: Friday, May 25, 2007


WASHINGTON - NASA's Solar and Heliospheric Observatory (SOHO) now enables scientists to forecast solar radiation storms, giving future astronauts, traveling to the moon and Mars, time to seek shelter and ground controllers time to safeguard satellites. The new method for the first time offers as much as one hour advance notice when a storm is approaching.

"Solar radiation storms are notoriously difficult to predict. They often take us by surprise, but now we've found a way to anticipate these events," says Arik Posner, a physicist in NASA's Science Mission Directorate, Washington. Posner is on temporary assignment to NASA from Southwest Research Institute, San Antonio. Posner developed the technique. His study appears in a recent issue of the journal Space Weather.

Solar radiation storms are swarms of electrons, protons and heavy ions accelerated to high speed by explosions on the sun. On Earth, humans are protected from these particles by Earth's atmosphere and magnetic field. Astronauts in Earth orbit also are protected since Earth's magnetic field extends far enough to shield them. Solar radiation storms are a potential risk factor for astronauts working on the surface of the moon or Mars since neither has a substantial magnetic field.

"A one hour warning would reduce the odds of being caught in a solar storm outside of a lunar habitat, where astronauts are most vulnerable," says Francis Cucinotta, chief scientist for the NASA Space Radiation Program at NASA's Johnson Space Center, Houston.

Spacecraft and satellites would also benefit. Subatomic particles striking computer processors and other electronics can cause onboard computers to suddenly reboot or issue nonsense commands. If a satellite operator knows that a storm is coming, the craft can be placed in a protective "safe mode" until the storm passes.

The type of particle most feared by safety experts is the ion, an atom that has lost one or more of its charge-balancing electrons. Energetic ions can damage tissue and break strands of DNA, an effect not fully understood in terms of human disease.

The goal of researchers is to forecast when the ions will arrive. "The key is electrons. They are always detected ahead of the more dangerous ions," says Posner. While this has been known for years, only recently has this research turned the "electrons first" aspect of radiation storms into a tool for forecasting.

Every radiation storm is a mix of electrons, protons and heavier ions. The electrons, being lighter and faster than the others, race out ahead. By measuring the "rise time and intensity of the initial electron surge" Posner could predict how many ions were following and when they would arrive.

The key to the breakthrough was the Comprehensive Suprathermal and Energetic Particle Analyzer (COSTEP) instrument on board the observatory. COSTEP counts particles coming from the sun and measures their energies. Posner looked at hundreds of radiation storms recorded by COSTEP between 1996 and 2002, and was able to construct an empirical, predictive matrix that involved plugging an electron data into the matrix, and an ion forecast emerging.

After testing the results, the matrix was used on COSTEP data gathered in 2003, a year not yet analyzed and which formed no part of the matrix itself. The matrix was applied to the electron data and as a result, it successfully predicted all four major ion storms of 2003 with advance warnings ranging from 7 to 74 minutes.

"While the method is not yet perfect, I'd like to improve that," Posner says. Improvements will come as Posner works his way through even more of COSTEP's dataset.

"Launched with SOHO in 1995, COSTEP has been operating through an entire solar cycle including the recent solar maximum in 2001, and it is still going strong," says Prof. Bernd Heber, COSTEP's principle investigator at the University of Kiel, Germany.

The method is being considered by planners at the Johnson Space Center in their design of future lunar missions. "Posner's technique reduces the odds of exposure by more than 20 percent compared to current methods, allowing astronauts to venture farther from their outpost. That's good for both science and exploration," says Cucinotta.

"NASA's Vision for Space Exploration will lead humans away from Earth's protective magnetic cocoon and into the unprotected seas of outer space," says Posner. "New scientific knowledge concerning basic processes of space will ensure safe, effective achievement of NASA's future space exploration activities."

SOHO is a project of international cooperation between the European Space Agency and NASA. For more information on NASA's study of the solar system, visit:

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