Monday, May 28, 2007

Solar Radiation Storm

Solar radiation storms are swarms of electrons, protons and heavy ions accelerated to high speed by explosions on the sun. Here on Earth we are protected from these particles by our planet's atmosphere and magnetic field.

Astronauts in Earth orbit are fairly safe, too; Earth's magnetic field extends out far enough to shield them. The danger begins when astronauts leave this protective cocoon. The Moon and Mars, for instance, have no global magnetic fields, and astronauts working on the surface of those worlds could be at risk.

Spacecraft and satellites are also affected. Subatomic particles striking CPUs and other electronics can cause onboard computers to suddenly reboot or issue nonsense commands. If, say, a satellite operator knows that a storm is coming, he can put his craft in a protective "safe mode" until the storm passes.

The type of particle most feared by astronaut safety experts is the ion, that is, an atom which has lost one or more of its charge-balancing electrons. Energetic ions can damage tissue and break strands of DNA, causing health problems ranging from nausea to cataracts to cancer.
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So the goal is to predict when the ions will arrive. The key it turns out, are electrons. Electrons are always detected ahead of the more dangerous ions.

This has been known for years, but only recently has research turned the electrons first aspect of radiation storms into a forecasting tool.

The key to the breakthrough was the COSTEP instrument onboard SOHO. COSTEP is short for "Comprehensive Suprathermal and Energetic Particle Analyzer." Essentially, the device counts particles coming from the sun and measures their energies.

Arik Posner, a physicist in NASA's Science Mission Directorate, looked at hundreds of radiation storms recorded by COSTEP between 1996 and 2002, and was able to construct an empirical, predictive matrix that can be used to forecast the ions' arrival time from the electron data.

Posner's ion storm forecasting matrix.
After testing the results, the matrix was used on COSTEP data gathered in 2003, a year that had not yet been analyzed and 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. The method did, however, also create three false alarms from the 2003 dataset. Improvements will come as Posner works his way through even more of COSTEP's dataset.

The Solar and Heliospheric Observatory (SOHO), is a project of international cooperation between ESA and NASA.
Artist's concept of a radiation storm approaching Earth. Courtesy of Dr. Tony Phillips

Cosmic rays pose a threat to astronauts bound for Mars.
Researchers discuss what a big proton storm might do to someone on the Moon.

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