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Cracks Discovered in Earth's Magnetic Shield - 2003-12-03

Scientists have found prolonged weaknesses in Earth's defense against storms on the sun. Our planet's magnetic shield normally deflects most of the effect a solar storm's blast would have on us, but researchers have found lasting cracks in the barrier, that allow charged solar particles to threaten satellites and electrical systems on the ground.

The sun has been very active lately, with storms on its surface spewing tons of hot, electrically-charged particles in our direction. This so-called solar wind interacts with our planet's magnetic field and can induce damaging surges of voltage in electrical systems, like power grids, spacecraft, high frequency radio communications and television.

Space weather forecasters using satellites that measure the particle bombardments have issued several warnings recently so managers of these systems can turn them off to protect their hardware.

The magnetic field extending tens of thousands of kilometers above Earth prevents most of the solar wind from reaching our atmosphere, although some of it slips through to wreak its occasional havoc. The particles pass through cracks in the magnetic field that scientists have known about since the 1960s.

Now, researcher Harald Frey of the University of California at Berkeley and his associates have found that these cracks can persist several hours instead of opening only briefly as previously thought. "It is rather like a drafty old house with the windows stuck open during a heavy rainstorm. The house will still deflect most of the storm, but the couch inside is still ruined," he says.

Mr. Frey's team reports in the journal Nature that it saw what it considered a clue to persistent solar wind leakage into Earth's atmosphere. A U.S. space agency satellite named Image observed an ultraviolet aurora the size of California for several hours in the upper atmosphere above the Arctic. It was generated by solar protons hitting the atmosphere and causing it to glow in light invisible to the human eye.

"So that told us that the process that formed this crack must have been continuously active for many hours. We suspected that the proton spot was created by this process that can break up our magnetic shield in small regions and can allow solar wind particles to flow through this crack," says Mr. Frey.

The researchers' suspicions were confirmed by measurements of a group of four European satellites called Cluster flying directly through the crack.

They found that a bright proton spot in the atmosphere indicating a crack occurs only under certain conditions. Research team member Tai Phan says the Earth's magnetic field and that surrounding the solar wind must connect, with the solar wind's magnetic field pointing north.

"Once we know that a spot is the footprint of the crack in the magnetic shield, we now have a new and powerful tool to detect cracks on a global scale. By looking at proton aura images taken by the Image spacecraft, we can tell where the cracks are and for how long they remain open," he says.

This, in turn, can eventually help us better predict solar wind blasts that might endanger electrical systems, according to University of Michigan researcher Janet Kozyra, who did not take part in the study. "It is critical for us to understand where, when, and for how long the magnetic shield gets breached and how this energy gets in. The more we understand about this, the better we're able to incorporate these processes in global models, and in the future they will help us to make more accurate space weather predictions," she says.

That could mean fewer power outages, lost communications, and disabled spacecraft during a solar eruption.