A recent fleet of five satellites named THEMIS has caused researchers to rewrite the book on how the Earth's magnetic field interacts with solar radiation.

According to NASA, the latest findings from the THEMIS mission show that Earth's magnetic field, which shields our planet from severe space weather, often develops two holes when the solar wind's magnetic field points North, which allows the largest leaks of solar particles.

NASA's THEMIS mission has overturned a longstanding belief about the interaction between solar particles and Earth's magnetic field.

Earth's magnetosphere works mostly like a bar magnet:

Magnets with opposite polarity attract each other:

Magnets with similar polarity repel each other:

Earth's magnetic field, which shields our planet from particles streaming outward from the Sun, frequently develops two holes(very large holes) that allow the largest leaks, according to researchers sponsored by NASA and the National Science Foundation.

This is Bad News.

Recent observations by the THEMIS spacecraft fleet demonstrate that the previous theory was backwards. "Twenty times more solar particles cross the Earth’s leaky magnetic shield when the sun’s magnetic field is aligned with that of the Earth compared to when the two magnetic fields are oppositely directed," said Marit Oieroset of the University of California, Berkeley, lead author of one of two papers on this research, published May 2008 in Geophysical Research Letters.

Researchers have long suspected that this "closed door" entry mechanism might exist, but didn’t know how important it was. "It's as if people knew there was a crack in a levy, but they did not know how much flooding it caused," said Oieroset.

Previous spacecraft could only sample a small part of this enormous layer of solar particles inside the Earth’s magnetic shield, but the five spacecraft in the THEMIS fleet spanned the entire rapidly-growing layer to give definitive measurements.

While the THEMIS researchers discovered the size of the leak, they didn't know its location(s). This was discovered by Wenhui Li of the University of New Hampshire, Durham, N.H., and his team. They used a computer simulation to discover where two holes frequently develop in Earth's magnetic field, one at high latitude over the Northern hemisphere, and one at high latitude over the Southern hemisphere. The holes form over the daylit side of Earth, on the side of the magnetic shield facing the sun.

The simulation also showed how the leaks develop. As solar particles flow out from the sun, they carry solar magnetic fields past our planet. Li's team realized that the solar magnetic field drapes against Earth's field as it passes by. Even though the two fields point in the same direction at equatorial latitudes, they point in opposite directions at high latitudes, When compression forces the opposite fields together, they link up with each other in a process called magnetic reconnection. This process tears the two holes in Earth's magnetic field and appends the section of the solar field between the two holes to Earth's field, carrying the solar particles on this section into the magnetosphere, according to Li's team. "We've found if the door is closed, the sun tears down a wall. The crack is huge – about four times wider than Earth and more then seven Earth diameters long," said Li, whose paper will be published in an upcoming article of the Journal of Geophysical Research.

Solar particles by themselves don't cause severe space weather, but they get energized when the solar magnetic field becomes oppositely-directed to Earth's and reconnects in a different way. The energized particles then cause magnetic storms that can overload power lines with excess current, causing widespread blackouts. The particles also can cause radiation storms that present hazards to spacecraft in high orbits and astronauts passing through the storms on the way to the moon or other destinations in the solar system. "The more particles, the more severe the storm," said Joachim "Jimmy" Raeder of the University of New Hampshire, a co-author of Li's paper. "If the solar field has been aligned with the Earth's for a while, we now know Earth's field is heavily loaded with solar particles and primed for a strong storm. This discovery gives us a basic predictive capability for the severity of solar storms, similar to a hurricane forecaster's realization that warmer oceans set the stage for more intense hurricanes. In fact, we expect stronger storms in the upcoming solar cycle. The sun's magnetic field changes direction every cycle, and due to its new orientation in the upcoming cycle, we expect the clouds of particles ejected from the sun will have a field which is at first aligned with Earth, then becomes opposite as the cloud passes by."