The solar wind pushes Earth's protective magnetosphere away from the sun, forming a magnetotail. At full moon, the moon passes through this tail.
Scientists have found two large leaks in Earth?s magnetosphere, the region around our planet that shields us from severe solar storms.
The leaks are defying many of scientists' previous ideas on how the interaction between Earth's magnetosphere and solar wind occurs: The leaks are in an unexpected location, let in solar particles in faster than expected and the whole interaction works in a manner that is completely the opposite of what scientists had thought.
The findings have implications for how solar storms affect the our planet. Serious storms, which involved charged particles spewing from the sun, can disable satellites and even disrupt power grids on Earth.
The new observations "overturn the way that we understand how the sun's magnetic field interacts with the Earth's magnetic field," said David Sibeck of NASA's Goddard Space Flight Center in Greenbelt, Md., during a press conference today at the annual meeting of the American Geophysical Union in San Francisco.
The bottom line: When the next peak of solar activity comes, in about 4 years, electrical systems on Earth and satellites in space may be more vulnerable.
How it works
Earth's magnetic field carves out a cavity in the sun's onrushing field. The Earth's magnetosphere is thus "buffeted like a wind sock in gale force winds, fluttering back and forth in the" solar wind, Sibeck explained.
Both the sun's magnetic field and the Earth's magnetic field can be oriented northward or southward (Earth's magnetic field is often described as a giant bar magnet in space). The sun's magnetic field shifts its orientation frequently, sometimes becoming aligned with the Earth, sometime becoming anti-aligned.
Scientists had thought that more solar particles entered Earth's magnetosphere when the sun's field was oriented southward (anti-aligned to the Earth's), but the opposite turned out to be the case, the new research shows.
The work was sponsored by NASA and the National Science Foundation and based on observations by NASA's THEMIS (Time History of Events and Macroscale Interactions during Substorms) satellite.
How many and where
Essentially, the Earth's magnetic shield is at its strongest when scientists had thought it would be at its weakest.
When the fields aren't aligned, "the shield is up and very few particles come in," said physicist Jimmy Raeder of the University of New Hampshire in Durham.
Conversely, when the fields are aligned, it creates "a huge breach, and there's lots and lots of particles coming in," Raeder added, at the news conference.
As it orbited Earth, THEMIS's five spacecraft were able to estimate the thickness of the band of solar particles coming when the fields were aligned ? it turned out to be about 20 times the number that got in when the fields were anti-aligned.
THEMIS was able to make these measurements as it moved through the band, with two spacecraft on different borders of the band; the band turned out to be one Earth radius thick, or about 4,000 miles (6,437 kilometers). Measurements of the thickness taken later showed that the band was also rapidly growing.
"So this really changes our understanding of solar wind-magnetosphere coupling," said physicist Marit Oieroset of the University of California, Berkeley, also at the press conference.
And while the interaction of anti-aligned particles occurs at Earth's equator, those of aligned particles occur at higher latitudes both north and south of the equator. The interaction is "appending blobs of plasma onto the Earth's magnetic field," which is an easy way to get the solar particles in, said Sibeck, a THEMIS project scientist.
Next solar cycle
This finding not only has implications for scientists' understanding of the interaction between the sun and Earth's magnetosphere, but for predicting the effects to Earth during the next peak in the solar cycle.
The Sun operates on an 11-year cycle, alternating between active and quiet periods. We are currently in a quiet period, with few sunspots on the sun's surface and fewer solar flares, though the next cycle of activity has begun. It is expected to peak around 2012, bringing lots of sunspots, flares and coronal mass ejections (CMEs). CMEs can interact with the Earth's magnetosphere, causing problems for satellites, communications, and power grids.
This upcoming active period now looks like it will be more intense than the previous one, which peaked around 2006, some scientists think. The reason is the changes in the sun's alignment.
During the last peak, solar fields hitting the Earth were first anti-aligned then aligned. Anti-aligned fields can energize particles, but in this case, the energy came before the particles themselves, which doesn't create much of a fuss in terms of geomagnetic storms and disruptions.
But the next cycle will see aligned, then anti-aligned fields, in theory amplifying the effects of the storms as they hit.
Raeder likens the difference to igniting a gas stove one of two ways: In the first way, the gas is turned on and the stove is lit and you get a flame. In the other way, you let the gas run for awhile, so that when you add the gas you get a much bigger boom.
"It should be that we're in for a tough time in the next 11 years," Sibeck said.
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