Huge Breach in Earth's Magnetic Field – four times wider than Earth itself

NASA’s five THEMIS spacecraft have discovered a breach in Earth’s magnetic field ten times larger than anything previously thought to exist. 16 Dec 08 – Solar wind can flow in through the opening to “load up” the magnetosphere for powerful geomagnetic storms.

One of the THEMIS probes exploring the space around Earth, an artist's concept.

Researchers are amazed.

This finding fundamentally alters our understanding of the solar wind-magnetosphere interaction,” says THEMIS project scientist David Sibeck of the Goddard Space Flight Center. The magnetosphere is a bubble of magnetism that surrounds Earth and protects us from solar wind.

The big discovery came when the five probes serendipitously flew through the breach just as it was opening. Onboard sensors recorded a torrent of solar wind particles streaming into the magnetosphere, signaling an event of unexpected size and importance.

“The opening was huge—four times wider than Earth itself,” says Wenhui Li, a space physicist at the University of New Hampshire.

The event began with little warning when a gentle gust of solar wind delivered a bundle of magnetic fields from the Sun to Earth. Like an octopus wrapping its tentacles around a big clam, solar magnetic fields draped themselves around the magnetosphere and cracked it open. The cracking was accomplished by means of a process called “magnetic reconnection.”

High above Earth’s poles, solar and terrestrial magnetic fields linked up (reconnected) to form conduits for solar wind. Conduits over the Arctic and Antarctic quickly expanded; within minutes they overlapped over Earth’s equator to create the biggest magnetic breach ever recorded by Earth-orbiting spacecraft, leaving the entire day-side of the magnetosphere open to the solar wind.

The circumstances turned present beliefs upside down. Space physicists have long believed that holes in Earth’s magnetosphere open only in response to solar magnetic fields that point south. This giant breach, however, opened in response to a solar magnetic field that pointed north.

What we once thought should be … isn’t.

The solar wind presses against Earth’s magnetosphere almost directly above the equator where our planet’s magnetic field points north. Suppose a bundle of solar magnetism comes along, and it points north, too. The two fields “should” reinforce one another, strengthening Earth’s magnetic defenses and slamming the door shut on the solar wind. A north-pointing solar magnetic field “should” be synonymous with shields up!

“So, you can imagine our surprise when a northern IMF came along and shields went down instead,” says Sibeck. “This completely overturns our understanding of things.”

The years ahead could be especially lively. For some reason, coronal mass ejections (CMEs) in even-numbered solar cycles (like Solar Cycle 24, which we are now entering) tend to hit Earth with a leading edge that is magnetized north. Such a CME could open a breach and load the magnetosphere with plasma, leaving the earth primed for auroras, power outages, and other disturbances.

“This could result in stronger geomagnetic storms than we have seen in many years,” says Sibeck.

See entire article by Dr. Tony Phillips | Credit: Science@NASA

Thanks to W.G. Campbell for this link

View video version of this story

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THEMIS, short for Time History of Events and Macroscale Interactions during Substorms, is the fifth medium-class mission under NASA’s Explorer Program. The program, managed by The Explorers Program Office at Goddard Space Flight Center, Greenbelt, Md., provides frequent flight opportunities for world-class space investigations in Heliophysics and Astrophysics. The University of California, Berkeley’s Space Sciences Laboratory managed the project development and is currently operating the THEMIS mission. Swales Aerospace, Beltsville, Md., built the THEMIS satellites.


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