A Giant Breach in Earth's Magnetic
NASA's five THEMIS spacecraft have discovered a breach in Earth's magnetic field ten times larger than anything previously thought to exist. Solar wind can flow in through the opening to "load up" the magnetosphere for powerful geomagnetic storms. But the breach itself is not the biggest surprise. Researchers are even more amazed at the strange and unexpected way it forms, overturning long-held ideas of space physics.
"At first I didn't believe it," says THEMIS project scientist David Sibeck of the Goddard Space Flight Center. "This finding fundamentally alters our understanding of the solar wind-magnetosphere interaction."
The magnetosphere is a bubble of magnetism that surrounds Earth and protects us from solar wind. Exploring the bubble is a key goal of the THEMIS mission, launched in February 2007. The big discovery came on June 3, 2007, 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 who has been analyzing the data. Li's colleague Jimmy Raeder, also of New Hampshire, says "1027 particles per second were flowing into the magnetosphere—that's a 1 followed by 27 zeros. This kind of influx is an order of magnitude greater than what we thought was possible."
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.
Above: A computer model of solar wind flowing around Earth's magnetic field on June 3, 2007. Background colors represent solar wind density; red is high density, blue is low. Solid black lines trace the outer boundaries of Earth's magnetic field. Note the layer of relatively dense material beneath the tips of the white arrows; that is solar wind entering Earth's magnetic field through the breach. Credit: Jimmy Raeder/UNH
The size of the breach took researchers by surprise. "We've seen things like this before," says Raeder, "but never on such a large scale. The entire day-side of the magnetosphere was open to the solar wind."
The circumstances were even more surprising. Space physicists have long believed that holes in Earth's magnetosphere open only in response to solar magnetic fields that point south. The great breach of June 2007, however, opened in response to a solar magnetic field that pointed north.
"To the lay person, this may sound like a quibble, but to a space physicist, it is almost seismic," says Sibeck. "When I tell my colleagues, most react with skepticism, as if I'm trying to convince them that the sun rises in the west."
Here is why they can't believe their ears: 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. In the language of space physics, a north-pointing solar magnetic field is called a "northern IMF" and it is 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."
Northern IMF events don't actually trigger geomagnetic storms, notes Raeder, but they do set the stage for storms by loading the magnetosphere with plasma. A loaded magnetosphere is primed for auroras, power outages, and other disturbances that can result when, say, a CME (coronal mass ejection) hits.
The years ahead could be especially lively. Raeder explains: "We're entering Solar Cycle 24. For reasons not fully understood, CMEs in even-numbered solar cycles (like 24) tend to hit Earth with a leading edge that is magnetized north. Such a CME should open a breach and load the magnetosphere with plasma just before the storm gets underway. It's the perfect sequence for a really big event."
Sibeck agrees. "This could result in stronger geomagnetic storms than we have seen in many years."
For more information about the THEMIS mission, visit http://nasa.gov/themis
SOURCE: NASA Headlines Dec 16, 2008
|Leaks Found in Earth's Protective
By Andrea Thompson, Senior Writer
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.
|Scientists find hole in Earth's
AP News Service
LOS ANGELES – Recent satellite observations have revealed the largest breach yet seen in the magnetic field that protects Earth from most of the sun's violent blasts, researchers reported Tuesday. The discovery was made last summer by Themis, a fleet of five small NASA satellites.
Scientists have long known that the Earth's magnetic field, which guards against severe space weather, is similar to a drafty old house that sometimes lets in violent eruptions of charged particles from the sun. Such a breach can cause brilliant auroras or disrupt satellite and ground communications.
Observations from Themis show the Earth's magnetic field occasionally develops two cracks, allowing solar wind — a stream of charged particles spewing from the sun at 1 million mph — to penetrate the Earth's upper atmosphere.
Last summer, Themis calculated a layer of solar particles to be at least 4,000 miles thick in the outermost part of the Earth's magnetosphere, the largest tear of the protective shield found so far.
"It was growing rather fast," Themis scientist Marit Oieroset of the University of California, Berkeley told an American Geophysical Union meeting in San Francisco.
Such breaches are temporary, and the one observed last year lasted about an hour, Oieroset said.
Solar flares are a potential danger to astronauts in orbit but generally are not a risk to people on the surface of the Earth.
The research was funded by NASA and the National Science Foundation.
Scientists initially believed the greatest solar breach occured when the Earth's and sun's magnetic fields are pointed in opposite directions. But data from Themis found the opposite to be true. Twenty times more solar wind passed into the Earth's protective shield when the magnetic fields were aligned, Oieroset said.
The Themis results could have bearing on how scientists predict the severity of solar storms and their effects on power grids, airline and military communications and satellite signals.
The Themis satellites were launched to find the source of brief powerful geomagnetic disturbances in the Earth's atmosphere.
SOURCE: Yahoo News
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