Auroras rain down
Magnetic fields shake
Beware the spacequake
Click to launch a computer-simulated movie created by Walt Feimer of Goddard's Scientific Visualization Lab.
A spacequake is a temblor in Earth's magnetic field. It is felt most strongly in Earth orbit, but is not exclusive to space. The effects can reach all the way down to the surface of Earth itself.
"Magnetic reverberations have been detected at ground stations all around the globe, much like seismic detectors measure a large earthquake," says THEMIS principal investigator Vassilis Angelopoulos of UCLA.
It's an apt analogy because "the total energy in a spacequake can rival that of a magnitude 5 or 6 earthquake," according to Evgeny Panov of the Space Research Institute in Austria. Panov is first author of a paper reporting the results in the April 2010 issue of Geophysical Research Letters (GRL).
In 2007, THEMIS discovered the precursors of spacequakes. The action begins in Earth's magnetic tail, which is stretched out like a windsock by the million mph solar wind. Sometimes the tail can become so stretched and tension-filled, it snaps back like an over-torqued rubber band. Solar wind plasma trapped in the tail hurtles toward Earth. On more than one occasion, the five THEMIS spacecraft were in the line of fire when these "plasma jets" swept by. Clearly, the jets were going to hit Earth. But what would happen then? The fleet moved closer to the planet to find out.
"Now we know," says THEMIS project scientist David Sibeck of the Goddard Space Flight Center. "Plasma jets trigger spacequakes."
© Evgeny Panov, Space Research Institute of Austria.During a spacequake, Earth's magnetic field shakes in a way that is analogous to the shaking of the ground during an earthquake.
"We've long suspected that something like this was happening," says Sibeck. "By observing the process in situ, however, THEMIS has discovered something new and surprising."
The surprise is plasma vortices, huge whirls of magnetized gas as wide as Earth itself, spinning on the verge of the quaking magnetic field.
© Science@NASA A THEMIS map of plasma flows during a spacequake. The axes are labeled in Earth radii, so each swirl is about the size of Earth. [larger image]
Acting together, vortices and spacequakes could have a noticeable effect on Earth. The tails of vortices may funnel particles into Earth's atmosphere, sparking auroras and making waves of ionization that disturb radio communications and GPS. By tugging on surface magnetic fields, spacequakes generate currents in the very ground we walk on. Ground current surges can have profound consequences, in extreme cases bringing down power grids over a wide area.
After THEMIS discovered the jets and quakes, Joachim Birn of the Los Alamos National Lab in New Mexico conducted a computer simulation of the rebounding process. Lo and behold, vortices appeared in good accord with THEMIS measurements. Moreover, the simulations suggest that the rebounding process can be seen from Earth's surface in the form of ripples and whirls in auroral displays. Ground stations report just such a phenomenon.
"It's a complicated process, but it all fits together," says Sibeck.
The work isn't finished. "We still have a lot to learn," he adds. "How big can spacequakes become? How many vortices can swirl around Earth at once--and how do they interact with one another?"
Stay tuned for answers from THEMIS.
Vortices swirl
plasma a'twirl
Richter predicts
a magnitude six
EU theory is far ahead of this "discovery".
Perhaps the resources will now address EM effects on and in the earth? Rediscovery of theories set forth over a century may also help!
Plasma scientists to your grant requests ......ready set go!