by Dr. Tony Phillips
July 27, 2010
from ScienceNASA Website
Rumbles without sound
They call it "the spacequake."
A spacequake in action.
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.
Panov is first
author of a paper reporting the results in the April 2010 issue of
Geophysical Research Letters (GRL).
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.
During a spacequake, Earth's magnetic field shakes in a way
that is analogous to the shaking of the ground during an earthquake.
credit: Evgeny Panov, Space Research Institute of Austria.
According to THEMIS, the jets crash into the geomagnetic field some 30,000 km above Earth's equator.
The impact sets off a rebounding process, in which the incoming plasma actually bounces up and down on the reverberating magnetic field. Researchers call it "repetitive flow rebuffing." It's akin to a tennis ball bouncing up and down on a carpeted floor.
The first bounce is a big one, followed by bounces of decreasing amplitude as energy is dissipated in the carpet.
The surprise is plasma vortices, huge whirls of magnetized gas as wide as Earth itself, spinning on the verge of the quaking magnetic field.
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.
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.
Ground stations report just such a phenomenon.
The work isn't finished.