NASA spacecraft reveals new details of Earth`s magnetosphere
Washington: NASA`s Wind spacecraft has provided new information about the changing conditions in the Earth`s magnetosphere, a giant bubble created by its own magnetic fields.
As the magnetosphere plows through space, it sets up a standing bow wave or bow shock, much like that in front of a moving ship. Just in front of this bow wave lies a complex, turbulent system called the foreshock. Conditions in the foreshock change in response to solar particles streaming in from the sun, moving magnetic fields and a host of waves, some fast, some slow, sweeping through the region.
To tease out what happens at that boundary of the magnetosphere and to better understand how radiation and energy from the sun can cross it and move closer to Earth, NASA launches spacecraft into this region to observe the changing conditions.
From 1998 to 2002, NASA`s Wind spacecraft traveled through this foreshock region in front of Earth 17 times, providing new information about the physics there.
Lynn Wilson, who is deputy project scientist for Wind at NASA`s Goddard Space Flight Center in Greenbelt, Md. stumbled on some cool squiggles in the data.
"They turned out to be a special kind of magnetic pulsations called short large amplitude magnetic structures, which we call SLAMS for short," Wilson asserted.
SLAMS are waves with a single, large peak, a little like giant rogue waves that can develop in the deep ocean. By studying the region around the SLAMS and how they propagate, the Wind data showed SLAMS may provide an improved explanation for what accelerates narrow jets of charged particles back out into space, away from Earth.
Tracking how any phenomenon catalyzes the movement of other particles is one of the crucial needs for modeling this region. In this case, understanding just how a wave can help initiate a fast-moving beam might also help explain what causes incredibly powerful rays that travel from other solar systems across interstellar space toward Earth.
The material pervading this area of space - indeed all outer space - is known as plasma. Plasma is much like a gas, but each particle is electrically charged so movement is governed as much by the laws of electromagnetics as it is by the fundamental laws of gravity and motion we more regularly experience on Earth.
Since the 1970s, researchers have known that particles seem to be reflecting off the magnetosphere, creating intense particle jets called field aligned ion beams, but it`s not been clear how. Now, the Wind data helps provide a more detailed snapshot of how they form, as it travels through a slew of SLAMS and the ion beams.
Wilson said that the solar wind constantly moves toward Earth`s bow shock and then reflects off it.
"These structures get excited upstream and they start to grow and steepen, kind of like a water wave. But instead of breaking and tumbling over, they stand up, getting bigger and faster," said Wilson.
He said that the SLAMS attempt to move against the gale of solar wind streaming toward them, but ultimately get pushed back, creating a new messy boundary in front of the magnetosphere.
"And then they effectively create their own new bow shock," Wilson added.
Without the SLAMS, one would expect incoming particles from the solar wind to skip and slide along the outside of the bow shock, the way flowing water in a river might move around a large rock. But the SLAMS create a kind of magnetic mirror, causing the solar particles to reflect, attenuating them into one of these field-aligned ion beams, shooting out along magnetic fields back out and away from Earth.
Wind data does not inherently show which of these things create the other, it simply shows the presence of both. However, the ion beams were not seen in the space between the front of the true bow shock and the SLAMS-only streaming away from the SLAMS out toward space. The beams also only appeared after the SLAMS had a chance to fully form.
This strengthened the conclusion that the SLAMS themselves lead to the beams, acting as a magnetic mirror to reflect the particles outward.
Wilson and his colleagues published a paper on these results in the Journal of Geophysical Research online last month.
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