Nasa Solar Wind Mission encounters 'SLAMS' waves

Earth is surrounded by a giant magnetic bubble called the magnetosphere. 

As it travels through space, a complex system of charged particles from the sun and magnetic structures piles up in front of it. 

Scientists wish to better understand this area in front of the bow shock, known as the foreshock, as it can help explain how energy from the rest of space makes its way past this boundary into the magnetosphere. Nasa Solar Wind Mission.

Credit: NASA/GSFC 

As Earth moves around the sun, it travels surrounded by a giant bubble created by its own magnetic fields, called the magnetosphere.

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.

"I stumbled on some cool squiggles in the data," says Lynn Wilson, who is deputy project scientist for Wind at NASA's Goddard Space Flight Center in Greenbelt, Md.

"They turned out to be a special kind of magnetic pulsations called short large amplitude magnetic structures, (SLAMS)."

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.

Wilson and his colleagues published a paper on these results in the Journal of Geophysical Research online on March 6, 2013.

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.

"One of the unique things about space weather is how little things can have big effects," says David Sibeck, a space scientist at Goddard who is a co-author on the paper.

"An event might seem small and just generate local turbulence, but it can have profound effects downstream.

The front of the magnetosphere is right in the line between sun and Earth, so it's a crucial place to understand which small things can lead to big results."

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.

The scientists' job was to map where these events happen in space and time and to try to determine which events initiate which.

Wilson says that the solar wind constantly moves toward Earth's bow shock and then reflects off it.

"What happens to Earth's magnetic field depends on what's happening here at the front of the bow shock," says Sibeck.

"And what's happening there is dramatic. It's going to affect how much energy moves into the magnetosphere. Once inside the magnetosphere, it can create powerful solar storms and impact communications and GPS satellites that we depend on daily."