Illustration of Earth's magnetic field which looks a little like a sideways jellyfish. The jellyfish 'tail' is known as the magnetotail and it flows off to the right in this picture, away from the sun on the 'night side' of Earth.
Credit: Wikimedia
MARYLAND: Special cameras aboard NASA’s Interstellar Boundary Explorer (IBEX) spacecraft have snapped the first shots of the magnetic tail and plasma sheet enclosed within Earth's magnetic field.
Instead of recording light, the IBEX’s two large single-pixel cameras detect energetic neutral atoms. Such fast-moving atoms are formed whenever atoms in the furthest reaches of Earth's atmosphere collide with charged particles and get sent speeding off in a new direction. Called Energetic Neutral Atom or ENA imaging, the technique captured unprecedented images of the plasma.
"Earth’s magnetic tail and its charged particles are invisible to conventional cameras that detect light,” said Jim Slavin, a magnetotail researcher who is the director of the Heliophysics Division at NASA's Goddard Space Flight Centre in Greenbelt, Maryland. "Events going on there have only been inferred based on other kinds of measurements."
Exploring the magnetic jellyfish
Close to the globe, Earth's magnetic field wraps around the planet like a gigantic spherical web, curving in to touch Earth at the poles. But this isn't true as you get further from the planet. As you move to the high altitudes where satellites fly, nothing about that field is so simple.
Instead, the large region enclosed by Earth's magnetic field, known as the magnetosphere, looks like a long, sideways jellyfish with its round bulb facing the sun and a long tail extending away from the sun.
In the centre of that magnetic tail lies the plasma sheet. Here, strange things can happen. Magnetic field lines pull apart and come back together, creating explosions when they release energy. Disconnected bits of the tail called ‘plasmoids’ get ejected into space at two million miles per hour. And legions of charged particles flow back toward Earth.
Such space weather events cause auroras and, when very strong, can produce radiation events that could cause our satellites to fail. But until now no one has been able to take pictures of these fascinating processes in the plasma sheet.
Could be first seen plasmoid formation
"The image alone is remarkable and would have made a great paper in and of itself because it's the first time we’ve imaged these important regions of the magnetosphere," said David McComas, principal investigator of the IBEX mission and assistant vice president of the Space Science and Engineering Division at Southwest Research Institute in San Antonio, Texas. The results appeared online in the Journal of Geophysical Research.
But when they looked closely, the group realised they didn't only have a picture of a quiescent plasma sheet. The various images appear to show a piece of the plasma sheet being bitten off and ejected down the tail. They think they've caught a plasmoid in the moment it was being formed. If they're correct, this would be the first time such an event was directly seen.
