Jan 24, 2001

Earth's Invisible Magnetic Tail





The first global views of our planet's magnetosphere, captured by NASA's IMAGE spacecraft, reveal a curious plasma tail that stretches toward the Sun.


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January 25, 2001 -- The first large-scale pictures of the hidden machinations of the Earth's magnetic force-field are now available, including confirmation of a suspected but previously invisible "tail" of electrified gas.


The tail, which streams from Earth towards the Sun, was spotted by NASA's Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft. It's featured on the cover of the Jan. 26 issue of the journal Science. IMAGE is offering researchers an unprecedented view of the transparent, electrified gas trapped within Earth's magnetic field, providing the first visual, global perspective on magnetic storms.

Right: The Extreme Ultraviolet imager (EUV) instrument on board IMAGE captured this picture of the ultraviolet glow from relatively cold plasma surrounding our planet. A hook-shaped "tail" of plasma, near the top-left, streams toward the Sun. The small, faint circle near the center of the image traces ultraviolet radiation from aurora borealis (or "Northern Lights"). [more]

The region laced by Earth's magnetic field, called the magnetosphere, dominates the behavior of electrically charged particles in space near Earth and shields our planet from the solar wind. Explosive events on the Sun can charge the magnetosphere with energy, generating magnetic storms that occasionally affect satellites, communications and power systems.




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It's difficult for any one spacecraft, or even a small fleet, to obtain a coherent, large-scale view of activity in this vast region because the magnetosphere extends even beyond the Moon on the night side of the Earth.

"Imagine trying to track and understand the formation of hurricanes without the view from weather satellites," said Dr. Thomas Moore, IMAGE Project Scientist at NASA's Goddard Space Flight Center. "Like the first meteorologists with a small number of measuring stations, we had an incomplete and at times misleading view of the magnetosphere before IMAGE, because we couldn't see the big picture."

"IMAGE is providing for the first time global views of the Earth's charged-particle populations at multiple wavelengths and energies on time scales of a few minutes, which is sufficient to track the dynamics of the magnetosphere," said Dr. James Burch, IMAGE Principal Investigator and lead author of the Science paper at Southwest Research Institute.


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Above: The blowing solar wind distorts Earth's magnetic field so that it looks much like a teardrop or an airport wind sock. [more information]

The Earth's magnetosphere traps electrified gas, called plasma. The new IMAGE pictures show a tail-like structure in the Earth's own plasma cloud that forms as some of the gas streams toward the Sun. The structure was predicted 30 years ago, but previous spacecraft were unable to confirm its existence.

The tail structure is believed to be a return flow of plasma that occurs when the solar wind buffets the magnetosphere and distorts its shape. For example, a falling raindrop is at first roughly spherical. As it falls and gains speed, air resistance causes the droplet to change shape as water is dragged from the bottom (head) to the top (tail). Surface tension prevents most of the water from simply dispersing from the tail, so it is forced instead to flow within the raindrop and return to the head.

The solar wind distorts the Earth's magnetosphere in a similar way, compressing it on the Earth's day side, like the head of a raindrop. The region is stretched on the night side, like the raindrop's tail, forming a teardrop shape.


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Plasma near the boundaries of the magnetosphere is dragged with the solar wind, but then is turned around and forced back towards the Sun. Although the Sun-pointing plasma tail was expected, IMAGE uncovered some surprises too. For one thing, the spacecraft discovered areas in Earth's plasma cloud that are nearly empty of plasma. The IMAGE team calls these unexpected structures "troughs" and is trying to discover how they form.


IMAGE, launched March 25, 2000, also revealed some surprising activity during magnetic storms, which occur when the solar wind pummels the Earth's magnetosphere. The night-side region of the magnetosphere, which is stretched out by the solar wind, sometimes snaps back and shoots plasma violently toward Earth. The plasma becomes heated to several hundred million degrees and whirls around Earth in multi-million-amp currents. IMAGE discovered that such plasma occasionally is most dense on the Earth's day side, which was unexpected. Researchers are currently studying the phenomenon.

Above: IMAGE's High Energy Neutral Atom (HENA) instrument captured this false color image of neutral atoms glowing inside the hot plasma surrounding Earth. Orange-white denotes the most dense plasma, while red traces the least dense. The hot plasma in this image is densest on Earth's day side, which was unexpected. [more]


Web Links

TRICK O' THE TAIL: IMAGE SATELLITE SEES EARTH'S INVISIBLE MAGNETIC REALM -- Goddard's online press release about the latest IMAGE results includes plenty of related links.

IMAGE home page -- at the NASA Goddard Space Flight Center

From the Drawing Board to the Stars -- Science@NASA article: Dr. Jim Burch, principal investigator for NASA's IMAGE space weather satellite, describes what its like to first imagine a space mission and then make it happen.

The RADAR Cop in Space -- Science@NASA article: NASA's IMAGE satellite will revolutionize our understanding of Earth's magnetosphere and improve space weather forecasting.

Space Weather Satellite Blasts Off -- Science@NASA article: NASA's IMAGE satellite successfully flies into orbit from Vandenberg AFB.


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