NASA’s Image Reveals Earth’s Invisible Magnetic Tail

Dolores Beasley
Headquarters, Washington, DC
(Phone: 202/358-1753)

Bill Steigerwald
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-5017)

RELEASE: 01-08

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 and is featured on the cover of the Jan. 26
issue of the journal Science. The new imaging technology offers
unprecedented views of the transparent, electrified gas trapped
within Earth’s magnetic field, providing the first visual,
global perspective on magnetic storms.

The region laced by Earth’s magnetic field, called the
magnetosphere, dominates the behavior of electrically charged
particles in space near Earth and shields the 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.

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 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, Greenbelt, MD. “Like the
first meteorologists with a small number of measuring stations,
we had an incomplete and at times misleading view of the
magnetosphere and magnetic storms 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, San Antonio, TX.

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 (a plasma flow ejected
continuously from the solar surface) buffets the magnetosphere
and distorts its shape. For example, at first a falling raindrop
is 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 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 tail, forming a teardrop shape.

Plasma near the boundaries of the magnetosphere is dragged with
the solar wind, but then is turned around and forced back
towards the Sun, moving around the Earth in tail-like flows.
Although the plasma tails were expected, IMAGE 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, stretching it out on night
side. The night-side region of the magnetosphere suddenly 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 the
hot storm-plasma occasionally is most dense on the Earth’s day
side, which is unexpected. Researchers are currently studying
this.

Images and more information are available at:

http://www.gsfc.nasa.gov/GSFC/SpaceSci/sunearth/imagescience.htm