Immense cracks in Earth’s magnetic field remain open for
hours, allowing the solar wind to gush through and power
stormy space weather, according to new observations from
NASA’s IMAGE spacecraft and the joint European Space
Agency (ESA) Cluster satellites.

The cracks were previously detected, but researchers now know
they can remain open for long periods, rather than opening and
closing for just very brief intervals. This new discovery
about how the Earth’s magnetic shield is breached is expected
to help space physicists give better estimates of the effects
of severe space weather.

“We discovered that our magnetic shield is drafty, like a
house with a window stuck open during a storm,” said Dr.
Harald Frey of the University of California (UC), Berkeley,
lead author of a paper on this research published Dec. 4 in
Nature. “The house deflects most of the storm, but the couch
is ruined. Similarly, our magnetic shield takes the brunt of
space storms, but some energy continually slips through its
cracks, sometimes enough to cause problems with satellites,
radio communication and power systems,” he said.

“The new knowledge that the cracks are open for long periods,
instead of opening and closing sporadically, can be
incorporated into our space weather-forecasting computer
models to more accurately predict how our space weather is
influenced by violent events on the sun,” said Dr. Tai Phan,
also of UC Berkeley, co-author of the Nature paper.

The solar wind is a stream of electrically charged particles
(electrons and ions) blown constantly from the sun. The solar
wind transfers energy from the sun to the Earth through the
magnetic fields it carries and its high speed (hundreds of
miles/kilometers per second). It can get gusty during violent
solar events, like Coronal Mass Ejections (CMEs), which can
shoot a billion tons of electrified gas into space at millions
of miles per hour.

Earth has a magnetic field that extends into space for tens of
thousands of miles, surrounding the planet and forming a
protective barrier to the particles and snarled magnetic
fields the sun blasts toward it during CMEs. However, space
storms, which can dump 1,000 billion watts, more than
America’s total electric-generating capacity, into the Earth’s
magnetic field, indicated the shield was not impenetrable.

In 1961, Dr. Jim Dungey of the Imperial College, United
Kingdom, predicted cracks might form in the magnetic shield
when the solar wind contained a magnetic field oriented in the
opposite direction to a portion of the Earth’s field. In these
regions, the two magnetic fields would interconnect through a
process known as “magnetic reconnection,” forming a crack in
the shield through which the electrically charged particles of
the solar wind could flow. In 1979, Dr. Goetz Paschmann, of
the Max Planck Institute for Extraterrestrial Physics,
Germany, detected the cracks using the International Sun Earth
Explorer spacecraft. However, since this spacecraft only
briefly passed through the cracks during its orbit, it was
unknown if the cracks were temporary features or if they were
stable for long periods.

In the new observations, the Imager for Magnetopause to Aurora
Global Exploration (IMAGE) satellite revealed an area almost
the size of California in the arctic upper atmosphere
(ionosphere) where a 75-megawatt “proton” aurora flared for
hours. This aurora, energetic enough to power 75,000 homes,
was different from the visible aurora known as the Northern
and Southern lights. It was generated by heavy particles
(ions) hitting the upper atmosphere and causing it to emit
ultraviolet light, which is invisible to the human eye but
detectable by the Far Ultraviolet Imager on IMAGE.

While the aurora was being recorded by IMAGE, the four-
satellite Cluster constellation flew far above IMAGE, directly
through the crack, and detected solar wind ions streaming
through. Normally, these solar wind ions would be deflected by
Earth’s shield, so Cluster’s observation showed a crack was
present. This stream of solar wind ions bombarded our
atmosphere in precisely the same region where IMAGE saw the
proton aurora. The fact that IMAGE was able to view the proton
aurora for more than nine hours, until IMAGE progressed in its
orbit to where it could not observe the aurora, implies the
crack remained continuously open. Estimating from the IMAGE
and Cluster data, the crack was twice the size of the Earth at
the boundary of our magnetic shield, about 38,000 miles
(60,000 km) above the planet’s surface. Since the magnetic
field converges as it enters the Earth in the polar regions,
the crack narrowed to about the size of California down near
the upper atmosphere.

IMAGE was launched March 25, 2000 to provide a global view of
the space around Earth influenced by the Earth’s magnetic
field. The Cluster satellites, built by ESA, and launched July
16, 2000, are making a three-dimensional map of the Earth’s
magnetic field. For images, movies and more information, on
the Internet, visit:

http://www.gsfc.nasa.gov/topstory/2003/1203image_cluster.html