Dear Friends,
Leaks Found in Earth's Protective Shield
Crystal Gammon, OurAmazingPlanet Contributor -
Oct 31, 2012
09:47 AM ET
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When Earth’s magnetic field and the interplanetary
magnetic field are aligned, for example in a northward orientation as
indicated by the white arrow in this graphic, Kelvin–Helmholtz waves are
generated at low (equatorial) latitudes. CREDIT: AOES Medialab |
Our planet's protective magnetic bubble may not be as protective as
scientists had thought. Small breaks in Earth's magnetic field almost
continuously let in the solar wind — the stream of magnetic, energized
plasma launched by the sun toward the planets — new research has found.
"The solar wind can enter the magnetosphere
at different locations and under different magnetic field conditions
that we hadn't known about before," Melvyn Goldstein, an astrophysicist
at NASA's Goddard Space Flight Center, said in a statement.
Charged particles in the solar wind can interrupt GPS signals and power systems, as well as create dazzling auroras.
The magnetosphere is the planet's first line of defense against the
solar wind. Scientists knew that this plasma stream occasionally
breached the magnetosphere near the equator, where the Earth's magnetic
field is roughly parallel to the magnetic field in the solar wind.
The new study, published Aug. 29 in the Journal of Geophysical
Research, found that these breaks can happen under a wider range of
conditions.
"That suggests there is a 'sieve-like' property of the magnetopause
[the outer edge of the magnetosphere] in allowing the solar wind to
continuously flow into the magnetosphere," Goldstein said.
Plasma swirls break magnetic field
The European Space Agency's Cluster mission, a set of four satellites that fly in close formation through the Earth's magnetic field,
gathered the data that show how the solar wind can get through.
Equipped with state-of-the-art instruments for measuring electric and
magnetic fields, the Cluster satellites fly in and out of the
magnetosphere and document the microscopic magnetic interactions between
the Earth and the sun.
From 2006 Cluster observations, scientists found that huge swirls of
plasma along the magnetopause could help the solar wind penetrate the
magnetosphere when the terrestrial and solar wind magnetic fields were
aligned. Those swirls of plasma are known as Kelvin-Helmholtz waves, and
they can be 24,850 miles (40,000 kilometers) in diameter.
As Kelvin-Helmholtz waves slide past the magnetopause, they can create
giant vortices, similar to how wind blowing across the ocean causes
waves. The huge waves can spontaneously break and reconnect magnetic
field lines, creating openings that let the solar wind slip through.
When
the interplanetary magnetic field, indicated by the white arrow, is
oriented westward (dawnward) or in the opposite, eastward (duskward)
direction, magnetopause boundary layers at higher latitude become most
subject to Kelvin–Helmholtz instabilities.
'Not a perfect magnetic bubble'
The new findings suggest that these magnetic field line breaks can also
occur where the terrestrial and solar wind magnetic fields are
perpendicular, at high latitudes near the poles.
The alignments of the solar wind magnetic field and Earth's magnetic
field are key factors. A perpendicular alignment makes the boundary
between the two fields less stable and likely generates more
Kelvin-Helmholtz waves — and more magnetic field breaches. [Video: Sun's Energy Shocks Earth's Magnetic Field]
"We found that when the [solar wind] magnetic field is westward or
eastward, magnetopause boundary layers at higher latitude become most
subject to Kelvin-Helmholtz instabilities, regions quite distant from
previous observations of these waves," Kyoung-Joo Hwang, a researcher at
NASA's Goddard Space Flight Center who led the study, said in a
statement.
"In fact, it's very hard to imagine a situation where solar wind plasma
could not leak into the magnetosphere, since it is not a perfect
magnetic bubble," Hwang said.
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