Scientists
have found two large leaks in Earth's magnetosphere, the region around our
planet that shields us from severe solar storms.
The leaks
are defying many of scientists' previous ideas on how the interaction between Earth's
magnetosphere and solar wind occurs: The leaks are in an unexpected
location, let in solar particles in faster than expected and the whole
interaction works in a manner that is completely the opposite of what
scientists had thought.
The
findings have implications for how solar
storms affect the our planet. Serious storms, which involved charged
particles spewing from the sun, can disable satellites and even disrupt power
grids on Earth.
The new
observations "overturn the way that we understand how the sun's magnetic
field interacts with the Earth's magnetic field," said David Sibeck of NASA's
Goddard Space Flight Center in Greenbelt, Md., during a press conference today
at the annual meeting of the American Geophysical Union in San Francisco.
The bottom
line: When the next peak of solar activity comes, in about 4 years, electrical
systems on Earth and satellites in space may be more vulnerable.
How it
works
Earth's magnetic
field carves out a cavity in the sun's onrushing field. The Earth's
magnetosphere is thus "buffeted like a wind sock in gale force winds,
fluttering back and forth in the" solar wind, Sibeck explained.
Both the
sun's magnetic field and the Earth's magnetic field can be oriented northward
or southward (Earth's magnetic field is often described as a giant bar magnet
in space). The sun's magnetic field shifts its orientation frequently,
sometimes becoming aligned with the Earth, sometime becoming anti-aligned.
Scientists
had thought that more solar particles entered Earth's magnetosphere when the
sun's field was oriented southward (anti-aligned to the Earth's), but the
opposite turned out to be the case, the new research shows.
The work
was sponsored by NASA and the National Science Foundation and based on
observations by NASA's THEMIS
(Time History of Events and Macroscale Interactions during Substorms)
satellite.
How many
and where
Essentially,
the Earth's magnetic shield is at its strongest when scientists had thought it
would be at its weakest.
When the
fields aren't aligned, "the shield is up and very few particles come in,"
said physicist Jimmy Raeder of the University of New Hampshire in Durham.
Conversely,
when the fields are aligned, it creates "a huge breach, and there's lots
and lots of particles coming in," Raeder added, at the news conference.
As it
orbited Earth, THEMIS's five spacecraft were able to estimate the thickness of
the band of solar
particles coming when the fields were aligned — it turned out to be about
20 times the number that got in when the fields were anti-aligned.
THEMIS was
able to make these measurements as it moved through the band, with two
spacecraft on different borders of the band; the band turned out to be one
Earth radius thick, or about 4,000 miles (6,437 kilometers). Measurements of
the thickness taken later showed that the band was also rapidly growing.
"So
this really changes our understanding of solar wind-magnetosphere coupling,"
said physicist Marit Oieroset of the University of California, Berkeley, also at the press conference.
And while
the interaction of anti-aligned particles occurs at Earth's equator, those of
aligned particles occur at higher latitudes both north and south of the
equator. The interaction is "appending blobs of plasma onto the Earth's
magnetic field," which is an easy way to get the solar particles in, said Sibeck,
a THEMIS project scientist.
Next
solar cycle
This
finding not only has implications for scientists' understanding of the
interaction between the sun and Earth's magnetosphere, but for predicting the
effects to Earth during the next peak in the solar cycle.
The Sun
operates on an 11-year cycle, alternating between active and quiet periods. We
are currently in a quiet period, with few sunspots on the sun's surface and
fewer solar flares, though the next
cycle of activity has begun. It is expected to peak around 2012, bringing
lots of sunspots, flares and coronal mass ejections (CMEs). CMEs can interact
with the Earth's magnetosphere, causing problems for satellites,
communications, and power grids.
This
upcoming active period now looks like it will be more intense than the previous
one, which peaked around 2006, some scientists think. The reason is the changes
in the sun's alignment.
During the
last peak, solar fields hitting the Earth were first anti-aligned then aligned.
Anti-aligned fields can energize particles, but in this case, the energy came
before the particles themselves, which doesn't create much of a fuss in terms
of geomagnetic storms and disruptions.
But the
next cycle will see aligned, then anti-aligned fields, in theory amplifying the
effects of the storms as they hit.
Raeder
likens the difference to igniting a gas stove one of two ways: In the first
way, the gas is turned on and the stove is lit and you get a flame. In the
other way, you let the gas run for awhile, so that when you add the gas you get
a much bigger boom.
"It
should be that we're in for a tough time in the next 11 years," Sibeck
said.
advertisement
