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Oct.
30, 2008: During the time it takes you to read this
article, something will happen high overhead that until recently
many scientists didn't believe in. A magnetic portal will
open, linking Earth to the sun 93 million miles away. Tons
of high-energy particles may flow through the opening before
it closes again, around the time you reach the end of the
page.
 "It's
called a flux transfer event or 'FTE,'" says space physicist
David Sibeck of the Goddard Space Flight Center. "Ten
years ago I was pretty sure they didn't exist, but now the
evidence is incontrovertible."
Indeed,
today Sibeck is telling an international assembly of space
physicists at the 2008 Plasma Workshop in Huntsville, Alabama,
that FTEs are not just common, but possibly twice as common
as anyone had ever imagined.
Right:
An artist's concept of Earth's magnetic field connecting to
the sun's--a.k.a. a "flux transfer event"--with
a spacecraft on hand to measure particles and fields. [Larger
image]
Researchers
have long known that the Earth and sun must be connected. Earth's
magnetosphere (the magnetic bubble that surrounds our planet)
is filled with particles from the sun that arrive via the solar
wind and penetrate the planet's magnetic defenses. They enter
by following magnetic field lines that can be traced from terra
firma all the way back to the sun's atmosphere.
"We
used to think the connection was permanent and that solar
wind could trickle into the near-Earth environment anytime
the wind was active," says Sibeck. "We were wrong.
The connections are not steady at all. They are often brief,
bursty and very dynamic."
Several
speakers at the Workshop have outlined how FTEs form: On the
dayside of Earth (the side closest to the sun), Earth's magnetic
field presses against the sun's magnetic field. Approximately
every eight minutes, the two fields briefly merge or "reconnect,"
forming a portal through which particles can flow. The portal
takes the form of a magnetic cylinder about as wide as Earth.
The European Space Agency's fleet of four Cluster spacecraft
and NASA's five THEMIS probes have flown through and surrounded
these cylinders, measuring their dimensions and sensing the
particles that shoot through. "They're real," says
Sibeck.
Now
that Cluster and THEMIS have directly sampled FTEs, theorists
can use those measurements to simulate FTEs in their computers
and predict how they might behave. Space physicist Jimmy Raeder
of the University of New Hampshire presented one such simulation
at the Workshop. He told his colleagues that the cylindrical
portals tend to form above Earth's equator and then roll over
Earth's winter pole. In December, FTEs roll over the north
pole; in July they roll over the south pole.
 Right:
A "magnetic portal" or FTE mapped in cross-section
by NASA's fleet of THEMIS spacecraft. [Larger
image]
Sibeck
believes this is happening twice as often as previously thought.
"I think there are two varieties of FTEs: active and
passive." Active FTEs are magnetic cylinders that allow
particles to flow through rather easily; they are important
conduits of energy for Earth's magnetosphere. Passive FTEs
are magnetic cylinders that offer more resistance; their internal
structure does not admit such an easy flow of particles and
fields. (For experts: Active FTEs form at equatorial latitudes
when the IMF tips south; passive FTEs form at higher latitudes
when the IMF tips north.) Sibeck has calculated the properties
of passive FTEs and he is encouraging his colleagues to hunt
for signs of them in data from THEMIS and Cluster. "Passive
FTEs may not be very important, but until we know more about
them we can't be sure."
There
are many unanswered questions: Why do the portals form every
8 minutes? How do magnetic fields inside the cylinder twist
and coil? "We're doing some heavy thinking about this
at the Workshop," says Sibeck.
Meanwhile,
high above your head, a new portal is opening, connecting
your planet to the sun.
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Author: Dr.
Tony Phillips | Credit: Science@NASA
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