Magnetic Portals Connect Sun and Earth
10.30.2008
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.
http://science.nasa.gov/headlines/y2008/30oct_ftes.htm?list759634
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