Magnetic Portals Connect Earth to the Sun 30 October 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 Centre. "Ten
years ago I was pretty sure they didn't exist, but now the evidence is
incontrovertible." Indeed, Sibeck
told 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.
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
defences. 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.
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. 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
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.