A "magnetic portal" or FTE mapped in cross-section by NASA's fleet of THEMIS spacecraft (Credit: NASA)

The fact that a sun-earth connection exists is no big surprise. Since earth’s magnetosphere is filled with particles from the sun, carried by the solar wind, there must be a connection allowing them through. The mechanism of the particle transfer has recently become clearer, and was presented at the 2008 Plasma Workshop in Huntsville, Alabama.

 

On the side of earth closest to the sun, earth's magnetic field presses against the sun's magnetic field. Approximately every eight minutes, the two fields merge briefly, creating a tunnel through which particles may pass. This magnetic cylinder is about as wide as Earth. The European Space Agency's four Cluster spacecrafts and NASA's five THEMIS probes have flown through and around these tunnels, measuring their dimensions and sensing the particles that pass through, verifying these events.

This channeling is called a flux transfer event, or FTE. Space physicist David Sibeck of the Goddard Space Flight Center said, "Ten years ago I was pretty sure they didn't exist, but now the evidence is incontrovertible.” Not only do they exist, they seem to be happening in a different manner than previously suspected. "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.” 

An artist's concept of Earth's magnetic field connecting to the sun's; an FTE, with a spacecraft on hand to measure particles and fields. (Credit: NASA)

The Cluster and THEMIS measurements can be used by theorists to create computer simulations of the FTEs. These simulations can offer possible scenarios as to the events’ behavior and effects. University of New Hampshire space physicist Jimmy Raeder presented such a simulation at the Plasma Workshop. He explained that the magnetic portals tend to form above Earth's equator and then roll over Earth's winter pole. This means that in December they roll over the North Pole and in July they roll over the South Pole.

Sibeck says there seem to be two kinds of FTEs. "I think there are two varieties of FTEs: active and passive." Active FTEs are magnetic tunnels allowing particles to flow through rather easily, and are important energy conduits for Earth's magnetosphere. Passive FTEs are magnetic tunnels offering more resistance due to their internal structure that do not admit such an easy flow of particles and fields. Sibeck has calculated the properties of passive FTEs and is encouraging his colleagues to look for them in THEMIS and Cluster data. "Passive FTEs may not be very important, but until we know more about them we can't be sure.”

Additional questions regarding the FTEs, both the passive and active types, remain. Why do they occur every eight minutes? How do the magnetic fields in the tunnel behave? These questions were addressed at the workshop and additional work will be needed before they are answered.

TFOT reported on Space Shuttle Discovery’s photograph of the Aurora Borealis, also known as the Northern Lights, which are caused by an interaction between particles from the sun and the Earth’s magnetosphere. TFOT also covered the release of photos of the Solar Corona taken with the Hinode space telescope. The Solar Corona is a plasma from which solar wind originates and X-rays are emitted.

 

The full report on the FTEs can be found in the NASA press release.