Scientists Discover the Origins of the Spectacular Theta Aurora

Scientists have solved a long-standing mystery in space. They've uncovered the origin of the "theta aurora," an aurora that occurs at startlingly high latitudes on Earth.

Auroras appear in stunning colors in Earth's northern latitudes. These colorful light displays are actually the most visible manifestation of the sun's effect on Earth; they're caused by the solar wind, a stream of plasma from the sun, that interacts with Earth's magnetic field. Normally, auroras appear in the "auroral oval," which lies at around 65 to 70 degrees north or south of the equator, encircling the polar caps.

 Yet some auroras occur at even higher latitudes. One of these is known as the "theta aurora;" seen from above, it looks like the Greek letter theta-an oval with a line crossing through its center.

In order to find out the origin of theta auroras, the researchers watched particles in two "lobe" regions of the magnetosphere. The plasma in the lobes is normally cold, but previous observations suggested that theta auroras are linked with unusually hot lobe plasma.

The scientists studied data collected simultaneously by the ESA's Cluster and NASA's IMAGE satellites. This revealed uncharacteristically energetic plasma in the lobe.

"We found that the energetic plasma signatures occur on high-latitude magnetic field lines that have been 'closed' by the process of magnetic reconnection, which then causes the plasma to become relatively hot," said Robert Fear, one of the researchers, in a news release. "Because the field lines are closed, the observations are incompatible with direct entry from the solar wind. By testing this and other predictions about the behavior of the theta aurora, our observations provide strong evidence that the plasma trapping mechanism is responsible for the theta aurora."

The findings reveal how these auroras form, and show the intriguing process that takes place in the magnetosphere.

The findings are published in the journal Science.

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