"Warm Plasma Cloak" Discovered Enveloping Earth

January 7, 2009

The Earth is dressed in layers that protect it from the sun's fierce winds, and scientists have identified a new one they call a "warm plasma cloak."

The magnetosphere—the shield of ions and electrons that envelops Earth—extends far beyond the atmosphere, defending the planet from the harmful solar wind.

(Related: "Sun's Mysterious Waves Found; May Be Solar Wind Source" [December 6, 2007].)

Charles "Rick" Chappell, a physicist at Vanderbilt University in Nashville, Tennessee, led a research team that assembled information dating back decades to describe the new magnetosphere layer.

Some of the first hints of the cloak first showed up in data from research satellites in the early 1970s. The cloak was finally confirmed by NASA's Polar satellite, which ended a 12-year run in April 2008.

The cloak's discovery creates a theoretical home for particles that didn't fit with any of the other understood parts of the Earth's magnetosphere, Chappell said.

"The cloak particles didn't fit with any of the other regions."

The results appeared in fall 2008 in the Journal of Geophysical Research.

Flying Horseman

Chappell and his colleagues called the layer the "warm plasma cloak" because it conjured an image for them of a person on a horse, wearing a long cloak. Plasma is ionized gas found in space.

The cloak's tails billow in response to the direction of solar winds.

The warm plasma cloak begins thinly on the nightside—or darkside—of the planet and wraps around to the dayside, where it becomes thickest until noon. In the afternoon, convective winds push the cloak out toward the edge of the magnetosphere, where it's peeled off by solar winds.

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