On the dark side of the Earth, space is riddled with giant plasma tornadoes that power shimmering auroras, new observations reveal.
Researchers operating the five spacecraft of NASA鈥檚 mission reported the discovery today at the meeting in Vienna, Austria.
They were measuring how the , a flow of charged particles from the sun, interacts with Earth鈥檚 magnetic field.
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On the Earth鈥檚 dark side, the solar wind stretches out the field, forming a region known as the magnetotail. The magnetotail is like a rubber band; when it is stretched too far, 鈥渆ventually it snaps and releases the energy鈥�, says team member Andreas Keiling of the University of California, Berkeley.
Counter spirals
The sudden energy release creates a pair of counter-spiralling vortices, which THEMIS detected by measuring the speed and direction of the solar wind in the magnetotail. Each one is 70,000 kilometres long and wide enough to envelop the Earth (see illustration).
One vortex in the pair sends particles spiralling along Earth鈥檚 magnetic field lines until they hit molecules of the ionosphere 400 km above the surface. The energy released by the collisions creates the auroral glow, like the gas in a neon light.
Charged particles return up through the other vortex, completing the electrical circuit. The vortices appear every three hours or so, and each one channels a current of 100,000 amps into the ionosphere while it is there.
Little warning
Indeed, magnetometers across North America confirmed that auroral events happened about a minute after THEMIS registered the formation of vortices in the magnetotail. Also, the auroras moved towards the poles in pairs, mirroring the paired vortices in space.
Though the discovery will help researchers understand more about what drives space weather, it won鈥檛 help us avoid the disaster scenarios such weather can cause (see Space storm alert: 90 seconds from catastrophe). 鈥淚t takes about a minute from when the tornado forms for it to propagate down to the ionosphere,鈥� Keiling told 快猫短视频. 鈥淎ny warning has to come before that.鈥�
The observations are limited, and it is not yet proven that all auroras are caused by giant space tornadoes, but Keiling thinks this is likely. 鈥淎 tornado will be involved at some point in the process,鈥� he says.
