Polar auroras

The wind of charged particles blowing from the Sun to Earth carrying a powerful magnetic field is able to cross the Earth’s magnetosphere: the comparison between the data of the ESA mission Cluster and NASA images finally gave an explanation of the luminescence spectacular Theta Aurora polar.
Seen in satellite images, it seems to clearly draw the outlines of the Greek letter theta. And it is with the name of Theta Aurora that is known by scientists. There are some spectacular auroras that light up the sky at 65-70 degrees north and south of the equator. A green glow and, more rarely, red. Now, thanks to the data collected by the ESA Cluster mission and NASA satellite images, we finally have an explanation of what are the origins of this impressive natural spectacle.


Credit: NASA/ESA

The wind of charged particles blowing from the Sun to Earth and other planets of the system to which we belong, carries with it a part of the magnetic field of our star, powerful enough to cross the Earth’s magnetosphere.
When two areas of electrically charged gas (plasma) and magnetic fields collide in different directions, the structures of the fields can be altered, breaking and reconnecting in a new shape that changes the topography of departure. The action between the two magnetic fields can feed an eruption on the surface of the star, or change the energy with which the solar wind caresses the Earth’s atmosphere and giving rise to the spectacle of the aurora polar that enchants the arctic night.
When a collision occurs between two regions of plasma having the same density, temperature and magnetic field strength – but different orientation – it has an immediate symmetrical reconnection. However, more often this type of collisions take place between regions of the plasma with characteristics very different from each other, which happens regularly when the solar wind meets the space around the Earth.


Credit: NASA/ESA

The Theta Aurora fully included among the types of events that may take shape in the sky Arctic (and Antarctic). Robert Fear, University of Southampton in the UK and first author of the just published in Science, has been working on the data collected by the four satellites of the European Space in the Cluster mission, a constellation of satellites that study the Earth’s magnetosphere, which as a shield deflects the solar wind. Cluster measurement is done in three dimensions, the interactions between the Earth’s magnetic field and the solar wind, registering variations and interactions of stellar objects near Earth, including phenomena such as the aurora or electrical discharges.

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