The Enigma of the Sun's Superhot Corona, Solved

Astronomers have busted for the first time in the Sun's corona the elusive oscillations called Alfv�n waves, carrying energy outward from the Sun. This could explain the basic behavior of solar magnetic fields and Sun's action on Earth and its whole system.

"Alfv�n waves can provide us with a window into processes that are fundamental to the workings of the Sun and its impacts on Earth," said lead researcher Steve Tomczyk, of the High Altitude Observatory at National Center for Atmospheric Research (NCAR).

The fast moving Alfv�n waves are expelled outward from the Sun along magnetic field lines. They were found in the heliosphere, but never before within the corona, the outermost layer of the Sun's atmosphere visible during a Sun eclipse.
Alfv�n waves are trickier to observe partly because, opposite to other waves, they do not provoke large-intensity fluctuations in the corona and their slow small shifts are hard to detect.

"Our observations allowed us to unambiguously identify these oscillations as Alfv�n waves. The waves are visible all the time and they occur all over the corona, which was initially surprising to us." said coauthor Scott McIntosh of the Southwest Research Institute in Boulder.

The speed and direction of the waves could allow the researchers to assess basic traits of the solar atmosphere, like density and direction of magnetic fields and explain a long standing mystery: why the Sun's corona is hundreds of times hotter than the star's surface.

Now, solar storms could also be better forecast. These storms launch thousands of tons of magnetized matter into the sun system, inducing perturbations in the Earth's magnetic field, that affect sensitive telecommunications and power systems. Increased knowledge could also protect astronauts from dangerous levels of cosmic radiation.

"If we want to go to the moon and Mars, people need to know what's going to happen on the Sun," said Tomczyk.

The team employed the coronal multichannel polarimeter (CoMP), a telescope developed by NCAR in the last years, at the National Solar Observatory in Sacramento Peak, New Mexico, to investigate corona's light, which is much weaker than the Sun's itself. The new technique records magnetic activity of the Sun with an unprecedented rhythm, one track at every 15 seconds.

This way the astronomers could simultaneously determine intensity, velocity and polarization images of the solar corona, tracking down the Alfv�n oscillations moving at about 2,500 mi (4,000 km) per second.