Solar atmosphere much larger than previously thought: NASA

In a significant discovery that will have bearing on NASA's upcoming Solar Probe Plus mission, scientists have found that the sun's corona - the vast atmosphere of solar particles that surround the sun - is even larger than previously thought, extending out some five million miles or eight million km above the sun's surface.

Through the solar particles, magnetic fields swarm, solar flares erupt, and gigantic columns of material rise, fall and jostle each other around.

Scientists used NASA's Solar Terrestrial Relations Observatory (STEREO) to measure the more accurate size of the corona.

"We have tracked sound-like waves through the outer corona and used these to map the atmosphere," said Craig DeForest of Southwest Research Institute in the US.

"We cannot hear the sounds directly through the vacuum of space, but with careful analysis we can see them rippling through the corona," DeForest added.

Solar Probe Plus mission is due to launch in 2018. The mission will try to go closer to the sun than any man-made technology ever has before.

These stereo observations provide the first direct measurements of the inner boundary of the heliosphere - the giant bubble filled with solar particles that surrounds the sun and all the planets.

The researchers studied Alfven waves or magnetosonic waves - a hybrid of sound waves and magnetic waves - which oscillate about once every four hours -- and are about 10 times the length of earth.

The results appeared in the Astrophysical Journal.