The Solar Atmosphere is Far Larger Than Once Thought

NASA scientists have discovered that the atmosphere of the Sun is even larger than thought, reaching out an estimated 5 million miles above the star's surface.

According to scientists from NASA's Solar Terrestrial Relations Observatory (STEREO), the solar atmosphere - called the corona - extends to the equivalent of 12 solar radii, potentially impacting future missions to the Sun such as the Solar Probe Plus mission.

"We've tracked sound-like waves through the outer corona and used these to map the atmosphere," Craig DeForest of the Southwest Research Institute in Boulder, Colorado, said in a statement. "We can't hear the sounds directly through the vacuum of space, but with careful analysis we can see them rippling through the corona."

Using STEREO wave data on the inner boundary of the Sun's helioshere and Voyager 1 data on the outer boundary, DeForest and his colleagues were able to fully calculate the entire size of the Sun's corona - an atmosphere characterized by vast amount of plasma particulates, magnetic field swarms, and solar flares.

Initially, researchers had assume that the corona was much smaller in size, but the combined data showed them that events like solar storms or coronal mass ejections (CMEs) could create ripple-like effects around the whole Sun detected even five million miles from the star's surface. Past that point, however, the ripple effects are no longer detected.

"Beyond that boundary... solar material streams away in a steady flow called the solar wind -- out there, the material has separated from the star and its movement can't affect the corona," NASA reports.

Happily, knowing the exact scale of the corona only helps NASA gain confidence about the Solar Probe Plus (SPP) mission, which will send an unmade probe into the inner solar magnetic system in 2018.

"The mission will directly measure the density, velocity and magnetic field of the solar material there, allowing us to understand how motion and heat in the corona and solar wind are generated," said March Velli, a member of the SPP team.

A study detailing these findings was published in The Astrophysical Journal on May 12.