NASA STEREO Reveals the Sun Has a Much Larger Atmosphere Than Previously Thought

Learning more about our sun's atmosphere is an important part of understanding the space weather that can impact our own planet. Now, scientists have found that this atmosphere, called the corona, is even larger than thought and extends about five million miles above the sun's surface.

In this case, the researchers used NASA's Solar Terrestrial Relations Observatory (STEREO) in order to better study the vast atmosphere of solar particles through which magnetic fields swarm. This allowed them to gather the first direct measurements of the inner boundary of the heliosphere, which is the giant bubble sparsely filled with solar particles that surrounds the sun and all the planets. This allowed the researchers to determine the extent of the entire local bubble.

More specifically, the researchers studied waves known as magnetosonic waves, which are a hybrid of sound waves and magnetic waves called Alfven waves. Unlike sound waves on Earth, these waves oscillate once every four hours and are about 10 times the length of Earth.

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

After tracking these waves, the scientists found that the material throughout this extended space remained connected to the solar material much further in. About five million miles from the sun, giant solar storms and coronal mass ejections could create ripple effects felt through the corona. Beyond this bounder, solar material streamed away in a steady flow called the solar wind.

Understanding exactly how far the corona extends is important for future missions to our nearest sun, including NASA's Solar Probe Plus. This mission plans to travel to within four million miles of the sun, which means that it will be traveling through the solar corona. This, in turn, will provide scientists with further data about the sun.

"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 g enerated," said Marco Velli, a Solar Probe Plus scientist, in a news release."

The findings are published in The Astrophysical Journal.