NASA's Space Place
The Sun’s Supersized Atmosphere
Alex H. Kasprak
National Aeronautics and Space Administration
Like Earth, the sun has an atmosphere with layers in it. The outermost layer is called the corona, and it’s a wild mess of activity. Scientists have long known about the corona. It is home to some spectacular shows—giant eruptions called Coronal Mass Ejections, loops, prominences, and massive magnetic storms.
Using NASA data, scientists recently made a shocking discovery about this solar region. It’s much bigger than they thought! While the sun is nearly 900,000 miles wide, the corona actually extends five million miles above the sun’s surface. In other words, the sun’s atmosphere is six times wider than the sun itself!
Scientists made this discovery by looking at waves rippling through the area surrounding the sun. These waves are called magnetosonic waves. They can be seen passing through the corona as they move away from the sun. Once the corona becomes too thin, they can no longer be viewed. No more wave? No more corona!
These magnetosonic waves are pretty wild, too. They are a bit like sound waves and a bit like a weird kind of magnetic wave. Sound waves cannot be heard in space, since there is nothing for them to pass through to get to Earth. And sound waves are too small to be viewed from afar. Magnetosonic waves, though, are about 10 times the length of Earth. With some clever work, scientists figured out a way to see them with a pair of NASA satellites in orbit around the sun.
The discovery that the corona is so large is an important one. Before this discovery, scientists thought they had a pretty good idea where the sun’s atmosphere ended and where the rest of space began. They couldn’t be happier that they were wrong.
That’s because NASA is working on a new spacecraft that will travel to the sun. It will go closer to the sun than any previous mission. When NASA started working on it, they weren’t sure if it would actually travel through the corona itself. With this new discovery, they now know for sure that it will!
The corona is still full of unanswered questions. Read about one of the corona’s more confusing mysteries at NASA’s Space Place:http://spaceplace.nasa.gov/sun-corona.
Images from NASA’s Solar Terrestrial Relations Observatory that show waves traveling through the corona. The sun itself is blocked out to make the corona easier to view. Credit: NASA/STEREO.