Here is something strange about the sun that you have probably never considered, as I heard it from Justin Kasper, an astrophysicist who studies our star at the Harvard-Smithsonian Center for Astrophysics.
The sun is powered by fusion reactions at its core in which hydrogen atoms fuse together into helium, releasing tremendous energy in the process. That energy moves out from the core to the surface of the sun, called the photosphere. The temperature there is about 10,000 degrees Fahrenheit.
As you continue to move out from the sun, we cross upwards into the corona, where a very strange thing happens: the temperature jumps to a million degrees. That is to say, the atmosphere of the sun is thousands of times hotter than its surface.
To consider how weird this is, imagine you light your stove and the area farther away from the heat source is actually hotter than the regions closer in. That's not normally how heat flows. And yet, on the sun, that is exactly how it works, and scientists just aren't sure why.
Kasper called it "the mystery of the sun's corona" here at the Aspen Ideas Festival in making his pitch for the importance of a mission to fly an instrument into the sun's corona to take direct measurements. They call it the Solar Probe Plus, and he hopes it will launch in 2018. The mission would follow the about-to-launch NASA satellite IRIS, which will be studying the interface between the surface and corona from the safety of earth orbit.