It's a long-standing mystery of physics: "You don't expect a star that's hot in the middle to get hotter as it goes away from the surface," said NASA project scientist Joe Gurman, who works on the Solar TErrestrial RElations Observatory (STEREO) mission. But somehow the sun's surface, around 11,000 degrees, is cool compared to the superheated corona, which reaches millions of degrees. What brings this extra warmth to the sun's atmosphere? In January, scientists said they may have an answer: Plasma fountains called spicules, like those seen here, that shoot up from the chromosphere. That's an area just above the sun's surface. The plasma fountains are as long as Earth and last a few minutes, but a newly observed class of spicules lasts about 100 seconds, moving 186,000 miles per hour. The Solar Dynamics Observatory and the Japanese Hinode spacecraft (meaning "dawn") were able to catch them in action. Scientists at Lockheed Martin's Advanced Technology Center, the National Center for Atmospheric Research and the University of Oslo, Norway, published a paper on the spicules in the journal Science. They found that the heated spicules likely occur often enough to continuously replenish the corona, but there are still plenty of questions — the interface between the surface and the corona is still pretty poorly understood. An upcoming NASA mission scheduled for launch next year will provide some answers (keep reading to find out more). K. Reardon/IBIS
Yesterday, the vernal equinox, the sun returned to the Northern Hemisphere at last. Nothing here or anywhere else in our corner of the galaxy would exist without the sun, yet a surprising number of solar mysteries persist. Much of heliophysics is focused on “space weather,” predicting what the sun will do. That’s because solar flares and coronal mass ejections spew charged particles and radiation into space, occasionally toward Earth. These seething bursts of energy can jeopardize telecommunications on the ground and in space, not to mention the lives of astronauts.
But there are plenty of other, perhaps more profound, burning questions: how does the star actually work? What’s inside it? What, exactly, it is belching out at us?
Ephraim Fischbach, a physics professor at Purdue University, is trying to figure out whether solar particles are messing with radioactive materials on Earth, for instance. Something is definitely happening; it’s just that no one can explain it yet.
New spacecraft like the Solar Dynamics Observatory could help answer some of these questions.
“We’re moving toward a weather-type analysis, what has to happen inside the sun to see what will happen outside the sun. If we get a model for that, we need to test it, and that’s the data the satellites are giving us,” said W. Dean Pesnell, project scientist for the Solar Dynamics Observatory at NASA’s Goddard Space Flight Center. “We are asking people to give us a far more detailed analysis of the sun than other stars or planets.”
In celebration of the sun’s return to the northern hemisphere — and NASA’s Solar Week festivities — here we take a look at some major questions scientists still have about the sun, and the ways new spacecraft are helping answer them.