One of the most dramatic and mysterious features of the sun are "spicules" -- narrow, high speed jets of plasma that shoot out of the Sun at 44,000 mph, reaching thousand of miles in height before collapsing. At any given time, more than a quarter million spicules are scattered over the surface of the Sun.
We've been aware of the phenomenon for over a century without knowing what causes them.
There were many theories -- that they were caused by soundwaves, or that they were due to a magnetic field forming loops out of the solar atmosphere, among others. These theories only explain bits of the information. Scientists wanted to know the origin of the phenomenon and why these are found all over the Sun.
"It's been very hard to get a clear view of what these spicules do, as Earth's atmosphere creates a murky picture," said Lockheed and Martin Solar and Astrophysics Laboratory principal physicist Bart de Pontieu. "But thanks to space telescopes, we can now see what they really look like in greater detail."
Scientists were interested in how the spicules formed and why the outer atmosphere of the Sun is actually hotter than its surface.
About every five minutes, spicules shoot red hot streams of charged particles into the corona, the outer layer of the solar atmosphere, at around 150 kilometres per second. This is why the Sun's corona, its outer atmosphere is actually hotter than the surface of the Sun. There is a constant supply of hot plasma delivered by the spicules.
After observing the spicules through a powerful telescope, scientists were able to formulate a computer model of what is actually happening in the corona of the Sun. The churning plasma interacts with magnetic fields on the surface of the Sun. The plasma gets twisted up and knotted in the process. This creates strong magnetic tension trapped close to the surface.
Next, "ambipolar diffusion" occurs. That happens when neutral and charged particles mix above the surface. This creates an escape route for the building magnetic tension. The magnetic tension is released into space at very fast speeds.
"These jets of plasma are ejected so fast that they could traverse the length of California in just a couple of minutes," said De Pontieu. "They can reach heights of roughly the diameter of Earth."
To see if their simulations mirrored the real thing on the Sun, the team analysed data from NASA's Interface Region Imaging Spectrograph and the Swedish Solar Telescope. They found that the simulations matched the size, shape and speed of the actual spicules observed through these telescopes.
"It's exciting because it explains why the solar atmosphere is millions of degrees hotter than the surface," said De Pontieu.
Now that they have unlocked the secret of solar spicules. The team wants to see how these spicules interact with the outer reaches of the solar atmosphere.