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The solar corona, the aura of plasma that surrounds the Sun, holds a huge mystery. It is much hotter than the surface of the Sun, and we don’t know exactly how that's possible. Many theories have been suggested to explain the coronal heating problem, but we don’t have an agreed solution. Now, a new discovery might provide what solar scientists need to explain the conundrum.
The team has discovered that iron ions appear to get trapped by magnetic fields and electrical currents in regions near the solar surface. Since the corona is studied by monitoring these ions, it is possible that we are missing energetic events that start on the solar surface that heat up the corona. The findings are published in the Astrophysical Journal.
The solar surface has a temperature of about 5,500°C (10,000°F), but the corona can be millions of degrees. To measure the temperature of the corona, scientists look at what elements have lost electrons and have become ionized. At those high temperatures, it’s the heaviest elements like iron that can be spotted by our high-energy telescopes. This study suggests that more energy might be going in the corona than previously thought.
"We knew that something really intriguing happens at the interface between the photosphere – the Sun's surface – and the corona, given the noticeable disparities in the chemical composition between the two layers and the sharp rise in plasma temperatures at this junction," lead author Professor Gregory Fleishman, from the New Jersey Institute of Technology, said in a statement.
The ion traps identified in the study are at the base of coronal loops – the gigantic arcs of electrified plasma directed by the strong magnetic field of the Sun’s surface. The team used NASA’s Solar Dynamics Observatory to discover the ion traps. This combined with the latest measurements of electric and magnetic fields of the Sun gives researchers a more complete picture of what’s going on.
"Prior to these observations, we have only accounted for the coronal loops filled with heavy ions, but we could not account for flux tubes depleted of them," Fleishman added. "Now all of these poorly understood phenomena have a solid physical foundation that we can observe. We are able to better quantify the corona's thermal structure and gain a clearer understanding of why ion distribution in the solar atmosphere is non-uniform in space and variable in time."
This research provides much-needed insights into the complex behavior of our Sun and will hopefully help astronomers finally explain the mysteries of the solar corona.