There are many places in the solar system that are hotter than the surface of the sun, but contrary to what is expected, the plasma layer of the outer atmosphere of the sun, or the so-called solar corona, is much hotter than its surface.
"It is surprising and surprising that the solar corona is farther from its center, yet it is hotter than its surface," says Jia Hong, an astronomer from the University of California.
The surface temperature of the sun is about 10 thousand degrees Fahrenheit, while the temperature of the corona is about two million degrees Fahrenheit. This scientific dilemma is known as the solar corona heating problem. Astronomers have been working on it since the mid-nineteenth century.
“When we solve this problem, we will have a better understanding of the sun, and we will also understand the heliophysics, which are essential for predicting space weather to protect us,” says Hong. He added, "The sun is the only star to which we can send space probes, because other stars are far away, and when we understand the sun, we will understand the rest of the stars."
A brief history of the emergence of the solar corona hotter dilemma:
In 1869, during a total solar eclipse, astronomers were able to focus on the solar corona and conducted some studies on it, to discover that its temperature is higher than the temperature of the surface of the sun, and they also noticed the presence of a new element, called coronium, which was later called old iron with the emergence of quantum mechanics after nearly 60 years years of its discovery.
This was the oldest known record of measuring the temperature of the solar corona, and it opened the door to a research journey that continues to this day, and raised tantalizing questions such as: Why does the temperature of the plasma rise? Or in other words, where does this energy come from in the aura?
Hong says: «We know that this dilemma does not have a convincing explanation so far, and the astronomical community is still working on solving it, but there are two main hypotheses to solve it, the first is known as motion waves or Alfene waves and the second is known as nanoflares.
The first hypothesis, Alven waves:
The surface of the Sun oscillates and produces bubbles. During convection of the plasma, hotter material rises to the top, while cooler material descends to the bottom, which produces the solar magnetic field.
This magnetic field moves and oscillates in waves called Alfine waves, which push protons and electrons towards the surface of the sun. These waves are known in physics and many experiments have been conducted on Earth. Astronomers believe that the charged particles produced by this phenomenon transfer heat to the solar corona, and its temperature rises to shocking degrees. .
The second hypothesis, nanoflares:
A more dramatic interpretation in which the sun is represented as rolling in a rubber band. When the sun's plasma rotates in its upper layers, it distorts the lines of the magnetic field of the sun, and these lines reach a degree that they cannot bear, and a phenomenon called magnetic reconnection occurs, through which millions of charged particles are sent, which transfer energy to the solar corona, and this event is called nanoflare. Astronomers have observed some nanocomposites in the corona with space telescopes and observatories.
But the mystery of the solar corona's heating still continues, and it is likely that these two phenomena may overlap together, and astronomers cannot yet determine when they will occur, but they will soon obtain more information about them through the Parker probe, which was launched in 2018, and touched the sun a while ago, and this will provide Also a better understanding of the particles responsible for raising the temperature. The probe is currently flying through the heliosphere, but will dive deeper to solve the corona problem. "I'm confident of making great progress in the next decade," Hong says.