NASA’s goal of conquering the Sun

Our sun is the best-studied star in the universe. However, there is a big mystery that remains unsolved. The Sun’s surface is about 6,000 degrees Celsius, but its outermost layer of atmosphere, called the corona, is incredibly hotter – about 1 million degrees Celsius.

The corona can be seen as a halo surrounding the shadow of the Sun during a total solar eclipse. To solve the mystery of the temperature of the corona, scientists built the Parker probe. This spacecraft flies around the Sun, goes deep into the corona, collecting data showing that small magnetic field activities inside the Sun’s atmosphere make the corona so hot that it is difficult to imagine.

The high temperature of the corona is related to the Sun’s magnetic activity. About 200,000 km below the Sun’s surface is a magnetic field “machine” that governs stellar activity. This activity strengthens and weakens in a cycle of about 11 years. When the Sun is active, activities such as solar storms and sunspots will increase in intensity and frequency.

On the Sun’s surface, magnetic fields concentrate at the boundaries of rolling convection zones, looking like bubbles in a pan of boiling oil. The Sun’s surface is constantly vibrant, causing these magnetic fields to strengthen at the edges of convection zones. The amplified magnetic fields then release plasma jets and small bursts as they interact with the solar plasma.

Normally, the temperature will gradually decrease as you move away from the heat source. But with the Sun, the corona region – the outermost part of the Sun’s atmosphere – has a much higher temperature than the surface.

Scientists have proposed many different hypotheses to explain this. Some argue that heat transfer in the corona is the same as in a liquid, with turbulent flows transferring heat from larger areas to smaller areas. Others think that magnetic waves from the Sun’s surface continuously fluctuate and transfer heat to the atmosphere, or that high temperatures are related to the instability of matter particles.

In 1988, astrophysicist Eugene Parker proposed an interesting hypothesis. He suggested that convective movements on the Sun’s surface could entangle magnetic field lines extending into the corona, storing magnetic energy there. When these magnetic field lines break and reconnect, the energy released heats the corona to high temperatures, causing “nanoflares”.

Parker’s hypothesis is reasonable but lacks data to verify. Previous ways of studying the Sun were not enough to solve this problem.

In 2005, a turning point came. Solar and solar wind scientists gather to share data from telescopes, rockets, the ESA SOHO satellite and other NASA satellites. The goal is to combine research to solve the mystery of the corona’s high temperatures and the process by which it accelerates the solar wind.