NASA's Parker Solar Probe is expected to provide an answer to a mystery that has been puzzling scientists for hundreds of years.

In two years, the spacecraft is expected to become the first to enter what is called the "zone of preferential heating" above the surface of the sun. In this region, elements are superheated until they are about 10 times hotter than the hydrogen at the core of the yellow dwarf.

"Whatever the physics is behind this superheating, it's a puzzle that has been staring us in the eye for 500 years," stated Justin Kasper, a professor of climate and space sciences at the University of Michigan and the principal investigator behind the mission.

The Sun's Hot Exterior

The sun's corona, the outermost layer of the star's atmosphere, can reach temperatures upward of 2 million degrees Fahrenheit, according to NASA. However, the surface of the sun reaches only about 10,000 Fahrenheit, which is still very hot, but its temperature is significantly lower than that of the corona.

In the same zone, hydromagnetic Alfvén waves (named after Nobel laureate Hannes Alfvén) that bounce around below the Alfvén point, or the outermost edge. At the Alfvén point, the solar winds are faster than the Alfvén speed and the Alfvén waves can no longer travel back to the sun.

Solving The Mystery Of The Sun's Hot Outer Atmosphere

In a study published in The Astrophysical Journal Letters, Kasper and colleagues detailed how they will use the Parker Solar Probe to understand what is making the heavy ions superheat under the Alfvén point. In the paper, the researchers predicted that the spacecraft will reach the zone of preferential heating in 2021 when the Alfvén point and other surfaces expand with solar activity.

"The predictions in this paper suggest that these processes are operating below the Alfvén surface, a region close to the sun that no spacecraft has visited, meaning that these preferential heating processes have never before been directly measured," added Kristopher Klein, one of the authors of the study.

By studying the sun's outer atmosphere, scientists will also be able to better understand and predict solar weather, which can have serious effects to life on Earth.

The Parker Solar Probe was launched in August 2018. It will approach the Sun several times over the next couple of years, each time moving closer toward the surface.

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