NASA's Parker Solar Probe finds fresh clues to decades-old mystery surrounding the sun

For decades, scientists have puzzled over why the sun's outer atmosphere, or corona, heats up as it moves further from the sun's surface.

Now the long list of possible explanations has been trimmed down by one thanks to data collected by NASA's Parker Solar Probe, the fastest human-made object, which has repeatedly skimmed the sun as it hunts for clues to solve the so-called "coronal heating mystery."

During the probe's first brushes past the sun, its instruments detected abrupt reversals in the direction of the sun's magnetic fields. Scientists call such instances "switchbacks" and suspect they play a role in heating the corona, primarily by releasing magnetic energy packed within them as they move within the sun and in space.

"That energy has to go somewhere, and it could be contributing to heating the corona and accelerating the solar wind," study co-author Mojtaba Akhavan-Tafti of the University of Michigan said in a statement.

The coronal heating mystery refers to the fact that the sun's outer atmosphere, the corona, is hundreds of times hotter than its "surface," the photosphere. That is despite the fact the photosphere is millions of miles closer to the sun's core where the nuclear fusion that provides our star's heat and energy occurs.

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Despite being cooler than the corona, the photosphere is responsible for the vast majority of the light from the sun, completely "washing out" light from the solar atmosphere. Thus, the solar corona can only be seen when light from the photosphere is blocked by an eclipse or by using a special instrument called a coronagraph.