NASA’s Parker Solar Probe Confirms Decades-Old Idea About The Sun

The Sun in the Extreme Ultraviolet during a flare in 2015. NASA/SDO

The Sun is the star we know most about but this doesn’t mean we understand it completely. Many mysteries are yet to be solved and many hypotheses are yet to be tested and confirmed. However, thanks to NASA’s Parker Solar Probe one of these has finally got the corroboration it needed, and it may help us in predicting future potentially dangerous solar events.

As reported in The Astrophysical Journal Letters, NASA’s mission to the study the Sun has provided important insights into the movement of plasma and magnetic fields in the solar atmosphere. These move in a global circulation pattern and their sudden and powerful magnetic interactions accelerate the solar wind into interplanetary space.

The magnetic field coming out of the Sun can be in the form of "open" field lines stretching outwards or "closed" loops, often seen in solar prominences when a loop can be seen erupting out from the Sun. Parker data suggest that these two types of field lines can interact, turning into one another, a phenomenon called interchange reconnection, as one realigns with the other.

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A magnetic field line undergoing interchange reconnection then launching a magnetic field switchback into the corona. Animation by NASA and Levi Hutmacher/University of Michigan Engineering

This phenomenon has dramatic consequences and not for the Sun alone. The abrupt change in magnetic field direction, known as switchback, can accelerate the solar wind and that solar wind is thrown at high speeds towards the planets.

“What this gives us is insight into how the Sun produces slow and fast solar winds,” Professor Justin Kasper, principal investigator for Parker’s Solar Wind Electrons Alphas and Protons (SWEAP) instrument suite, said in a statement. “Defining that mechanism is key to predicting when a transition from slow to fast solar wind is going to strike Earth and create a geomagnetic storm.”

The data from Parker confirms predictions about interchange connections in the Sun's magnetic field lines put forward in 1999 and 2001 by Lennard Fisk, Thomas Zurbuchen, and colleagues. These were based on data from the Ulysses spacecraft, which did not have the resolution to actually see these magnetic field interactions happen.

Illustration of global magnetic field circulation enabled by interchange reconnection. In this scenario an open magnetic field line is (A) dragged against a large coronal loop, by global circulation in the corona, (B) undergoes interchange reconnection, and (C) effectively jumps the approximate width of the originally closed-loop, launching an S-shaped switchback in the magnetic field into the corona. Graphic by Justin Kasper and Levi Hutmacher/University of Michigan Engineering

“It’s amazing to see Parker Solar Probe provide a missing puzzle piece to support and expand ideas we first thought about with spacecraft data from almost 25 years ago,” said Zurbuchen. “As Parker Solar Probe flies closer to the Sun, I can’t wait to see what answers – and questions – we’ll learn next.”

The Parker Solar Probe mission launched in 2018 with the mission to get closer to the Sun than any other spacecraft before it, to study it in detail. Its closest approach to the Sun to date was this past January when it reached just 18.7 million kilometers (11.6 million miles). With every passage around the Sun, it gets closer and closer, and by 2025 will be at about a third of that distance.

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