Solar Orbiter catches the sun’s missing high-speed vibrations

The sun’s magnetic fields are a twisty, curvy, ever-changing mess. In particular, our star’s polar regions host areas called polar coronal holes, which contain invisible magnetic highways that stretch into interplanetary space. But there’s a lot we don’t know about how those highways actually work, particularly how they give the particles that form the fast solar wind an extra “kick” that sends them zooming at hundreds of kilometers per second.

A new paper from a team led by Dr. Yuhang Gao and Professor Hui Tian at Peking University, published recently in the journal National Science Review, suggests they might have found an answer by using high-speed images from the Solar Orbiter to detect never-before-seen rapid, high-frequency magnetic waves in those areas.

Key to this discovery is camera speed. Older instruments, such as NASA’s Solar Dynamics Observatory (SDO), took pictures every 12 seconds and had a spatial resolution of around 1,100 km for every pixel. Upgraded equipment offered much faster, higher-resolution imagery. Solar Orbiter’s Extreme Ultraviolet Imager (EUI) captures an image every five seconds, with details down to 420 km per pixel—more than double the precision and twice the speed of earlier instruments.

Using data from both instruments from September 2021, the authors subjected the data to an automated magnetic wave-tracking program called the Northumbria University Wave Tracking (NUWT). Taking a close look at solar plumes—ray-like magnetic structures that stick out from the sun’s north pole—the authors noted a distinct difference in the number of waves detected by the two observatories. With the SDO, the algorithm caught 560 wave events, whereas with the EUI, it caught 2,318—more than four times as many.

The difference seemed to come down to frequency. Thirty-eight percent of the waves seen by the EUI had wavelengths shorter than 100 seconds, whereas only 9% of the waves detected by the SDO had the same wavelengths. Another determining factor was speed—how fast the plasma thread moved. The SDO’s average speed was around 9.9 km/s, whereas the EUI’s averaged 15.4 km/s. And since energy scales with velocity, these faster-moving waves carry much more power. Based on the paper’s calculations, these faster-moving waves carry 2.6 times as much power as previous estimates.

Theories abound about where these types of magnetic ripples come from. The researchers offer three potential sources. The first is when magnetic loops run into unconnected magnetic field lines, causing the lines to snap and reconfigure while simultaneously launching high-frequency ripples into space. A second explanation is that they form as part of a giant jet of plasma called a spicule, which can directly pump these fast transverse waves into the plumes above them. A third explanation is that larger, slower-moving waves might bounce off each other, creating “turbulent cascades” of smaller, higher-frequency waves.

While their creation mechanisms are still somewhat unclear, these waves could help answer two interconnected solar physics mysteries: Why is the outer layer of the sun so hot, and how do the particles from the fast solar wind get accelerated to such incredible speeds? According to the paper, the fast waves that travel into the sun’s upper atmosphere undergo effects such as resonant absorption and phase mixing, transferring much of their energy into the surrounding environment.

Some of that energy is likely translated directly into the heat that drives the absurd temperatures in the sun’s outer layers, which can reach more than 1,000,000℃ (1,800,000°F). Still more of that energy can potentially be transferred directly into the kinetic processes that propel the ions to the speeds needed to form the fast solar wind.

To be clear, these mechanisms aren’t yet well-defined, and the overall energy calculated as part of this single data set is still around an order of magnitude lower than what other models suggest would be needed to fully launch the solar wind. However, the findings show that a massive amount of energy is hiding in plain sight behind the limitations of our technology.

That technology still has room for improvement, with missions like the planned Solar Polar-orbit Observatory (SPO) expected to launch in early 2029. With its unique viewing angle, it will offer unprecedented insights into the magnetic chaos happening at the sun’s poles. Its instruments might even be fast enough to capture more high-energy waves and help solve those mysteries once and for all.

Who’s behind this story?

Lisa Lock

BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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