What fuels the solar wind particles on their way to the Earth and beyond?

Written by Dr. Shirsh Lata Soni, Postdoctoral Research Fellow at University of Iowa, IA, USA

A wind that never stops…

We know the Sun is the main source of energy for our solar system. It emits heat as solar radiation, which reaches even the most distant objects and directly or indirectly drives their natural processes. For example, most natural phenomena on Earth, such as weather patterns and the water cycle, as well as the current phases of evolution, are powered by solar energy.

Beyond light and heat, the Sun also constantly releases streams of tiny, energetic particles, mainly electrons and protons, traveling at speeds between 300 and 800 km per second. This continuous outflow is known as the solar wind, and it typically takes 1 to 3 days to reach Earth. Though invisible, the solar wind is always present in outer space and plays a crucial role in shaping Earth’s outer atmosphere and influencing a wide range of atmospheric and space-related processes.

A Scientific Puzzle: Why Are the Particles Gaining Energy?

As these tiny particles have a huge impact on the current form of our life, they have caught the attention of space researchers. They observed these particles at different locations in space (depicted in Figure 1) and found that their energy increases along their path, whereas basic understanding suggests they should slow down over time and their energy should decrease. This has now become an open question for researchers. Figuring out why this happens can also help us better understand how the Sun behaves and how it affects the space around us.

The Magnetic Clue: What Are Switchbacks?

Along with the solar wind, the Sun also stretches out its magnetic field across the solar system. A possible clue to the solar wind’s strange behavior comes from unusual magnetic twists in this field, known as switchbacks (see Figure 1). These are sudden, zigzag-shaped bends in the Sun’s magnetic field, first clearly observed by NASA’s Parker Solar Probe as it ventured closer to the Sun than any spacecraft before it. Scientists believe these magnetic twists could be a key reason why the solar wind gains extra energy as it moves away from the Sun.

“Imagine the Sun flinging out invisible zigzags of magnetic energy, sharp twists shooting across space at hundreds of kilometers per second. For the first time, researchers have been able to watch these switchbacks gradually smooth out and relax as they travel farther from the Sun, while surprisingly giving the surrounding solar wind a boost in speed. It’s a bit like a compressed spring that expands and releases energy as it returns to its normal shape.”

A rare observation by NASA’s Parker Solar Probe and ESA’s Solar Orbiter

This was made possible when two spacecraft, NASA’s Parker Solar Probe and the European Space Agency’s Solar Orbiter, became radially aligned in their orbits around the Sun. Acting like a celestial relay team, the probes captured similar parcels of solar wind at two different distances from the Sun, offering a rare glimpse into how the solar wind evolves as it moves outward.

Magnetic switchbacks are like the Sun’s fingerprints; they reveal the hidden energy processes shaping the solar wind and influencing the entire solar system, including us here on Earth. These magnetic switchbacks fade and change as they travel farther from the Sun. It helps us understand how the solar wind speeds up and what role the Sun’s magnetic energy plays in it.

Key Finding:

The study showed that the magnetic switchbacks seen by Parker Solar Probe close to the Sun were significantly relaxed by the time they reached Solar Orbiter, farther out in space. During this transition, the surrounding solar wind particles were moving faster, evidence that the switchbacks were transferring magnetic energy outward in the form of kinetic energy.

Why Does This Matter for Us on Earth and What’s Next?

The solar wind affects Earth in many ways: it shapes auroras, disrupts satellite signals, and can even knock out power grids. Understanding how it evolves could help scientists better forecast space weather, the Sun-driven storms that ripple through our solar system.

The research team believes that a process called magnetic relaxation is at play: the intense twists in the magnetic field gradually release energy, transferring it into accelerating the solar wind. It’s a step toward solving a larger puzzle: how the solar wind gains energy and heat as it moves away from the Sun, even though it should be cooling down.

As Parker Solar Probe and Solar Orbiter continue their daring missions, diving deeper into the Sun’s domain, scientists are hopeful that more alignments like this one will help decode the mysteries of our star and its ever-blowing wind.

Stay tuned, the solar wind has more secrets to reveal.

Reference: 

[1]. “Switchback patches evolve into microstreams via magnetic relaxation,” Shirsh Lata Soni, Mojtaba Akhavan-Tafi, Gabriel Ho Hin Suen, Justin Kasper, Marco Velli, Rossana De Marco, Christopher Owen, Astrophysical Journal (2024). DOI: 10.3847/1538-4357/ad94da