Origin of superfast solar wind found by spacecraft flying close to the Sun

The Parker Solar Probe has flown close enough to the surface of the Sun to detect the fine structure of the solar wind close to where it is generated.

In a paper published today in the journal Nature , a team of researchers including from Imperial College London used data from NASA’s Parker Solar Probe to explain how the solar wind is capable of surpassing speeds of one million miles per hour.

By flying through the atmosphere of our star, Parker Solve Probe is living up to its immense potential and changing our understanding of the Sun. Professor Tim Horbury

They discovered that the energy released from the magnetic field near the Sun’s surface is powerful enough to drive the fast solar wind, which is made up of ionised particles - called plasma - that flow outward from the Sun.

Co-author Professor Tim Horbury , from the Department of Physics at Imperial, said: "This work solves a key part of the puzzle of how the Sun drives the solar wind, which has been the most important outstanding problem in solar physics since the start of the Space Age. By flying through the atmosphere of our star, Parker Solve Probe is living up to its immense potential and changing our understanding of the Sun."

Magnetic mechanism

The solar wind forms a giant magnetic bubble, known as the heliosphere, that protects planets in our solar system from a barrage of high-energy cosmic rays that whip around the galaxy. However, the solar wind also carries plasma and part of the Sun’s magnetic field, which can crash into Earth’s magnetosphere and cause disturbances, including geomagnetic storms that can knock out communications and be deadly to astronauts.

Previous studies suggested that the Sun’s magnetic field was somehow driving the solar wind, but researchers didn’t know the underlying mechanism. To better understand these processes, the team used data from the Parker Solar Probe to analyse the plasma flowing out of the corona - the outermost and hottest layer of the Sun.

In April 2021, Parker became the first spacecraft to enter the Sun’s corona and has been nudging closer ever since. The data in the new paper were taken at a distance of 13 solar radii, or roughly 5.6 million miles from the sun.

With the data, the team were able to provide the first characterisation of the bursts of magnetic energy that occur in coronal holes, which are openings in the Sun’s magnetic field and the source of the solar wind.

This showed that heating and acceleration of the solar wind is driven by magnetic reconnection, which occurs when magnetic fields pointing in opposite directions cross-connect, triggering the release of massive amounts of energy.

Overcoming gravity

The researchers demonstrated that magnetic reconnection between open and closed magnetic fields - known as interchange connection - is a continuous process, rather than a series of isolated events as previously thought. This led them to conclude that the rate of magnetic energy release, which drives the outward jet of heated plasma, was powerful enough to overcome gravity and produce the Sun’s fast wind.

By understanding these smaller releases of energy that are constantly occurring on the Sun, researchers hope to understand - and possibly even predict - the larger and more dangerous eruptions that launch plasma out into space. These solar storms can disrupt electric power grids, interfere with high-frequency radio communications and GPS navigation, and damage space-based technologies. In addition to the implications for Earth, findings from this study can be applied to other areas of astronomy.

Co-lead Professor James Drake , from the University of Maryland, said: "Winds are produced by objects throughout the universe, so understanding what drives the wind from the Sun has broad implications. Winds from stars, for example, play a crucial role in shielding planetary systems from galactic cosmic rays, which can impact habitability."

Based on a press release by the University of Maryland.

’ Interchange reconnection as the source of the fast solar wind within coronal holes ’ by S. D. Bale, J. F. Drake et al. is published in Nature.