Initial data from the Parker Solar Probe mission, published in four Nature papers this week, offer new insights into the origins of solar wind and the physics of high-energy particles. The Parker Solar Probe has reached beyond the inner heliosphere of our Solar System to around 24 million kilometres from the Sun, and its on-board instruments have made measurements of events in the corona (the outer atmosphere of the Sun).
The corona produces solar wind, energetic particles that constantly stream away from the Sun. Remote observations have uncovered the details of some mechanisms that underlie the creation of solar winds, but other processes have been harder to explore. Most measurements have been made at a distance of 1 astronomical unit, which is the distance from Earth to the Sun; it is known that solar wind is modified during its passage from the Sun to Earth, but the extent and origin of these changes have been unclear.
The Parker Solar Probe now provides the closest view of the corona so far, providing observations of the Sun that have not previously been possible. For example, previous missions have shown that solar wind is accelerated as it leaves the corona, but it has not been clear how this happens. In one of the new papers, Justin Kasper and colleagues report that changes in the magnetic fields increase the speed of the solar wind flowing away from the Sun. Their measurements record speeds that are higher than those predicted by modelling studies. Another paper, by Stuart Bale and colleagues, focusses on the so-called slow wind (less than 500 kilometres per second), the origins of which have been less clear than that of fast wind. They find that slow wind originates in holes in the corona found near the equator.
Over the next five years the Parker Solar Probe will continue to make new discoveries as it moves closer to the Sun, eventually reaching just over six million kilometres from its surface. During this time the Sun will enter a more active phase of its eleven-year cycle, so we can expect even more exciting results in the coming years, notes Daniel Verscharen in an accompanying News & Views article.
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