A recent study published in 'Science', led by the Smithsonian Astrophysical Observatory (SAO) at the Center for Astrophysics | Harvard and Smithsonian (CfA), provides conclusive evidence that magnetic "switchbacks," or large kinks in the Sun's magnetic field, play a critical role in energizing the fastest solar winds near the Sun.
"Our study addresses a huge open question about how the solar wind is energized and helps us understand how the Sun affects its environment and, ultimately, the Earth," said Yeimy Rivera of the CfA who co-led the study. "If this process happens in our local star, it's highly likely that this powers winds from other stars across the Milky Way galaxy and beyond and could have implications for the habitability of exoplanets."
NASA's Parker Solar Probe had previously observed that these switchbacks were prevalent throughout the solar wind. In 2021, when Parker became the first spacecraft to enter the Sun's magnetic atmosphere, scientists noticed that switchbacks intensified as Parker approached the outer edge of the atmosphere. However, until now, there was no direct evidence linking this phenomenon to the energy required to sustain the solar wind.
"About three years ago, I was giving a talk about how fascinating these waves are," said co-author Mike Stevens, also at the CfA. "At the end, an astronomy professor stood up and said 'that's neat, but do they actually matter?'"
To address this question, scientists utilized data from both Parker and ESA's Solar Orbiter, which is equipped with complementary instruments to measure solar wind at larger distances. A fortuitous alignment in February 2022 allowed both spacecraft to measure the same solar wind stream within two days of each other, providing critical insights.
"We didn't initially realize that Parker and Solar Orbiter were measuring the same thing at all. Parker saw this slower plasma near the Sun that was full of switchback waves, and then Solar Orbiter recorded a fast stream which had received heat and with very little wave activity," said Samuel Badman of the CfA, the other co-lead of the study. "When we connected the two, that was a real eureka moment."
Scientists have long understood that energy is transferred within the Sun's corona and the solar wind through "Alfven waves," which carry energy through plasma, the superheated state of matter comprising most of the Sun. However, it wasn't until these recent missions that the impact of Alfven waves on the solar wind could be measured directly.
The new findings demonstrate that Alfven waves, particularly in the form of switchbacks, deliver sufficient energy to account for the observed heating and acceleration in the faster solar wind stream as it moves away from the Sun. This discovery is a critical step toward improving forecasts of solar activity and understanding how similar processes might occur in other stars.
"It took over half a century to confirm that Alfvenic wave acceleration and heating are important processes, and they happen in approximately the way we think they do," said John Belcher, emeritus professor from the Massachusetts Institute of Technology who was not involved in this study. "This will be a classic paper and it helps fulfill one of the main goals of the Parker Solar Probe."
Research Report:In situ observations of large-amplitude Alfven waves heating and accelerating the solar wind
Related Links
Smithsonian Astrophysical Observatory
Solar Science News at SpaceDaily
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