Researchers using NASA and ESA spacecraft have discovered how magnetic reversals near the Sun excite the solar wind, impacting Earth and potentially affecting the habitability of exoplanets. This breakthrough helps answer long-standing questions about the dynamics of the solar wind and has broader implications for understanding stellar events in the galaxy.

Secrets of the solar wind

Since the 1960s, astronomers have pondered how the Sun’s supersonic “solar wind” (the stream of energetic particles flowing into the Solar System) continues to gain energy after leaving the Sun. Now, a successful combination of two spacecraft, one from NASA and the other from a joint ESA/NASA mission, may have found the answer. The discovery offers important information that could help scientists improve estimates of solar activity affecting the space between the Sun and Earth.

Discovering the power of magnetic switches

In an article recently published in the journal ScienceResearchers present compelling evidence that the fastest solar winds are powered by magnetic “switches” – large kinks in the Sun’s magnetic field.

“Our research addresses a large open question about how the solar wind obtains its energy and helps us understand how the Sun affects the environment and ultimately the Earth,” said Jaimie Rivera, co-lead author of the study and a postdoctoral researcher at the Smithsonian Institution. . The Astrophysical Observatory is part of the Center for Astrophysics at Harvard and Smithsonian University. “If this process occurs in our local star, it is very likely to fuel winds from other stars in the Milky Way galaxy and beyond, and this could have implications for the habitability of exoplanets.”

Value of solar wind energy transfer

Previously, NASA’s Parker Solar Probe had found these switches to be common in the solar wind. Parker, the first spacecraft to enter the Sun’s magnetic atmosphere in 2021, allowed scientists to detect that reversals become sharper and stronger closer to the Sun. But until now, scientists lacked experimental evidence that this intriguing phenomenon actually stores enough energy to be important for the solar wind.

“About three years ago, I talked about how exciting these waves were,” said co-author Mike Stevens, an astrophysicist at the Center for Astrophysics. “Finally the astronomy professor stood up and said: ‘That’s nice, but are these really important?’

Decisive discoveries of dual spaceships

To answer this question, the team of scientists had to use two different spacecraft. Parker is designed to fly through the Sun’s atmosphere, or “corona.” ESA and NASA’s Solar Orbiter mission also orbits relatively close to the Sun and measures the solar wind over long distances.

The discovery was made possible by a chance alignment in February 2022 that allowed both Parker Solar Probe and Solar Orbiter to measure the same solar wind flux two days apart. Solar Orbiter was nearly halfway to the Sun, and Parker was passing at the edge of the Sun’s magnetic atmosphere.

“At first we didn’t realize that Parker and Solar Orbiter were actually measuring the same thing. Parker saw this slower plasma near the Sun that was full of backward waves, and then Solar Orbiter captured a fast stream that was heating up and had very little wave activity.” ” lead author of the study. “When we put the two together, it was a real turning point moment.”

Interaction of Alfvén waves and solar wind

Scientists have long known that energy moves through the Sun’s corona and solar wind, at least in part, via so-called “Alfvén waves.” These waves carry energy through plasma, the superheated state of matter that makes up the solar wind.

But it wasn’t possible to measure how much Alfvén waves had evolved and interacted with the solar wind between the Sun and Earth until two missions were sent ever closer to the Sun at the same time. Scientists can now directly determine how much energy is stored in the magnetic and velocity fluctuations of these waves close to the corona, and how little energy the waves farther from the Sun carry.

A new study shows that key-shaped Alfvén waves provide enough energy to account for the heating and acceleration documented in the faster flow of the solar wind as it moves away from the Sun.

“It has taken more than half a century to confirm that Alfvén wave acceleration and heating are important processes and that they occur largely in the way we thought they did,” said MIT professor emeritus John Belcher, one of the discoverers of Alfvén waves. was in solar wind but was not involved in this study.

Results of new solar wind research

In addition to helping scientists better predict solar activity and space weather, this information also helps us understand mysteries elsewhere in the universe and how sun-like stars and stellar winds work everywhere.

“This discovery is one of the key pieces of the puzzle that answers the 50-year-old question of how the solar wind is accelerated and heated in the deepest parts of the heliosphere, and brings us closer to one of the fundamental scientific goals of the universe.” to work. Parker Solar Probe mission,” said Adam Szabo, Parker Solar Probe mission scientist at NASA.