Probes Reveal Alfvén Waves' Role in Heating and Accelerating Solar Wind

Researchers at the Harvard-Smithsonian Center for Astrophysics in the United States reported in the latest issue of the journal "Science" that data from NASA's Parker Solar Probe and the European Space Agency's Solar Orbiter indicate that when the solar wind leaves the outer atmosphere of the sun, Alfvén waves inject energy into the solar wind. This finding might explain why the solar wind is hotter and faster than expected by solar physicists.

Alfvén waves are oscillations in the plasma magnetic field generated by the sun. The observed Alfvén waves, with significant energy, could potentially account for the long-standing mysteries of the speed and temperature of the solar wind, although direct evidence remains lacking.

In late February 2022, the Parker Probe passed through a region about one-fifth the distance between the sun and Mercury, precisely where Alfvén wave activity occurs. Coincidentally, in less than two days, the Solar Orbiter crossed a similar plasma flow at approximately the orbit of Venus.

The Parker Probe measured the plasma flow speed at about 1.4 million kilometers per hour, while the Solar Orbiter recorded a speed of 1.8 million kilometers per hour. The plasma temperature measured by the Solar Orbiter reached up to 200,000 degrees Celsius, three times higher than theoretical estimates. During this time, the Alfvén waves had dissipated. Researchers calculated that the dissipation of these waves injected enough energy into the solar wind to account for the increased speed and temperature measured by the Solar Orbiter.

However, not all experts are fully convinced that this puzzle has been solved. Some scientists suggest that the research team may not have fully considered the complexity of the solar wind, implying that the two probes may not have captured the same plasma flow.