ESA's Solar Orbiter spacecraft, working in conjunction with NASA's Parker Solar Probe, has made a significant breakthrough in understanding the source of energy that powers the acceleration and heating of the solar wind. By analyzing data from both spacecraft, scientists have discovered that large-scale fluctuations in the Sun's magnetic field, known as Alfvén waves, are responsible for providing the necessary energy.

The solar wind is a continuous stream of charged particles that emanates from the Sun's corona and extends far into space. It is the interaction between the solar wind and Earth's atmosphere that generates the spectacular auroras. However, scientists have long been puzzled by the fact that the solar wind speeds up as it moves away from the Sun, even though it initially exits the corona with lower velocities.

By studying the data from Solar Orbiter and Parker Solar Probe, researchers have now confirmed that Alfvén waves, generated by the Sun's magnetic field, play a crucial role in accelerating the solar wind. Unlike in ordinary gases, such as Earth's atmosphere, where only sound waves can be transmitted, a plasma state like the Sun's atmosphere enables the formation of Alfvén waves, which store and efficiently carry energy through the plasma.

Both Solar Orbiter and Parker Solar Probe are equipped with instruments capable of measuring the properties of the plasma, including its magnetic field. In a fortuitous alignment, the two spacecraft coincidentally passed through the same stream of solar wind in February 2022, albeit at different distances from the Sun.

Taking advantage of this rare opportunity, scientists compared the measurements of the same plasma stream taken by both spacecraft. By analyzing the energy quantities, including the measurement of the stored energy in the magnetic field, known as the wave energy flux, they found that the inclusion of the magnetic energy term was necessary to account for the energy observed at Solar Orbiter.

The research team observed that approximately 10% of the total energy near the Sun, as measured by Parker Solar Probe, was stored in the magnetic field. At a greater distance from the Sun, as measured by Solar Orbiter, this percentage dropped to just 1%. However, the plasma at this location had accelerated and cooled more slowly than expected. This led the team to conclude that the missing magnetic energy was responsible for the acceleration and the slower cooling of the plasma, providing its own heating.

The study also shed light on the importance of magnetic configurations known as switchbacks in the acceleration of the solar wind. These switchbacks, which are large deflections in the Sun's magnetic field lines, were first detected in the 1970s, and their discovery rate has increased significantly with the recent observations by Parker Solar Probe. The team found that these patches of switchbacks contain enough energy to account for the missing portion of the solar wind's acceleration and heating.

The findings of this study not only contribute to our understanding of our own Solar System but also hold implications for other stars in the universe. While the Sun is the only star where we can directly measure the solar wind, the insights gained from this research could potentially apply to other Sun-type stars and those with similar wind processes.

The team is now expanding their analysis to study the slower forms of the solar wind to determine if the Sun's magnetic field energy is involved in their acceleration and heating as well. The collaboration between Solar Orbiter, Parker Solar Probe, and other missions continues to reveal the intricate workings of the Sun's magnetic environment.

The study, titled 'In situ observations of large amplitude Alfvén waves heating and accelerating the solar wind,' has been published in the journal Science. The Solar Orbiter mission, a joint project between ESA and NASA, aims to unravel the mysteries of the Sun and its influence on the solar system.

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