School of Physics and Astronomy

Spacecraft measurements reveal mechanism of solar wind heating

A researcher from the School of Physics and Astronomy has led a study which describes the first direct measurement of how energy is transferred from the chaotic electromagnetic fields in space to the particles that make up the solar wind, leading to the heating of interplanetary space.

14 February 2019

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Illustration of the MMS spacecraft measuring the solar wind plasma in the interaction region with the Earth’s magnetic field. Credit: NASA.

A researcher in the Astronomy Unit at Queen Mary University of London has led a study that reveals the mechanism of solar wind heating.

The study, published in Nature Communications and carried out with University of Arizona and the University of Iowa, shows that a process known as Landau damping is responsible for transferring energy from the electromagnetic plasma turbulence in space to electrons in the solar wind causing their energisation.

This process, named after the Nobel-prize winning physicist Lev Landau (1908-1968), occurs when a wave travels through a plasma and the plasma particles that are travelling at a similar speed absorb this energy, leading to a reduction of energy (damping) of the wave.

All across the universe, matter is in an energised plasma state at far higher temperatures than expected. For example, the solar corona is hundreds of times hotter than the surface of the Sun, a mystery which scientists are still trying to understand.

Being able to make direct measurements of the plasma energisation mechanisms in action in the solar wind (as shown in this paper for the first time) will help scientists to understand numerous open questions about the universe.

The researchers discovered this using new high-resolution measurements from NASA's Magnetospheric Multi-Scale (MMS) spacecraft (recently launched in 2015), together with a newly-developed data analysis technique (the field-particle correlation technique).

Lead author Dr Christopher Chen said: “In this study, we made the first direct measurement of the processes involved in turbulent heating in a naturally occurring astrophysical plasma. We also verified the new analysis technique as a tool that can be used to probe plasma energisation and that can be used in a range of follow-up studies on different aspects of plasma behaviour.”

This paper also paves the way for the technique to be used on future missions to other areas of the solar system, such as the NASA Parker Solar Probe (launched in 2018) which is beginning to explore the solar corona and plasma environment near the Sun for the first time.