Artist depiction of the solar wind (yellow, left) interacting with Earth’s magnetosphere (blue right). At this interface, large plasma waves can form (inset at left), generating ion beams (yellow arrows) that in turn cause plasma heating to form ion acoustic waves (red). Credit: X. An, E. Masongsong, UCLA EPSS By Emmanuel Masongsong
Waves are a common means of transferring energy from one area or system to another. In space, waves occur in plasmas – very sparse collection of atomic particles – where vibrations can travel through the plasmas’ magnetic fields. Now, Scientists have discovered a new way for different types of waves in space to work together, to heat and accelerate particles in the solar wind.
Using NASA’s Magnetospheric Multiscale spacecraft and computer simulations, UCLA researchers found that large-scale magnetic waves (~2000km), known as Alfvén waves, can generate smaller-scale sound-like waves (50-1500m) that heat particles to high temperatures. This process occurs near boundaries in space where different plasma environments meet, such as at Earth’s magnetopause – the outer edge of our planet’s magnetic shield. The research is published in the latest issue of Physical Review Letters.
This finding solves a long-standing puzzle about how energy moves between different scales in space plasmas and how particles are heated in these environments. It’s similar to how ocean waves can create smaller ripples that eventually break and heat the water. The discovery helps explain how streaming particles from the Sun- the solar wind- are heated as they travel through space. This process of energy transfer can occur at other astrophysical settings, from the Sun’s atmosphere to fusion devices on Earth. This improved understanding could help scientists better predict space weather and advance the development of fusion energy.
The new study uses detailed spacecraft observations to reveal that a large wave’s motion can speed up another smaller, separate type of wave, analogous to laboratory plasma experiments on Earth. However the scale of these wave-heating effects in lab experiments is far too small and rapid to study with terrestrial technology. In contrast, the enormous size of plasma waves in the Earth’s magnetic field magnifies this same effect such that it can be directly observed by dedicated satellites, making it possible to see these processes in real time as reported in the study.
“Fleets of spacecraft are needed to sample the fabric of space itself: plasmas that make up our sun, and the vast majority of the universe,” said lead author Xin An, a researcher in the Earth, Planetary, and Space Sciences department. It is important to investigate the nature of these particles, since plasma wave heating can impact our satellite technology and astronauts, who are especially more vulnerable on the moon, outside of our planet’s protective magnetic bubble.
X. An, et al., “Cross-scale energy transfer from fluid-scale Alfvén waves to kinetic-scale ion acoustic waves in the Earth’s magnetopause boundary layer,” Phys. Rev. Lett. (2024), 133, 225201, doi: https://doi.org/10.1103/PhysRevLett.133.225201. Published 25 November, 2024