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Space may not be as silent as we commonly believe. New research has reproduced Earth’s magnetic drumbeat, the sound that Earth’s magnetic shield – the magnetosphere – makes when it is struck by plasma jets from the sun.

Scientists have long been aware of electromagnetic waves travelling around Earth that resonate like string instruments and whistle like wind instruments. That orchestra finally has a beat according to research from Queen Mary University of London published in Nature Communications which has added a percussive member to the cosmic ensemble: a giant drum, triggered by plasma jets striking the boundary of Earth’s protective magnetosphere.

You can listen to the reproduced sound above (Martin Archer, Queen’s University)

The magnetosphere, is encased by a boundary region known as the magnetopause – our first barrier to high-energy particles coming from the Sun. At the magnetopause, the majority of solar particles are deflected around Earth, but under certain conditions some sneak through.

Understanding the mechanics of the magnetopause is key to helping keep our satellites, telecommunications and astronauts safe from the potentially harmful radiation these particles bring.

As an impulse strikes the magnetopause, ripples travel along its surface, these perturbations are then reflected back when they approach the magnetic poles.

The interference of the original and reflected waves leads to a standing wave pattern, in which specific points appear to be standing still while others vibrate back and forth. This is very similar to the way the skin of a drum vibrates when struck.

The effect was predicted 45-years-ago but this research represents the first-time it has been heard.

Dr Martin Archer, a space physicist at Queen Mary University of London and lead author of the paper, said: “There had been speculation that these drum-like vibrations might not occur at all, given the lack of evidence over the 45 years since they were proposed. Another possibility was that they are just very hard to definitively detect.

“Earth’s magnetic shield is continuously buffeted with turbulence so we thought that clear evidence for the proposed booming vibrations might require a single sharp hit from an impulse. You would also need lots of satellites in just the right places during this event so that other known sounds or resonances could be ruled out. The event in the paper ticked all those quite strict boxes and at last we’ve shown the boundary’s natural response.”

The researchers used observations from five NASA THEMIS satellites when they were ideally located as a strong isolated plasma jet slammed into the magnetopause. The probes were able to detect the boundary’s oscillations and the resulting sounds within the Earth’s magnetic shield, which agreed with the theory and gave the researchers the ability to rule out all other possible explanations.

Many impulses which can impact our magnetic shield originate from the solar wind, charged particles in the form of plasma that continually blow off the Sun, or are a result of the complicated interaction of the solar wind with Earth’s magnetic field, as was technically the case for this event.

The interplay of Earth’s magnetic field with the solar wind forms a magnetic shield around the planet, bounded by the magnetopause, which protects us from much of the radiation present in space.

Movements of the magnetopause are important in controlling the flow of energy within our space environment with wide-ranging effects on space weather, which is how phenomena from space can potentially damage technology like power grids, GPS and even passenger airlines.

The discovery that the boundary moves in this way sheds light on potential global consequences that previously had not been considered.

Other planets like Mercury, Jupiter and Saturn also have similar magnetic shields and so the same drum-like vibrations may be possible elsewhere.

Further research is needed to understand how often the vibrations occur at Earth and whether they exist at other planets as well. Their consequences also need further study using satellite and ground-based observations.

Header image: Artist rendition of a plasma jet impact (yellow) generating standing waves at the magnetopause boundary (blue) and in the magnetosphere (green). The outer group of four THEMIS probes witnessed the flapping of the magnetopause over each satellite in succession, confirming the expected behaviour/frequency of the theorised magnetopause eigenmode wave ( E. Masongsong/UCLA, M. Archer/QMUL, H. Hietala/UTU)

Original research: https://www.nature.com/articles/s41467-018-08134-5





















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