The Earth’s magnetic field is shaped by the complex motion of molten metals in the Earth’s core and by interactions with electric particles coming from the Sun. The boundaries of the field are constantly shifting and researchers have found evidence to suggest that the edge of the magnetosphere can vibrate like a drum.
This idea was first proposed 45 years ago. When the outer boundary of the field, known as the magnetopause, is struck by solar plasma, ripples propagate across the surface. When these vibrations reach the poles they are reflected back. This creates an interference pattern known as a standing wave pattern, just like how a drum’s sound is produced.
As reported in Nature Communications, this is the first time that the effect has been observed and the measurement is consistent with the theory. The cause of the standing wave pattern can either be a powerful hit from the solar wind or more subtle interactions between Earth’s magnetic field and the particles in the solar wind.
“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,” lead author Dr Martin Archer, a space physicist at Queen Mary University of London, said in a statement.
“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 observations were possible thanks to a constellation of five NASA THEMIS satellites. They were in the right place at the right time and saw a strong isolated jet of plasma hitting the magnetopause. They were able to study the effect of this impulse and measure the oscillation within the magnetosphere.
There is still much that we don’t know about this phenomenon. We don’t know how often it occurs or even if planets with strong magnetic fields, such as Jupiter and Saturn, experience similar interactions. Understanding the phenomenon gives us important clues about the development of space weather around our planet, and how to keep our electronics safe.