The drum around the Earth

Why is our planet like a drum?
19 February 2019

Interview with 

Martin Archer, Queen Mary University London


The magnetosphere is a protective layer that surrounds the planet. It's formed by charged particles rushing in from the Sun and interacting with our magnetic field. Forty-five years ago a theory was set out suggesting that when it’s hit by a surge of radiation from the Sun, the whole magnetosphere shakes, like the surface of a drum. This, the theory says, produces electromagnetic radiation that can have consequences for systems on Earth, including our technology. This week scientists proved it really does happen. Adam Murphy has the story…


Adam - The sound you just heard is streams of charged particles travelling at 400 kilometres per second from the Sun hitting our magnetosphere. The magnetosphere is a layer around the planet formed when particles from the Sun meet our magnetic field. It helps to protect our planet and our technology from the harshest effects of these solar streams. And just like striking a drum, when streams from the sun hit this magnetosphere they make ripples in it. Martin Archer is a planetary physicist from Queen Mary University London who's been looking into a 45 year old theory about the Earth's largest drum.

Martin - What we found is some of those ripples which will head towards the northern and southern Poles will get reflected back and you'll end up getting a pattern called a standing wave that's very much like how you get patterns on the surface of a drum and which gives them their notes. So that's what we found about the magnetosphere in this particular study.

Adam - A standing wave is a wave that looks like it's standing still; like a guitar string, or in this case a drum.

Martin - The way that we drew this picture together was by using five different satellites from NASA's THEMIS mission that happened to be in the right place at the right time and essentially allowed us to see the thing hit the Earth's magnetosphere, see the boundary move in response and hear the sounds within our magnetic environment that were caused by it. So it was piecing together those observations that allowed us to finally make this discovery.

Adam - But since particles from the sun are always hitting the Earth how do you isolate one single solar slam.

Martin - It's a complicated problem being able to show direct causality from one thing to another, often because you've got lots of things happening at the same time, all at once. Lots of different processes that can lead to something quite complicated. So that's why we've picked a very specific sort of impulse it was a very strong jet of plasma hitting into our magnetosphere with nothing really very much either side of it happening. So that means we could be very clear about that it was definitely this and not something else going on that was that was causing the effects that we saw.

Adam - And understanding this, it isn't just pie in the sky stuff.

Martin - So the consequences of this are things that we still need to do a bit more work into. But we certainly know that these standing waves do penetrate within to our magnetosphere quite deeply and they're a source of ultra low frequency waves.

Adam - So when these streams from the sun hit the magnetosphere they cause all the charged particles there to wiggle which creates these waves in the magnetosphere itself. And these helped create ultra low frequency waves which may have profound effects on our technology.

Martin - They can accelerate electrons in the radiation belts up to energies that can damage satellites for instance, and there are ideas as well that these waves might affect the Aurora and they can actually heat the top of the atmosphere. So there's lots of different ways in which they could have consequences mainly on our technology. But as I say because we've only just discovered these in the observations now, we've got a long road ahead of us to do further research into really understanding the actual implications.


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