Our Sun is constantly bombarding us with charged particles. These charged particles form the stellar wind and are ejected from stars across our cosmos. But, luckily for us, the Earth has some defence mechanisms to protect us from these energetic particles. Our home planet has its own magnetic field. Its shape is similar to that of a bar magnet but much larger.
You probably remember the day at school where you placed a bar magnet under a piece of paper and then sprinkled iron fillings on top of it to reveal the magnetic field lines. The magnetic field is a result of electric currents in the Earth’s molten metallic core. On a more familiar scale, all electrical wires that have a current through them have a magnetic field around them. In essence, moving charges produce magnetic fields and magnetic fields move charges.
When the charged particles ejected from the Sun get close to the Earth they begin to get influenced by the magnetic field. The charged particles then start to spiral along the field lines, and then hit our atmosphere at the poles. These particles then excite the molecules in our atmosphere and give off the energy in the form of a beautiful light show, commonly known as the Northern or Southern Lights. On top of this, the charged particles in the stellar wind also carry a magnetic field with them. When this magnetic field interacts with the Earth’s magnetic field, it can cause a huge disruption. Satellites can be affected causing disruption to our navigation and can also disturb our power grids.
A team of scientists at Imperial College London that work on the MAGPIE machine wanted to find out more about these magnetic flows. They did so by carrying out experiments in the laboratory to recreate these conditions. MAGPIE is a machine that can generate one million amps and is discharged through wires as thin as your hair over hundreds of a billionth of a second. The wires basically explode at this point, and produce plumes of charged particles that are travelling at speeds faster than the speed of sound.
These particles are then allowed to flow round different obstacles in order to find out more about the astrophysical scenario in question. All of this cool stuff happens in the basement of Imperial College London in the heart of South Kensington, where the machine spans over two floors. It is an impressive machine which I have had the pleasure of working with on my masters. You can find out more about MAGPIE in one of my previous articles here.
The team was looking specifically at the interaction of the stellar wind with a planet’s magnetic field . When this happens, a region of very hot and dense ‘stuff’ is formed which is known as the magnetopause. This is also grouped with a region of low pressure just behind it. By placing an obstacle in the flow of charged particles produced in MAGPIE, the team were able to display a detached boundary which is analogous to the magnetopause. These incredible results can be extended to the scale of our solar system to model the interaction of the stellar wind with planets like our own. These results were presented last week at the 60th Annual Meeting of the APS Division of Plasma Physics last week in Portland, Oregon.