Earth’s magnetosphere protects the planet from the electrically charged particles pouring from the Sun. However, it is only partially effective. Giant whirlpools of plasma can form along the flanks of our magnetic shield, boring into it. These whirlpools are generated by the solar wind sliding past Earth’s magnetic field in roughly the same way as wind blows across the surface of an ocean.
Thanks to multi-point measurements taken by Cluster, the size of these vortices has been found to be huge: around 40 000 km across, nearly six times Earth’s radius.
Computer simulations show that these whirlpools inject electrified gas into Earth’s magnetic environment by forcing magnetic reconnection to take place. This opens passageways that allow the plasma to cross the usually impenetrable boundary.
This discovery has solved a long-running mystery about how the outer layer of Earth’s magnetosphere can be constantly topped up with electrified gas, when it had been thought that it should be acting as a shield.