Alfvén surface

An alfvén surface is like a protective layer around a planet or star. It's made up of electric and magnetic fields, almost like a bubble. Just like how a bubble can keep things out or in, the alfvén surface helps keep electrically charged particles out of the planet or star. This is really important because too many charged particles can be dangerous and even cause damage. The alfvén surface is named after a scientist named Hannes Alfvén who studied these things.