When NASA's Voyager 2 spacecraft made its way to outer regions of the solar system in the late 80's, it noticed something odd. Both of the ice giant planets, Uranus and Neptune, lacked what's known as a "dipole magnetic field." This was in stark contrast to our own rocky world, as well as the two gas giants Jupitar and Saturn.
As dense materials near a planet's surface cool, they tend to sink into the planet's interior. On the other hand, hotter materials near the planet's interior will rise. The combination of sinking and rising materials creates convection, leading to the movement and mixing of materials within a planet. And if the interior of a planet is electrically conducting (as in, made of liquid metal or water), the convecting material — often described as a dynamo — will generate a dipole magnetic field. Think of it like a magnet with north and south poles. It is this process which generates Earth's magnetic field — the protective barrier that shields us from charged particles.
