The Solar Wind

The Sun does not just emit light. It constantly releases a stream of charged particles called the solar wind, traveling at 400 to 800 kilometers per second. This wind extends far past Pluto, creating a vast bubble called the heliosphere that shields the entire solar system from interstellar radiation.

Earth's magnetic field deflects much of the solar wind, funneling particles toward the poles where they collide with atmospheric gases and produce auroras.

That shield matters, but atmospheric survival also depends on gravity, chemistry, volcanic replenishment, and distance from the Sun. Mars lost much of its atmosphere after its dynamo faded, yet the comparison is more complicated than magnetic field alone.