Near-Earth space is filled with high-energy radiation propagating in a variety of different directions. When this radiation impacts the Earth's atmosphere we can experience a number of adverse effects, including the depletion of the ozone layer and disruptions to telecommunications and power distribution. The Earth's atmosphere and magnetic core help deflect this radiation, but it is not currently known exactly what percentage of incoming radiation breaches these defenses and is deposited in the atmosphere.

In this work, we use a radiation detector on an Earth-orbiting satellite to determine exactly how much radiation the Earth's atmosphere and magnetic field repels. We find that the amount of radiation repelled depends on the angle at which the radiation approaches the Earth. Only about 5% of radiation that is directed straight at the Earth gets repelled, while up to 60% of incoming radiation at shallower angles is repelled. We then use computer simulations to find that the Earth's atmosphere is responsible for repelling the direct radiation, while the Earth's magnetic field is responsible for repelling the radiation at shallow angles.