What happens to a cosmic-ray proton flying into the Earth's atmosphere at a speed of about 107 m/s? The magnitude of the Earth's B field is approximately 5 X 10-5 T. The mass m of a proton is approximately 10-27 kg. Consider three cases: The proton enters the Earth's atmosphere parallel to the Bb vector field, perpendicular to the field, and at a 30o angle.