What significant physical phenomenon did Explorer I help discover in relation to Earth's outer atmosphere?

Explorer I, the first satellite launched by the United States in 1958, played a crucial role in the discovery of the Van Allen radiation belts. These belts are zones of charged particles, primarily electrons and protons, that are trapped by Earth's magnetic field and exist in the outer atmosphere. The scientific observations made by Explorer I indicated that the intensity of cosmic radiation was much higher than expected at certain altitudes, which led to the conclusion that there were distinct regions around Earth filled with these energetic particles.

The significance of this discovery lies in its implications for both space science and our understanding of the Earth's magnetic field. The Van Allen belts protect the planet from the harmful effects of solar and cosmic radiation, making it critical for life on Earth and important for future space exploration. This knowledge has helped scientists develop better shielding for satellites and astronauts, as well as gain insights into the broader influences of solar activity on Earth's environment.