Which spacecraft was the first to recognize the Van Allen radiation belts?

The first spacecraft to recognize the Van Allen radiation belts was Explorer I. This mission, launched by the United States on January 31, 1958, played a crucial role in advancing our understanding of Earth's magnetic environment. The satellite was equipped with scientific instruments designed to measure cosmic rays, and it detected a significant increase in radiation at certain altitudes. This finding led to the discovery of the two belts of trapped charged particles surrounding the Earth, now known as the Van Allen belts. The success of Explorer I established the importance of space exploration for understanding not only our own planet but also the broader cosmos, marking a significant milestone in space science.