Explorer 1, launched January 31, 1958, by the U.S. Army, was the first United States satellite launched into orbit. This 31-pound (14.06-kilogram) satellite carried instrumentation that led to the discovery of Earth’s radiation belts, which would be named after University of Iowa scientist James A. Van Allen. It followed four months after the launching of the world’s first satellite, the Soviet Union’s Sputnik 1. On October 3, 1957, the Soviet Union placed the large 184-pound (83.5-kilogram) satellite into low Earth orbit. It carried instrumentation to study the density and temperature of the upper atmosphere, and its launch was the event that opened the space age.