Sputnik 1 was the space mission that first placed an artificial satellite into Earth orbit.
The Soviet Union launched Sputnik 1 on 4 October 1957 from Baikonur Cosmodrome. The small polished sphere carried four whip antennas and transmitted simple radio signals that could be detected around the world. Its successful launch marked the beginning of the Space Age.
Sputnik 1 orbited Earth every 96.2 minutes at first. It remained in orbit for about three months before re-entering the atmosphere on 4 January 1958. The satellite carried no scientific instruments beyond its radio and monitoring systems, but its measurements provided information about the density of the upper atmosphere.
The launch shocked the United States and intensified the Cold War space competition. The United States answered with Explorer 1 in January 1958, its first satellite, which discovered the Van Allen radiation belts.