Sputnik 1 became the first artificial object to orbit Earth in 1957. The Soviet Union launched the satellite on 4 October 1957 from Baikonur Cosmodrome aboard a modified R-7 ICBM. Its launch opened the Space Age and began the United States–Soviet space race.
Sputnik 1 was a polished metal sphere about 58 centimetres across, with four whip antennas. It transmitted radio beeps that could be received by radio operators around the world. The satellite completed an orbit roughly every 96 minutes, travelling at several kilometres per second.
Sputnik 1 remained in orbit for about three months before atmospheric drag caused it to re-enter on 4 January 1958. It is sometimes confused with Sputnik 2, which carried the dog Laika, or Explorer 1, the first US satellite. Sputnik 1 carried no scientific instruments beyond its radio transmitters, but its measurements helped confirm the density of the upper atmosphere.