Two of Jupiter's satellites, Europa and Ganymede, pull Io into an elliptical orbit around Jupiter. Differences in the strength of Jupiter's gravitational pull as the distance between the planet and Io varies causes slight changes in Io's shape. Scientists believe that Io heats up internally when it changes shape.
The Atomic Age, also known as the Atomic Era, is the period of history following the detonation of the first nuclear (atomic) bomb, Trinity, on July 16, 1945 during World War II.
On 6 August 1945, the U.S. Army Air Forces detonated a uranium gun-type fission bomb over the Japanese city of Hiroshima; three days later, on 9 August, the U.S. Army Air Forces detonated a plutonium implosion-type fission bomb codenamed  Fat Man  over the Japanese city of Nagasaki. thermonuclear weapon weighing little more than 2,400 pounds (1,100 kg) can produce an explosive force comparable to the detonation of more than 1.2 million tons (1.1 million tonnes) of TNT. A nuclear device no larger than traditional bombs can devastate an entire city by blast, fire, and radiation.