On September 21, NASA plunged Galileo into the planet Jupiter, in an effort to make sure that the spacecraft didn't come into contact with Europa. On October 19, a large black spot appeared on Jupiter, and no one knows what caused it. Seemingly unrelated, no?
Well, it turns out that Galileo used Plutonium-238 as a fuel source. Is it possible that this Plutonium from Galileo imploded in the dense Jovian atmosphere and caused a nuclear explosion?
The whole article on this can be read at: http://www.enterprisemission.com/NukingJupiter.html