When NASA's Cassini spacecraft was on its way to Saturn in the late 1990s it swung by Earth for a gravitational assist. From a distance of 55,000 miles above the Earth's surface, the probe detected the radio wave bursts that are a signal of terrestrial lightning. (A lightning bolt emits electromagnetic radiation at a variety of wavelengths, including visible light and radio waves.) As Cassini continued to head toward Saturn in the early 2000s, the spacecraft's controllers got a shock. From 100 million miles away, the probe detected radio pulses indicating powerful lightning storms of Saturn. The radio signal was about a million times more powerful than the one it received from Earth.

For years the Saturnian superbolts weren't seen directly, but the radio busts indicated that they occur in a region called Storm Alley in the planet's southern hemisphere. This image shows one bright tempest in that area, the so-called Dragon Storm. Finally, this spring, Cassini captured the first images of lightning flashes on Saturn.