Pulsating aurora mysteries uncovered with help from NASA's THEMIS mission

Earth's magnetic bubble -- the magnetosphere -- protects the planet from high-energy radiation coming from the Sun and interstellar space, but during particularly strong solar events, particles can slip through. Once inside, the particles and the energy they carry are stored on the nightside of the magnetosphere, until an event, known as a substorm, releases the energy. The electrons are then sent speeding down into Earth's upper atmosphere where they collide with the other particles and produce the characteristic glow.

Pulsating auroras, however, have a slightly different cause. The magnetosphere is home to a type of plasma wave known as whistler mode chorus. These waves have characteristic rising tones -- reminiscent of the sounds of chirping birds -- and are able to efficiently disturb the electrons. When these waves make their appearance within the magnetosphere, some of the electrons scattered by the wave careen down into Earth's atmosphere, causing the pulsating auroras.

While scientists have long believed this mechanism to be responsible for pulsating auroras, they had no definitive proof until now. The multipoint observations from the ERG satellite and ground-based all-sky cameras from the THEMIS mission allowed scientists to pinpoint the cause and effect, seeing the event from start to end. The results were published in the journal Nature.

Research done with NASA's ground-based camera and Japan's spacecraft in the near-Earth laboratory has applications further afield. Chorus waves have been observed around other planets in the solar system, including Jupiter and Saturn. Likely, the processes observed around Earth can help explain auroral features on these gas giants as well as on planets around other stars. The results also help scientists better understand how plasma waves can influence electrons -- something that occurs in processes across the universe.