© NASA
The planets have aligned for researchers from UC Berkeley - quite literally.

A rare cosmic alignment enabled scientists to observe, for the first time, waves of lava bubbling across a giant molten lake on Jupiter's moon Io.

The researchers, who published their findings in Nature last week, first noticed the lava floes by observing neighboring moon Europa pass in front of Io in March 2015. Icy Europa blocked the light from volcanic Io and reflected on its icy surface the two never-before-seen waves.

UC Berkeley's Katherine de Kleer, the lead author on the paper, told IFLScience that the waves, which had "different velocities and start times," tell scientists that "there's some complex system underneath the volcano."

The swells of overturned lava might explain the periodic brightening of Io's Loki Patera, a bowl-shaped crater that measures about 127 miles across, says a press release from UC Berkeley.

Loki Patera, named for the Norse god Loki, is the most active volcanic site on Io - the most active volcanic object in the solar system.

According to UC Berkeley, earthbound astronomers first observed the dimming and brightening of Io in the 1970s. It wasn't until 1979, when Voyager 1 and 2 spacecraft flew past the moon, that scientists determined volcanic activity to be the source of the periodic illumination.

Still, researchers debate whether the brightening is a result of periodic eruptions or the overturning of lava in Io's giant lake.

"If Loki Patera is a sea of lava," de Kleer told UC Berkeley, "it encompasses an area more than a million times that of a typical lava lake on Earth."