On the surface, Saturn seems calm. But the appearance of the largest and hottest vortex ever seen in the solar system has astronomers thinking that Saturn’s atmosphere has more going on than meets the eye.

The oval-shaped maelstrom was created when two warm spots in Saturn’s roiling cloud deck merged. The subsequent storm was invisible to human eyes but shone brightly in infrared wavelengths. It was accompanied by an unprecedented temperature spike that released tons of energy, equivalent to an enormous planetary belch.

All this action is linked to the “Great Springtime Storm” that raged through Saturn’s northern latitudes over late 2010 and much of 2011. This global storm was the largest recorded tempest since 1903 and grew so large that the storm head traveled all the way around the planet and encountered its own tail. After the most visible effects subsided, scientists considered the storm over.

But since May 2011, researchers have been watching two warm spots in Saturn’s clouds using NASA’s Cassini spacecraft and several Earth-based telescopes. Such spots appear periodically and were expected to cool down after a month. Instead, the hotspots merged and produced a colossal cyclone, briefly exceeding even Jupiter’s famous Great Red Spot in size and brightness.

Temperatures in the storm skyrocketed to 150 degrees Fahrenheit, and a huge amount of ethylene – a colorless and odorless gas not typically seen on Saturn — suddenly appeared. The merging hotspots produced 100 times more ethylene than scientists thought possible on Saturn and no one knows where it came from. An odd soupy mixture of gases was also spotted encircling the vortex.

The bright beacon is now expected to slowly fade away and be gone by 2013, though astronomers wonder if there are further surprises to be had on Saturn. Two papers describing the vortex will appear next month, one in the Astrophysical Journal and another in the journal Icarus.

Video: NASA Goddard Space Flight Center