Two fleeting, Earth-size auroral storms were imaged by the Hubble Space Telescope as they flared up on the dayside of the gas giant in November 2011. (See "Uranus Has a Bright New Spot, Picture Shows.")

"The last time we had any definite signals of auroral activity on Uranus was when NASA's Voyager 2 probe swung by in 1986," said study leader Laurent Lamy, an astronomer at the Observatoire de Paris in Meudon, France.

"But this is the first time we can actually see these emissions light up with an Earth-based telescope."

Auroras are light displays often seen at the highest latitudes of Earth, Jupiter, and Saturn—all of which all have magnetospheres that act as shields against incoming