Evidence from the Hubble Space Telescope shows that one of Jupiter’s spots recently changed color and increased in strength, equaling the power of its better-known cousin, the Great Red Spot.

The spots on the gaseous planet are actually powerful storms that have been raging on the surface for hundreds of years. The Great Red Spot alone is three times the size of Earth and has wind speeds of about 400 mph.

Xiaoqing Wu, associate professor of geological and atmospheric sciences, said although the storms on Jupiter have similarities to those on Earth, some of the mechanics of storm formation and propagation are different.

“Storms on Earth need a supply of moisture or they will die out,” Wu said.

He said since Jupiter’s storms are fueled by gases and not water, temperature is probably more of a factor in storm formation.

A little more than a year ago, the Earth-sized Little Red Spot was instead a pale white color. The storm is said to be picking up sulfurous compounds from the planet’s surface that give the spot its new reddish hue.

William Gallus, professor and program director for geological and atmospheric sciences, said as the storm wind speeds grew stronger, more winds traveled upward and into the storm spiral. The upward movement of air then brought more of the color-inducing compounds into the main part of the storm and caused the color change.

Gallus said the gaseous nature of Jupiter allowed the storms to have life spans far longer than an Earth storm. A terrestrial storm weakens as it passes over dry land since it cannot draw moisture to fuel itself, however, a storm on a gas planet will always have more gases to draw up into the spiral.

“Friction is what weakens a storm, and friction is much less without a solid planet,” Gallus said.