WASHINGTON (Reuters) -- Jupiter's Great Red Spot -- a high-pressure storm on the big planet's surface -- has been around for centuries, but Monday astronomers released images of a new, smaller Jovian storm they call Red Spot Jr.

Using the Keck II telescope on Hawaii's Mauna Kea, scientists from the University of California, Berkeley, and the W.M. Keck Observatory captured a high-resolution picture of both spots on July 20.

Red Spot Jr. is about as wide as Earth's diameter and formed from the merger of three white spots very recently, sometime between 1998 and 2000, and only turned red in December 2005, the astronomers said in a statement.

The Great Red Spot is nearly twice its smaller companion's size and has been circling Jupiter for at least 342 years. But the two are located in the same area and appear to be racing each other around the planet.

The two spots are about the same color when seen in visible light, but Red Spot Jr. was much darker when viewed at infrared wavelengths, the scientists said.

That difference could mean the smaller storm's cloud tops are lower than the big storm's.