In what's beginning to look like a case of planetary measles, a third red spot has appeared alongside its cousins ? the Great Red Spot and Red Spot Jr. ? in the turbulent Jovian atmosphere.

This third red spot, which is a fraction of the size of the two other features, lies to the west of the Great Red Spot in the same latitude band of clouds.

The new red spot was previously a white oval-shaped storm. The change to a red colour indicates its swirling storm clouds are rising to heights like the clouds of the Great Red Spot. One possible explanation is that the red storm is so powerful it dredges material from deep beneath Jupiter's cloud tops and lifts it to higher altitudes where solar ultraviolet radiation ? via some unknown chemical reaction ? produces the familiar brick colour.

Credit: NASA, ESA and M. Wong and I. de Pater (University of California, Berkeley)