london

Credit: JIM BELL/STEVE LEE/MIKE WOLFF/NASA

A giant cyclonic storm was seen raging in the northern polar regions of Mars last month by the Hubble Space Telescope. The storm, which was 900 miles long and 1,100 miles wide, is the largest ever detected on the planet. It was largely dust-free, and is believed to have been composed of clouds of water ice, similar to storm systems on Earth. The eye of the storm was 200 miles across.

The storm can be seen to the left of the polar ice cap in the picture. The dark spot above the cloud is the extinct volcano Ascraeus Mons, which is 16 miles high and 250 miles across. The storm, detected by Hubble's Wide Field Planetary Camera, has not been seen since and may be over.