Cyclone on Mars

An enormous cyclonic storm system rages in the northern polar regions of the planet Mars in this 1999 Hubble Space Telescope image. Nearly four times the size of the state of Texas, the storm is composed of water ice clouds like storm systems on Earth, rather than dust typically found in Martian storms. The storm is nearly 1,100 miles across in the east-west direction and 900 miles in the north-south direction. The eye of the storm is nearly 200 miles in diameter. The system is larger than the planet's residual north polar ice cap, and is comparable in size to similarly shaped terrestrial hurricanes. The storm consists of at least three, and perhaps more, bands of clouds organized into a spiral structure and wrapped counterclockwise around a hollow central core or "eye." The storm appeared in the middle of the Martian northern hemisphere's summer season, after the planet's seasonal carbon dioxide polar cap has completely sublimated away, leaving only the underlying residual water ice cap. Smaller spiral storms seen previously by NASA's Viking Orbiter were also detected during the northern summer season, and also at high northern latitudes.