May 19, 1999: Astronomers using the Hubble telescope have discovered an enormous cyclonic storm system raging in the northern polar regions of the planet Mars. 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 system is similar to so-called "spiral" storms observed more than 20 years ago by NASA's Viking Orbiter spacecraft, but it is nearly three times as gigantic as the largest previously detected Martian spiral storm system. 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. Each of these pictures illustrates the breadth of this immense storm.See the rest:
Credit: Jim Bell (Cornell U.), Steve Lee (U. Colorado), Mike Wolff (SSI), and NASA