At the beginning of its fourth year in orbit, NASA’s Mars Global Surveyor spacecraft has snapped a picture-postcard view of three Martian valleys that is now available on the Internet and on NASA Television.
The three major valley systems are located east of the Hellas plains. They are Dao Vallis, Niger Vallis and Harmakhis Vallis.
These valleys are believed by some to have been formed — at least in part — by large outbursts of liquid water some time far back in the Martian past, though there is no way to know exactly how many hundreds of millions or billions of years ago this might have occurred. In each valley, water would have flowed toward the area seen at the bottom of the image.
Although their dimensions vary along their courses, the valleys are all roughly 1 kilometer (0.6 miles) deep and range in width from about 40 kilometers (25 miles) down to about 8 kilometers (5 miles).
