NASA scientists celebrate the discovery of nearly conclusive evidence that water once flowed freely on the surface of Mars -- almost certainly a key requirement for any planet to have ever harbored life as we know it. You might wonder: How does the picture above, taken of a rock outcrop called "Link," show evidence of a once-free-flowing stream?
Image Credit: NASA/JPL-Caltech/MSSS
Notice anything similar? The left is a close-up of the Link rock outcrop on Mars; the right is a photo of a known dried streambed on Earth. The smooth, round pebbles cemented together are typical of sedimentary conglomerate structures formed in the beds of streams and creeks.
Image Credit: NASA/JPL-Caltech/MSSS and PSI
This is the Goulburn Scour, which is a patch of ground that has been burned by bursts from Curiosity's engine during the rover's descent. This area, now cleared of dust and loose debris, shows clearly where water once flowed over sandy conglomerate and round pebbles.
Image Credit: NASA/JPL-Caltech/MSSS
Here is another view of the streambed, showing a rock outcrop known as "Hottah." This outcrop reveals some of the same kinds of rounded pebbles loosed from the sedimentary conglomerate. These small, rounded fragments must have been deposited by the flow of water, since they are too large to have been transported by strong winds.
Image Credit: NASA/JPL-Caltech/MSSS
This image shows a closer view of the same outcrop -- "Hottah," which was named after a lake back here on Earth, in Canada. The circled fragment, or "clast," is believed to be much too large to have been transported by wind, meaning it probably got to where it was by being pulled along in a stream that has long-since dried up. Click ahead to see an overhead view of where scientists believe this water used to flow.
Image Credit: NASA/JPL-Caltech/MSSS
This map shows an overhead view of the section of the Gale Crater where water is now believed to have once flowed. This includes an alluvial fan, where particles carried along by the downhill motion of water were deposited as sediment.
Image Credit: NASA/JPL-Caltech/UofA
Here is another false-color view of the sediment-riddled area where an ancient Martian stream once planted pebbles and sand.
Image Credit: NASA/JPL-Caltech/ASU
This overhead map shows where the Curiosity rover has traveled so far, including its scorched touchdown site, as well as the two rocky outcrops that provide the strongest-yet evidence that Mars once hosted free-flowing bodies of water. To the right, you can see Glenelg, which is Curiosity's eventual destination and a site of great interest to scientists here on Earth. What will we learn next about Mars?
Image Credit: NASA/JPL-Caltech/Univ. of Arizona
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