Sept. 14, 2012
This Sept. 14 image, taken by Curiosity and obtained from NASA, shows a Martian rock outcrop in a photo. The outcrop, named “Hottah,” is believed to be an ancient, flowing stream. According to scientists, the outcrop may look like a broken sidewalk, but this geological feature on Mars is actually exposed bedrock made up of smaller fragments cemented together, or what geologists call a sedimentary conglomerate. Scientists theorize that the bedrock was disrupted in the past, giving it the titled angle, most likely via impacts from meteorites. The key evidence for the ancient stream comes from the size and rounded shape of the gravel in and around the bedrock. Hottah has pieces of gravel embedded in it, called clasts, up to a couple inches in size and located within a matrix of sand-size material. Some of the clasts are round in shape, leading the science team to conclude they were transported by a vigorous flow of water. The grains are too large to have been moved by wind.
NASA/JPL-Caltech/MSSS via AFP/Getty Images