Mars Curiosity rover locates ancient stream bed The rounded edges of the pebbles, which were found in an outcrop in the planet's Gale Crater, signify that they must have been carried through water over a long distances. They represent the first evidence of sustained flows of water to be found "on-site" and add further weight to the belief that Mars could once have supported life, researchers said. Curiosity, the £1.6bn robot which landed on the planet last year, discovered the pebbles during its first 100 "sols," or Martian days, the equivalent of about 103 days on Earth. Researchers said the pebbles' grain size and roundness strongly suggest they had been carried by water and deposited more than two billion years ago. When rocks are weathered by wind they become coarse and angular, but when they are carried through water and sand the corners and sides turn smooth and round, they explained. Almost all of the 515 pebbles studied had been cemented together and worn in a flat, round and smooth shape, including light and dark coloured rocks in several shades and colours. Morten Bo Madsen, head of the Mars research group at Copenhagen University, said: "In order to have moved and formed these rounded pebbles, there must have been flowing water with a depth of between 10cm and one metre, and a flow rate of about one metre per second (3.6km/h) - slightly faster than a typical natural Danish stream." The ancient streambed was discovered about a quarter of a mile from the rover's landing site. Pictures were taken by Curiosity and analysed by experts back on Earth. The results were published in the Science journal.