The first surface science results from the Mars Science Laboratory (MSL) mission have provided the most definitive evidence yet of an ancient stream flow on Mars. "This is the first confirmation of sedimentary conglomerates on another planet," said Planetary Science Institute Senior Scientist Rebecca M.E. Williams, lead author of the report.

The size, shape and arrangement of the pebbles embedded in these conglomerate rocks - from the size of sand particles to the size of golf balls - have telltale signs of water transport.

The smooth, rounded shape of the pebbles occurs through multiple collisions within the stream. In addition, many of the pebbles are touching each other, a clear indication that pebbles rolled along the bed of a stream.

PSI Senior Scientist R. Aileen Yingst, a co-author on the paper, documented the roundness of the pebbles and demonstrated that these pebbles are significantly rounder than rocks of this size previously observed on Mars.

"The rounded pebble shape requires significant fluvial abrasion and indicates long-distance water transport of the pebbles, over at least several kilometers" Williams said. "Climate conditions on Mars once enabled the sustained flow of liquid water at the Martian surface. "

Three pavement-like rocks examined with the telephoto capability of MSL rover Curiosity's Mast Camera during the rover's first 40 days on Mars are the basis for the paper. Researchers also used the rover's laser-shooting Chemistry and Camera (ChemCam) instrument to investigate the material.

"Sedimentary conglomerates are a common rock type here on Earth, and now we have found them on Mars. Geologists understand how to use the clues contained in streambed deposits to estimate former flow conditions, and we can apply this knowledge to determine the flow depth and speed on Mars," Williams said.

"The stream was flowing at a minimum speed equivalent to a walking pace - a meter per second - and it was ankle deep to hip deep."

PSI Senior Scientist David T. Vaniman is a member of the ChemCam team, which provided chemical data on the composition of pebbles within the conglomerate. Science paper "Martian Fluvial Conglomerates at Gale Crater"