Curiosity finds ancient riverbed on Mars
A shallow river once coursed through a great crater on Mars according to the latest images from the surface that suggest the dusty planet was a more hospitable world in ancient times.
Photographs from Nasa's Curiosity rover revealed clear signs of an ancient waterway winding from the northern edge of the Gale crater towards the base of Mount Sharp, a mountain that rises 3.1 miles (5km) from the crater floor. The dried-up riverbed left a trail of pebbles and sand grains that over time became weathered and locked in rock. Their size and shape point to a river somewhere between ankle and waist deep that flowed through the landscape at a speedy metre a second.
The $2.5bn (£1.6bn) trundling science lab began its mission on Mars after a dramatic arrival last month in which the rover was winched to the surface from a spacecraft hovering overhead on rocket thrusters. Powered by radioactive plutonium and lithium-ion batteries, the rover will spend one Martian year, or 687 Earth days, exploring the Gale crater and its central mountain. For much of the mission, the rover will sample rocks on the gentle flanks of Mount Sharp, following a path worked out from pictures snapped by orbiters overhead.
Curiosity is searching not for signs of life past or present, but for evidence that Mars was once habitable. Scores of earlier missions have found evidence for water. Spacecraft orbiting Mars have beamed back images of ancient lakes and gullies, though none that still flows today. The north and south poles are largely frozen water. The latest pictures are the first to show stones and gravel that have been dragged along the Martian surface by a river in the planet's distance past. Nasa geologists said the rounder shape of some of the pebbles suggested they had travelled long distances from above the crater rim.
The rover took the images with a telephoto camera on its central mast, downhill from a pattern of sediments called an alluvial fan created by several water streams perhaps billions of years ago. The stones vary from angular to smooth and range from golf ball-sized to grains of sand... Read more:
