Curiosity: the rivers of Mars

NASA has released images returned to Earth by the Curiosity rover of what appears to be an ancient stream bed, together with images showing further evidence of liquid water once having flowed freely within Gale Crater.

The images have been captured at separate locations on the route to Glenelg, with the first images being captured on Sol 27 (September 2nd), with additional images of another location being captured on Sol 39 (September 14th).

The Link outcrop images on Sol 27 using the 100mm Mastcam

The first set of these images were of an outcrop of rock dubbed Link, and showed rounded gravel fragments, called clasts, up to a  few centimetres in size within the rock outcrop. Too large to have been moved as a result of wind action, these clasts have been deemed to be consistent with a sedimentary conglomerate, or a rock that was formed by the deposition of water and is composed of many smaller rounded rocks cemented together.

A close-up of Link (l) compared with similar rocks seen on Earth (r).  Erosion of the outcrop on Mars has resulted in gravel clasts which have fallen onto the ground, creating the gravel pile. The outcrop characteristics are consistent with a sedimentary conglomerate, or a rock that was formed by the deposition of water

On Sol 39, Curiosity imaged a more remarkable outcrop, dubbed Hottah after Hottah Lake in Canada’s Northwest Territories. The exposed bedrock in the images, again captured with the 100mm Mastcam, is made up of smaller fragments cemented together to again form sedimentary conglomerate.

The location of the stream bed lies between the north rim of Gale Crater and the base of “Mount Sharp”, the mound towards the centre of the crater which Curiosity will explore later in the mission. Imaging of the region from orbit shows an alluvial fan of material washed down from the rim, streaked by many apparent channels, sitting uphill of the new finds, further evidence that water was once free-flowing in the region, probably over a reasonably long period of time in Mars’ ancient past. The images of the outcrops themselves show what are referred to as “classic conglomerates”, rocks that are made up of gravels and sand which have been cemented together. The sizes and shapes of stones offer clues to the speed and distance of the ancient stream’s flow.

“From the size of gravels it carried, we can interpret the water was moving about 3 feet [1 metre] per second, with a depth somewhere between ankle and hip deep,” William Deitrich, an MSL science co-investigator said, reviewing the images.

The Hottah outcropping of bedrock – evidence of an ancient stream bed imaged by Curiosity

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