NASA’s Curiosity rover mission has discovered geologic evidence that a deep, fast-flowing stream historically coursed across the surface of Mars, said PSI Senior Scientist Rebecca Williams, a Curiosity mission science co-investigator.
Images by Curiosity’s mast cameras of rocks on two Martian outcrops containing ancient streambed gravels indicate long-distance transport by the vigorous flow of surface water on Mars due to the rounded shape of some of the stones. The materials range in size from a grain of sand to a golf ball.
“The shapes tell you they were transported and the sizes tell you they couldn’t be transported by wind. They were transported by water flow,” Williams said.
The set if images seen above compares the Link outcrop of rocks on Mars (left) with similar rocks seen on Earth (right). The image of Link shows rounded gravel fragments, or clasts, within the rock outcrop. Erosion of the outcrop results in gravel clasts that fall onto the ground, creating the gravel pile at left. The outcrop characteristics are 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.
The image on the right shows a typical Earth example of sedimentary conglomerate formed of gravel fragments in a stream. Rounded grains (of any size) occur by abrasion in sediment transport, by wind or water, when the grains bounce against each other. Gravel fragments are too large to be transported by wind. At this size, scientists know the rounding occurred in water transport in a stream.