Image credit: NASA/JPL-Caltech/MSSS and PSI
Rock Outcrops on Mars and Earth: This set of images compares the Link outcrop of rocks on Mars (left) with similar rocks seen on Earth (right). The image of Link, obtained by NASA's Curiosity rover, shows rounded gravel fragments, or clasts, up to a couple inches (few centimeters), 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. A typical Earth example of sedimentary conglomerate formed of gravel fragments in a stream is shown on the right. An annotated version of the image highlights a piece of gravel that is about 0.4 inches (1 centimeter) across. It was selected as an example of coarse size and rounded shape. 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. The name Link is derived from a significant rock formation in the Northwest Territories of Canada, where there is also a lake with the same name. Scientists enhanced the color in the Mars image to show the scene as it would appear under the lighting conditions we have on Earth, which helps in analyzing the terrain. The Link outcrop was imaged with the 100-millimeter Mast Camera on Sept. 2, 2012, which was the 27th sol, or Martian day of operations.
Image credit: NASA/JPL-Caltech/MSSS
Link to a Watery Past: In this image from NASA's Curiosity rover, a rock outcrop called Link pops out from a Martian surface that is elsewhere blanketed by reddish-brown dust. The Link outcrop was imaged with the 100-millimeter Mast Camera on Sept. 2, 2012, which was the 27th sol, or Martian day of operations. The name Link is derived from a significant rock formation in the Northwest Territories of Canada, where there is also a lake with the same name. Scientists enhanced the color in this version to show the Martian scene as it would appear under the lighting conditions we have on Earth, which helps in analyzing the terrain.
Curiosity has seen evidence of an ancient, flowing stream on Mars. The secret is in the Martian gravel.
NASA reports, "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," said Curiosity science co-investigator Rebecca Williams of the Planetary Science Institute in Tucson, Ariz.
The sizes and shapes of the stones cemented into conglomerate rock at the discovery sites offer clues about the speed and distance of the stream. The gravels ranges in size from as small a grain of sand, to as large as a golf ball.
Earlier evidence suggested the presence of water on Mars, but the discovery of "rocks containing ancient streambed gravels -- is the first of its kind," says NASA.
"From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep," said Curiosity science co-investigator William Dietrich of the University of California, Berkeley. "Plenty of papers have been written about channels on Mars with many different hypotheses about the flows in them. This is the first time we're actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it."
Discovery sites "Hottah" and "Link" are located between the north rim of Gale Crater and the base of Mount Sharp. Existing images from the Mars orbiter (MRO) allowed for additional interpretation of the area, showing an "alluvial fan of material washed down from the rim, streaked by many apparent channels, sitting uphill of the new finds," says the space agency.
"Hottah looks like someone jack-hammered up a slab of city sidewalk, but it's really a tilted block of an ancient streambed," said Mars Science Laboratory Project Scientist John Grotzinger of the California Institute of Technology in Pasadena.
The two-year prime mission of the Mars Science Laboratory is to investigate whether areas in Gale Crater ever offered conditions favorable for microbial life. It's believed that clay and sulfate minerals in the slope of Mount Sharp could be preserving "potential ingredients for life," says NASA.
"A long-flowing stream can be a habitable environment," said Grotzinger. "It is not our top choice as an environment for preservation of organics, though. We're still going to Mount Sharp, but this is insurance that we have already found our first potentially habitable environment."