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| Striations exposed on the surface between Martian sand dunes (one pictured at top) in Lucaya Crater indicate fluctuating levels of salty groundwater. At “a” we see possible cross beds which are tilted layers of sand within larger layers deposited by wind or water. At b, dark and light strata are similar to that exposed in the dune at top and resemble the striations seen in the Namib Desert on Earth. The photo was taken by NASA’s Mars Reconnaissance Orbiter in infrared, red and blue light. Credit: NASA/JPL-Caltech |
Article Updated: 18 Feb , 2017 - by Bob King
Researcher Dr. Mary Bourke from Trinity College Dublin have discovered a patch of land in an ancient valley in Mars’ Lucaya Crater that appears to have held water in the not-too-distant past, making it a prime target to search for past life forms on the Red Planet. Signs of water past and present pop up everywhere on Mars from now-dry, wriggly riverbeds snaking across arid plains to water ice exposed at the poles during the Martian summer.
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| A valley lined with sand dunes crosses the southern floor of the 21-mile-wide Lucaya Crater, located at latitude 11° south and longitude 52° east on Mars. Striations found between the dunes may have been created by recent water flows. The box shows the area pictured in the close up above. The 3.7-mile-long valley measures between 2,000 and 2,600 feet wide. Credit: NASA/JPL-Caltech with additions by the author |
On Earth, Bourke had done previous studies of dunes in the Namib Desert near Walvis Bay, Namibia and noted “arctuate striations” — crusty arcs of sand cemented by water and minerals — on the surfaces of migrating sand dunes using photos taken by satellite. She subsequently assembled a team to check them out on the ground and discovered that the striations resulted when dune materials had been chemically cemented by salts left behind by evaporating groundwater.
“On Earth, desert dune fields are periodically flooded by water in areas of fluctuating groundwater, and where lakes, rivers and coasts are found in proximity,” said Bourke. These periodic floods leave tell-tale patterns behind them.” Once the material had been cemented, it hardens and remains behind as the dunes continue to migrate downwind.
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| Compare these cemented arctuate striations between dunes near Walvis Bay, Namibia with those in Lucaya Crater’s valley in the earlier image. White arrows highlight particularly prominent examples. Photos in (b) and (c) were taken from the ground. The excavated pit in (c) shows that the dipping sediment layers below the surface match the protruding layers on the surface. Alternating light and dark layers have different salt composition and grain size. Credit: Google Earth (left) and Dr Mary Bourke, Trinity College Dublin |
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