Two-tone discovery yields evidence of Martian water
Vein of minerals reveal signs of past hydration action
Climbing up Mount Sharp in the middle of Gale Crater, NASA’s Mars rover Curiosity has discovered a two-tone vein of minerals that reveal multiple episodes of water flowing through rock — even after the lake that once filled the bottom of the crater had ceased to be.
The rover’s discovery points to an even more complex, and perhaps long-lived, watery environment on the Red Planet.
“Not only does this help us try to understand the chemistry of the rocks that we measure in the region, but on a different sort of scale it tells us that fluids were around on Mars for a long time,” said Linda Kah, a sedimentary geologist at the University of Tennessee Knoxville, and a member of Curiosity’s science team.
The duo-tone deposits, at a spot called Garden City, sit some 39 feet above the lower edge of the Pahrump Hills outcrop, which is part of the basal layer of the 3-milehigh Mount Sharp. They feature both light and dark regions. They rise about 2.5 inches above the surface like ridges, because the rock that surrounded them has worn away. These kinds of veins are formed when fluid flows through cracks in a rock and leaves minerals behind.
Most veins have been bright and light-colored, Kah said, often filled with calcium sulfate. On Earth, such mineral deposits are often associated with salty water. But the dark deposits were somewhat unexpected, she said.
The dark parts often seem to line either side of the white veins, rather like an ice cream sandwich — a description Kah’s 10-year-old son Douglas came up with.
“I think they’re incredibly gorgeous and beautiful,” she said.
Researchers look at Martian rocks in part to see how water (and the stuff in the water) may have affected a particular rock during a particular era. But if the same rock is getting soaked with very different kinds of water sources over time, then it may show a confusing mix of traits from a long period in which the environment dramatically changed over and over again.
That’s why the mineral veins are so helpful. The deposits in the cracks can look very different from the surrounding rock because they were formed much later than the rock itself. So while the rock’s chemistry and mineralogy will have been affected by multiple environments, the mineral vein offers a snapshot of at least one individual era in the Red Planet’s history.
In this case, this mineral vein actually offers snapshots into three environments. At first the scientists thought there were two different epochs, represented by the light and dark deposits, but it turns out that some dark spots are chemically very different from other dark areas.