NASA’s Curiosity Mars rover, recently recovered from an arm injury, is exploring new territory again. This time it is examining a zone of two-tone mineral veins in an area dubbed “Garden City” by NASA researchers. The “ice-cream-sandwich” rocks were formed by liquid, flowing through cracks in existing stone.
According to researchers the liquid which formed the white veins must have flowed after the wet conditions which originally formed the lake bed examined by curiosity at the base of Mount Sharp.
In the last seven months, Curiosity collected three samples by driving lower on the mountain. Each site showed a different mineral composition. The most recent site included cristobalite, a silica mineral. The considerable differences in the samples will provide researchers with a record of the various stages of geological evolution in the region.
The Garden City region is composed of a network of ridges which were made visible by the erosion of surrounding bedrock. Each ridge is approximately 2.5 inches high, 1.25 inches wide and composed of both bright and dark material.
“Some of them look like ice-cream sandwiches: dark on both edges and white in the middle. These materials tell us about secondary fluids that were transported through the region after the host rock formed,” said Linda Kah, a Curiosity science-team member at the University of Tennessee, Knoxville in a statement.
When liquid flows over cracked rock, it leaves mineral traces in the fractures, affecting the chemistry of the surrounding rock. This can tell researchers a great deal about what the liquid was, where it came from and when.
“At least two secondary fluids have left evidence here. We want to understand the chemistry of the different fluids that were here and the sequence of events. How have later fluids affected the host rock?”
NASA researchers know that the bedrock formed from lake-bed mudstones during a warm-wet period on Mars. They also know that the material that makes up the dark lines flowed at an earlier time than the calcium-sulcate-rich white veins.
Garden City is 39 feet higher than the bottom edge of the “Pahrump Hills” outcrop where Curiosity has spent the last six months. During that time it climbed from the lower edge to higher sections three times to examine rock structures and find the best sites to sample.
“We investigated Pahrump Hills the way a field geologist would, looking over the whole outcrop first to choose the best samples to collect, and it paid off,” said David Blake of NASA’s Ames Research Center.
Blake is principal investigator for the Chemistry and Mineralogy (CheMin) analytical laboratory instrument inside the rover.
Analysis of the three Pahrump Hills drilling sites is still preliminary, but each sample shows clear differences in chemical composition.
“Telegraph Peak has almost no evidence of clay minerals, the hematite is nearly gone and jarosite abundance is down. The big thing about this sample is the huge amount of cristobalite, at about 10 percent or more of the crystalline material,” said Blake.
A sample has not yet been taken from the Garden City region.
NASA is likely to be cautious in collecting the next sample after a transient short circuit took the rover out of commission for a few weeks during the last sample collection.
