NASA's Curiosity rover has discovered much higher concentrations of silica at some Martian sites it has investigated in the past seven months than anywhere else it has visited since landing on the Red Planet forty months ago, NASA announced this week.
Silica makes up nine-tenths of the composition of some of the rocks. It is a rock-forming chemical combining the elements silicon and oxygen, commonly seen on Earth as quartz, but also in many other minerals.
According to NASA scientists, water that is acidic would tend to carry other ingredients away and leave silica behind. Alkaline or neutral water could bring in dissolved silica that would be deposited from the solution. The recent findings on Mount Sharp have intriguing threads linked to what an earlier NASA rover, Spirit, found halfway around Mars. There, signs of sulfuric acidity were observed, but Curiosity's science team is still considering both scenarios - and others - to explain the findings on Mount Sharp.
"These high-silica compositions are a puzzle. You can boost the concentration of silica either by leaching away other ingredients while leaving the silica behind, or by bringing in silica from somewhere else," said Albert Yen, a Curiosity science team member at NASA's Jet Propulsion Laboratory, Pasadena, California. "Either of those processes involve water. If we can determine which happened, we'll learn more about other conditions in those ancient wet environments."
Adding to the recent discovery, some silica at one rock Curiosity drilled, called "Buckskin," is in a mineral named tridymite, rare on Earth and never seen before on Mars. The usual origin of tridymite on Earth involves high temperatures in igneous or metamorphic rocks, but the finely layered sedimentary rocks examined by Curiosity have been interpreted as lakebed deposits. Also, tridymite is found in volcanic deposits with high silica content.
Rocks on Mars' surface generally have less silica, like basalts in Hawaii, though some silica-rich (silicic) rocks have been found by Mars rovers and orbiters. Magma, the molten source material of volcanoes, can evolve on Earth to become silicic. Tridymite found at Buckskin may be evidence for magmatic evolution on Mars, scientists say.
"What we're seeing on Mount Sharp is dramatically different from what we saw in the first two years of the mission," said Curiosity Project Scientist Ashwin Vasavada of JPL. "There's so much variability within relatively short distances. The silica is one indicator of how the chemistry changed. It's such a multifaceted and curious discovery, we're going to take a while figuring it out."
ABOVE IMAGE: An annotated composite image with the locations of the "Big Sky" and "Greenhorn" drilling targets and with color-coded indicators of the amount of silica in targets examined by the laser-firing Chemistry and Camera instrument. A key on the right shows the percentage of silica (SiO2), by weight, corresponding to the color-coding. NASA says that the enrichment in silica clearly corresponds to the fracture zones. Credit: NASA/JPL-Caltech/MSSS