What makes some sandstones so soft you can crumble them with your fingers and others hard enough to make a temple that endures a thousand years? So much depends upon cement.
That’s the name given to the minerals filling the space between the sand grains that bind them together into stone. Clay minerals often make a friable sandstone, much tougher quartz cement shores up sand against the ravages of time. Pressure’s also a factor. After all, it’s the pressure from layer upon layer of rock above that compresses sand and mud into stone in the first place.
On April 29 mission scientists commanded the Mars Curiosity rover to make a “mini-drill” test hole in a slab of sandstone named “Windjana” (after a gorge in Australia) to get answers to those questions.
Sandstones on the Red Planet share a similar range of hard to soft as those on Earth. Softer ones erode faster, harder ones endure. Taken together, they shape the wonderfully alien yet oddly familiar landscape inside Gale Crater.
“All of these traits reinforce our interest in drilling here in order understand the chemistry of the fluids that bound these grains together to form the rock,” said Curiosity science team member Melissa Rice of the California Institute of Technology, Pasadena.
After using its brush to whisk red Martian dust from the target rock, Curiosity bored a shallow hole so the rover team could evaluate the interaction between the drill and the rock and view its interior and tailings.
Soon, the team will use the hammering drill – a spinning chisel with a hammer-like motion that breaks rock into powdery bits - to bore up to 2.5 inches (6.4 cm) deep. The fine, gray tailings that pile up around the hole will then be delivered to instruments inside the rover for analysis.
Curiosity last drilled in early Feb. 2013 in Yellowknife Bay, discovering mudstones, rock made of very fine clay deposited as minute grains after being washed downslope from the interior mountains of Gale Crater. The weight overlying rock layers compressed them into layers of sedimentary rock of varying degrees of hardness. While the minerals comprising the mudstones date to between 3.86 and 4.56 billion years old, the area was only exposed to view (and sampling) 80 million years ago through wind erosion.
All of this whets our appetite for what Windjana will reveal about Mars’ climate history.