Growing Evidence of Granite Suggests a More Complex Side of Mars

Growing evidence of granite on Mars' surface suggests a more complex past for the planet than originally imagined by scientists.

Using remote sensing techniques and infrared spectroscopy, researchers were able to peer inside an ancient volcano where they found large amounts of feldspar, a key ingredient of granite.

"We're providing the most compelling evidence to date that Mars has granitic rocks," James Wray, an assistant professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology and the study's lead author, said in a statement.

While most volcanoes on Mars are covered in dust, the one Wray and his team examined is constantly being stripped bare by some of the fastest-moving sand dunes on Mars, making it a perfect place for observation.

"Using the kind of infrared spectroscopic technique we were using, you shouldn't really be able to detect feldspar minerals, unless there's really, really a lot of feldspar and very little of the dark minerals that you get in basalt," Wray said.

Based on the feldspar's location as well as the absence of dark minerals, scientists hypothesize granite may have formed on the Red Planet when magma slowly cooled on its surface, causing low density melt to separate from dense crystals. This process, known as fractionation, when maintained over the course of millennia, gives way to granite.

"We think some of the volcanoes on Mars were sporadically active for billions of years," Wray said. "It seems plausible that in a volcano you could get enough iterations of that reprocessing that you could form something like granite."

The research, published in the journal Nature Geoscience, builds on the rover Curiosity's discovery earlier this year of soils with a similar composition to granite. The findings shocked the scientific world, which had cast Mars as geologically simplistic given the ubiquitousness of basaltic rock found there.

"We talk about water on Mars all the time, but the history of volcanism on Mars is another thing that we'd like to try to understand," Wray said. "What kinds of rocks have been forming over the planet's history? We thought that it was a pretty easy answer, but we're now joining the emerging chorus saying things may be a little bit more diverse on Mars, as they are on Earth."