A surprising mineral in a rock sample discovered by NASA scientists on Mars may alter our understanding of how the Red Planet formed. NASA’s Curiosity rover has discovered an unexpected silica mineral called tridymite in a rock sample at Gale Crater on Mars, a finding that suggests the planet hosted explosive volcanoes during its evolution.

NASA’s Mars Science Laboratory rover, Curiosity, has been exploring sedimentary rocks within Gale Crater since landing in August 2012. In July 2015, on Sol 1060 (the number of Martian days since landing), the rover collected powder drilled from the rock at a location named “Buckskin.” Analyzing data from an X-ray diffraction instrument on the rover that identifies minerals, scientists detected significant amounts of a silica mineral called tridymite.

This detection was a surprise to us because Tridymite is generally associated with silicic volcanism, which is known on Earth but was not thought to be important or even present on Mars, researchers said.

The discovery of tridymite might induce scientists to rethink the volcanic history of Mars, suggesting that the planet once had explosive volcanoes that led to the presence of the mineral.

“On Earth, tridymite is formed at high temperatures in an explosive process called silicic volcanism. Mount St Helens, the active volcano in Washington State, and the Satsuma-Iwojima volcano in Japan are examples of such volcanoes,” said Richard Morris, NASA planetary scientist at Johnson Space Center and lead author of the paper.

Tridymite genesis requires the combination of extremely high temperatures and high silica content in the volcanoes, according to the Morris.

“The discovery of tridymite was completely unexpected. This discovery now begs the question of whether Mars experienced a much more violent and explosive volcanic history during the early evolution of the planet than previously thought,” said Doug Ming, co-author of the paper and chief scientist at the space center.

Meanwhile, the scientists seem certain that the mineral is tridymite since it underwent a chemical analysis and was also X-rayed to confirm its identity.

The rover is currently on its way up a hill called Mount Sharp, as the scientist are willing to see if it will be able to find more samples of tridymite.

The study was published in the Proceedings of the National Academy of Sciences (PNAS). Scientists in the Astromaterials Research and Exploration Science (ARES) Division at NASA’s Johnson Space Center in Houston led the study.