So not only is the presence of tridymite a sure sign that true explosive volcanism has occurred on Mars in the past, but it also suggests that plate tectonics were in fact operating here. However, without any source vent or volcano yet located, researchers are unable to say where it’s come from. The mineral samples found within the Gale Crater were likely carried there by ancient water flows, so it’s likely that the source volcano is a long way away from the site.
This isn’t the first time evidence for explosive volcanic activity has been found on Mars. Just this April, a team working with the Mars Reconnaissance Orbiter (MRO) discovered patches of iron oxides and sulfates on the surface that indicated that there was once explosive magma-ice interactions on the Red Planet.
Although not fully understood, contact between magma and water or ice can sometimes cause massive explosions, but only if they mix in a turbulent fashion. They do not require viscous, silica-rich magma to occur though; as seen at Eyjafjallajokull in Iceland in 2010, very runny, high-temperature basaltic lava emerging from a fissure was mixed with overlying glacial ice, which generated enormous, sustained ash columns.
Gale Crater, where Curiosity is currently exploring. NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS
So in the case of Mars’ magma-ice explosions, no silica-rich magma was required – any magma works here. As for Curiosity’s tridymite, though, geological wisdom suggests that not only is a tall stratovolcano required, but so is a semblance of plate tectonics.
This brings this study to a remarkable conclusion: Either the ancient geological activity of Mars has been severely underestimated, or this particular mineral can be formed in another, as-of-yet unknown way. Let’s hope it’s the former, because if it is, then this little robot has just made a groundbreaking discovery.