The Curiosity rover has been doing some drilling on Mars, and what is has discovered has NASA scratching their heads. A mineral known as tridymite has been uncovered beneath the surface of Mars. And its presence raises far more questions than it answers.

Tridymite is a silicon dioxide (silica) mineral that crystallizes at low pressure and high temperatures around 800 degrees Celsius (1,472 degrees Fahrenheit). These sorts of conditions can only occur in silicic volcanism: volcanoes with magma which contain a large amount of silica. This is commonplace on Earth due to plate tectonics and flowing water. But Mars lacks of both of those things, begging the question: where did all this tridymite come from?

To answer that, NASA has been looking at terrestrial processes that might provide an alternative way of creating the mineral. So far, they haven’t been able to find any alternative. The hunt for a lower temperature process that can produce tridymite is still on, but as time passes NASA is looking ever more at the alternative. That maybe Mars was a lot more active in the past than we realized.

For tridymite to be created in the only ways we understand to be possible, Mars would have had to have active volcanoes, and for that it would have needed a lot of running water. We know that Mars does in fact contain water, but it would need more than we’d ever expected for these processes to be possible.

But does that mean Mars was once far more Earth-like? Or could there have been another low pressure high temperature process going on with similar results? It’s likely Curiosity alone won’t be able to figure it out – we may need another rover with more specialized equipment to suss this one out.