What's Carving Active Gullies on Mars? It's Not Water

There's a beautiful, humbling irony in planetary science: we keep trying to understand other worlds by projecting our own onto them. When the first images of Martian gullies arrived, the resemblance to Earth's water-carved ravines was so uncanny that the conclusion seemed inevitable—water, liquid and flowing, must have shaped them. But Mars is a world where water is locked away as ice or vapor, where the atmospheric pressure is so low that liquid water would boil away instantly. So if not water, what could possibly be carving these features in the present day? The answer, as Leclef's paper suggests, is carbon dioxide ice—dry ice, the same stuff that makes fog machines work. On Mars, during the cold seasons, CO₂ freezes out of the atmosphere and blankets the surface. When the sun returns, instead of melting, the ice sublimates directly into gas. This transformation can trigger violent processes: gas pressure building beneath the ice, causing it to crack and vent, or causing chunks of material to tumble down slopes, eroding gullies in a dry, explosive dance. It's a geological process that has no direct Earthly analogue, and it's happening right now, on a planet we once thought was geologically dead. What makes this story so compelling is that it's not just about Mars—it's about the limits of our imagination. We are pattern-matching machines, and when we see a gully, we think water, because on our world, that's the only way gullies form. But the universe doesn't care about our categories. It operates with a creativity that outstrips our assumptions. Every time we think we've figured out how a celestial body works, it throws us a curveball—whether it's raining diamonds on Neptune, methane lakes on Titan, or dry-ice avalanches on Mars. This is the essence of science: not the accumulation of certainties, but the joyful dismantling of them. Each "it's not water" moment is an invitation to think more broadly, to ask what else could be possible. And the answer, more often than not, is something we never would have dreamed up on our own. That's the wonder of it—the universe is not just stranger than we imagine, it's stranger than we *can* imagine, and every discovery is a reminder to keep our minds open. Source: [Universe Today](https://www.universetoday.com/articles/whats-carving-active-gullies-on-mars-its-not-water)