Mars Was Once a World of Rain

Mars Was Once a World of Rain By Mark Thompson - March 30, 2026 08:19 AM UTC | Planetary Science Mars is our nearest planetary neighbour and the world humans are most likely to set foot on beyond the Moon. The fourth planet from the Sun, it sits about 225 million kilometres from Earth on average, close enough that we have sent dozens of spacecraft to explore it, yet far enough to remain, in many ways, deeply mysterious. Roughly half the size of Earth, it has a day almost identical in length to ours, polar ice caps, towering volcanoes, and a canyon system that would stretch across the entire United States. But for all its surface familiarity, Mars today is a world that has been dead for a very long time with a thin atmosphere, no global magnetic field, and temperatures that plunge to minus 80 degrees Celsius on a typical night. Look at Mars today though and it's hard to imagine it was ever anything other than what it is, a cold, rust coloured desert where the wind carries dust across a landscape that hasn't seen liquid water for billions of years. But the planet's rocks remember what the atmosphere has long since forgotten. NASA’s Perseverance Mars rover took these 2 selfie versions over a rock nicknamed “Rochette,” on September 10, 2021, the 198th Martian day, or sol of the mission (Credit : NASA/Caltech) NASA's Perseverance rover has been trundling across Jezero crater since it landed in February 2021, and among the reddish debris scattered along its path it has spotted something that immediately catches the eye, white rocks. Not just a few, there are pebbles, fragments, and boulders of pale, bleached material standing out sharply against the dusty orange surroundings. Those rocks are kaolinite, an aluminium rich clay mineral, and their presence on Mars is scientifically extraordinary. On Earth, kaolinite forms in one of the most rain soaked environments imaginable….. tropical rainforests, where millions of years of heavy rainfall leach away virtually every other m...