Images taken by the European Space Agency’s Mars Express orbiter show what look like hints of blue, liquid in the Arabia Terra region of Mars’ surface. According to the ESA, these blue areas are dark sediments that have built up over time. On the red planet, winds can hit 100 km/h; as these winds travel they erode and gradually wear away the planet’s surface features over millions of years. They also cause sediment build-up, carrying dark, volcanic, basalt-rich deposits across the planet that get trapped in the craters pockmarking the landscape. Over time, enough of the darker dust collects on the crater’s surface and appears as these blue patches.