When you come to the dunes, though,

When you come to the dunes, though, they add some otherworldly strangeness. Mars’s nearly omnipresent, iron-oxide-rich, wind-blown dust imposes a palette of tan and reddish browns on almost all the planet’s landscapes, not to mention its skies. The thin line of dunes around the mountain’s base is an intervention of near perfect black, its slopes and crests likecalligraphy in India ink. This is because the dunes, unlike almost every other aspect of the Martian surface, are active. They are composed of sand from outside the crater blown against the mountain’s base, accumulating in drifts which are flowing around to the west. And those rolling sand grains gather no dust. They maintain the colour of the basalt that makes up most of the Martian crust: tarmac black. Curiosity had to look carefully for a safe passage through this Stygian flow. Active sands are no friends to rovers; one of its predecessors, Spirit, lost contact with Earth after it got stuck in a sand trap in Gusev crater. With the benefit of legs as opposed to wheels, and with muscles much stronger than is necessary in this weak gravity, you have no such fears. You can clamber up the dunes’ shallow stoss sides and slide down their steep slipfaces. You can lie down and make sand angels that sharp-eyed satellites can see from space. The pervasive out-of-placeness engendered by Mars tends to inhibit such frolics. Being alive in this barren, alien landscape is a triumphant achievement, but it is also an incipient pollution: matter out of place should know its place. But in the dunes it is different. Here Mars moves, and Mars forgets. The sands’ journey around the flanks of Mount Sharp will erase all trace of your passing. And so to the harder, steeper rock of Mount Sharp’s slopes. They are still sedimentary, but geochemically distinct from the rocks below. Curiosity spent the early years of the 2020s making sense of those distinctions as it headed towards the intriguing gully of Gediz Vallis. You are content simply to climb them, headed uptowards the wind-formed, wind-shaped strangeness of the higher reaches, your steps passing over unwitnessed and unmeasured spans of time.