Decades of orbiter photographs and rover close-ups have gradually turned the red planet into something of an accidental gallery of oddities. Shadows, erosion, camera artefacts and simple pareidolia explain most of it, yet a handful of formations keep sparking double-takes across social media and space forums alike. From carved faces to shadowy doorways, here is a closer look at some of the strangest sights spotted scattered across the Martian surface so far, along with the more grounded explanations experts tend to offer for each one.