This was
your sky.

Flowing Barchan Sand Dunes on Mars

Mars, despite its thin atmosphere where liquids freeze and evaporate quickly, shows signs of flow. Persistent winds shape large sand dunes, making them appear to move like a liquid. This image from southern Mars, taken as the season changed from spring to summer, shows two flat-topped mesas. Winds blowing from right to left have sculpted the sand on and around the hills into picturesque streaks.