Frosty scene at the south pole of Mars

At first glance this looks like a beautiful winter wonderland scene, with layers of snow and ice hugging the hilltops. But this is almost summer at the south pole of Mars, and the Sun’s warming rays are causing the seasonal ice layers to retreat. 

Zooming into the left hand side of the image reveals numerous dark patches where the ice has already sublimated away (turned directly from solid ice into vapour). 

When sunlight shines through the translucent top layers of the carbon dioxide ice it warms up the underlying surface. The ice at the bottom of the layer begins to sublimate, creating pockets of trapped gas. The pressure builds up until the overlying ice suddenly cracks, resulting in a burst of gas jetting through the surface. These gas fountains carry dark dust from below, which falls back to the surface in a fan-shaped pattern moulded by the direction of the prevailing wind. The fans can range in length from tens to hundreds of metres.

The fans also follow the boundaries between the layered ice-dust deposits characteristic of the seasonal ice cap, and especially evident in the left side of the image.

This colour image comprises data gathered by Mars Express’s High Resolution Stereo Camera (HRSC) on 16 June 2022 (orbit 23324). It was created using data from the nadir channel, the field of view which is aligned perpendicular to the surface of Mars, and the colour channels of the HRSC. The ground resolution is approximately 15 m/pixel and the image is centred at about 239°E/84°S. North is to the right.

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[Image description: Swirls of light and dark layers mark the boundaries between ice and dust layers exposed in this icy scene. The right side of the image has a lot of ice coverage compared with the left hand side that has numerous dark fan-shaped deposits tracing the horizontal layers.]