Cryptic Mars landscape revealed as ice thaws in southern hemisphere

The polar caps on Mars consist mostly of carbon dioxide ice, with some water ice. During spring, the ice sublimates, releasing gas into Mars' atmosphere. By late winter, these ice caps extend to approximately 55 degrees latitude, comparable to areas as far south as Scotland on Earth.

This annual freeze-thaw cycle results in unique surface formations. Captured by Mars Express' High Resolution Stereo Camera (HRSC) on April 2, 2024, these images show the Australe Scopuli region near Mars' south pole, revealing a variety of polar features. The scene is split between layered ice deposits and smooth terrain.

The central portion of the image is dominated by the cryptic terrain. Once mysterious, scientists now better understand the processes that create these dark regions.

Periglacial patterns
Zooming into the cryptic terrain reveals polygonal shapes formed by ridges and troughs, which sometimes trap bright frost. These formations are periglacial, commonly seen in Earth's polar regions, where the freeze-thaw cycle of water ice shapes the landscape over years or centuries. Studying them on Mars can provide insights into the planet's climate history.

Jets and fans
Throughout the image, fan-shaped deposits can be observed, oriented by prevailing winds. These formations arise when trapped gas beneath a translucent ice layer in early spring escapes, ejecting dark dust that forms fan-like deposits on the ice. The darker dust then warms the ice beneath, accelerating sublimation and creating holes, revealing fresh ice or new frost.

This process is unique to the Martian spring and helps explain the formation of the dark cryptic features.

Exploring Mars
Mars Express, which entered orbit in 2003, has been instrumental in tracking seasonal changes on the planet, allowing researchers to better understand its dynamic features. The HRSC has revealed not just the planet's ice caps but also its geological features, from volcanoes and river channels to impact craters and tectonic faults.

The longevity of Mars Express has provided a more comprehensive view of Mars, enabling a fuller understanding of the planet's atmosphere, mineral composition, and geological history.

The Mars Express High Resolution Stereo Camera (HRSC) was developed and is operated by the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR).