[ESA] We’re used to seeing pictures of Mars that are very different in colour to this berry-toned view, featuring tans, ochres, reds and browns – all caused by high levels of oxidised iron. But the planet is rich in other hues, as shown beautifully in this new image from the European Space Agency’s Mars Express.
Taken by the spacecraft’s High Resolution Stereo Camera (HRSC), this image shows an icy, craggy feature known as Thyles Rupes (‘rupes’ being latin for cliff and ‘Thyles’ referring to ‘Thule’, a legendary place beyond the edge of the known world in classical geography). Its beautiful colours are obvious – but what causes them?
The darker tones are due to material that has been both made and spread by volcanoes, which leaves it rich in ‘mafic’ minerals such as olivine and pyroxene (both of which are prevalent in Earth’s mantle, the layer of rock sitting just below our planet’s crust).
Paler areas are covered by frosty deposits of carbon dioxide, which persist here even during martian spring (when this region was imaged). These blueish deposits can be seen atop sand dunes and within craters. Part of a glacier, itself part of Mars’s South Polar ice cap, can be seen to the bottom left of the frame as a pale patch of ice.
The general berry-purple hue of this scene is due to a mix of light, dust, and frost. Mars’s atmosphere is highly variable over time, meaning that images often show up in different colours throughout the day. The soft and rosy morning light here, combined with dust hanging in the air, a general ground cover of frost, and patches of mixed-up ice and dust scattered across the terrain, all come together to cause the striking purple tones we see.
Steep cliffs and frosted dunes
The rocky cliffs of Thyles Rupes can reach towering heights of over 1 km tall in some places. They are thought to be tectonic in nature, meaning that the cliffs formed as two parts of Mars’s crust were pushed together, causing one to rise up above the other. This likely happened as the interior of Mars began to cool, causing it to contract and deforming the planet’s crust above. Some blocks of Mars’s surface would have been pushed upwards via this process, forming steep cliffs – as seen here.
Unlike Earth, present-day Mars lacks active tectonics. While we see the evidence today, the processes once at play here occurred billions of years ago.
Thyles Rupes is found in the region near Mars’s south pole, in the planet’s southern highlands. It extends for hundreds of kilometres, slicing across terrain that’s heavily covered in impact craters. While some of these craters are cut through by the cliffs, indicating that they formed first and that Thyles Rupes came after, others lie on top, indicating the opposite.
Astrobiology, Astrogeology,
