The Red Planet Has a Purple Side
Oxidized iron dominates the Martian colour palette. The dusty reds, ochres, browns, and tans give the planet its nickname: the Red Planet. But new images of Mars' south pole region show something different. Swirls of pink, purple, and red highlight the region and a feature named Thyles Rupes, an icy crag with cliffs higher than 1 km. Rupes means cliff in Latin, while Thyles is a mythical northern land spoken about in the ancient world.
All of the different colored materials in this region have different sources. Volcanoes both created and spread the darker material. That means that material is rich in minerals like olivine and pyroxene, both of which are also plentiful in Earth's mantle. Olivine is made of magnesium, iron, and silicate. Pyroxenes are a group of silicate minerals made mostly of silicon and oxygen, also common in Earth's upper mantle.
The pale bluish areas, like in the crater, are covered in frozen carbon dioxide. Near the south pole, this material persists, even in springtime when this image was captured. The pale patch on the lower left is actually part of the south polar cap. The main cap never melts, but a seasonal CO2 frost cap expands and contracts with the seasons.
The overall blueberry/purple hue of the region is from a combination of dust and frost. But the region doesn't always look like this and changes throughout the day. Dust in the air, soft morning light, frost covering the ground, and patches of ice and dust mixed together combine to create the purplish scene.
This image shows Thyles Rupes in context. Ultima Lingula, in the lower right, is about 550 km in diameter. Lingula means 'little tongue' in Latin, and in astrogeology, it classifies a plateau-like structures that ends in rounded, lobed shapes. Burroughs crater is named after author Edgar Rice Burroughs and is about 100 km in diameter.
Image Credit: NASA/USGS. Licence: ESA Standard Licence
Different types of dunes are also visible in the image. Due to mixed up winds, there are no finely sculpted dunes like the ones found elsewhere on Mars. There are even what are called barchanoid ridges, arc-shaped dunes common on Earth's sandy deserts that have two downwind facing "horns."
This image shows Thyles Rupes from directly above. It sits above some craters and under others, with older ones being under it. The crater on the right, the largest in the image, is older than Thyles Rupes and has been cut in half by it. Two smaller craters are visible, and they're from impacts that happened after the feature formed.
Image Credit: ESA/DLR/FU Berlin. Licence: ESA Standard Licence
Thyles Rupes, which extends for hundreds of kilometers, formed in a similar way as mountains do on Earth, when two plates push against one another. On Earth, tectonic plate movement is ongoing, forming new mountains on geological timescales. But not on Mars; it has no tectonics. It's a single-plate, stagnant lid planet. So Thyles Rupes mostly likely formed when the planet's interior was cooling. As the crust contracted, some parts were thrust upwards.
This topographic map of the region shows how tall Thyles Rupes is, more than 1 km high.
Image Credit: ESA/DLR/FU Berlin. Licence: CC BY-SA 3.0 IGO or ESA Standard Licence
Orbiters like Mars Express, featuring powerful cameras, have opened a window onto the Martian surface. Over the last couple of decades, Mars Express (and NASA's Mars Reconnaissance Orbiter) have delivered a steady stream of images of the planet's various regions. Though the planet may be dead, its surface is still intriguing, and holds many lessons about how different rocky planets can be.
