Free Astronomy Magazine November-December 2026

35 NOVEMBER-DECEMBER 2026 ASTRO PUBLISHING T his image shows Thyles Rupes on Mars in wider context. [NASA/USGS] cal geography). Its beauti- ful 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 pyrox- ene (both of which are prevalent in Earth’s man- tle, the layer of rock sit- ting just below our planet’s crust). Paler areas are covered by frosty deposits of car- bon 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 im- ages often show up in dif- ferent colours throughout the day. The soft and rosy morning light here, com- bined 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 pur- ple tones we see. The icy region at the bottom left is a mound – a patch of high elevation (see the topographic map, along- side). If it doesn’t look that way to you, instead appearing as a dip in the surface, it may be because the light is coming from a different di- rection to the one our eyes ‘expect’. The sunlight is coming from the bot- tom of the image (the east), as shown by the shadows across the scene (see the crater rim at the cen- tre of the image as an example). If you look at the icy region with this in mind, it may ‘fix’ itself – but if