As the Phoenix Mars lander will agree, it’s cold near Mars’ North Pole. Phoenix is currently seeing the winter frost encroach on its location, bright patches of ice appearing on the rocks surrounding it. Another sure sign of winter at this high latitude is the loss of light; soon day will turn to night, forcing Phoenix to enter a Sun-deprived coma. But as one Mars mission draws to a close, other missions continue their diligent watch over the planet 24/7. One such mission is NASA’s Mars Reconnaissance Orbiter (MRO), using its High Resolution Imaging Science Experiment (or HiRISE for short) to pick out the tiny surface features on the Red Planet from around 320 km (200 miles) above.
As winter sets in on the Martian northern hemisphere, HiRISE continues to capture some stunning images of the translucent icy surface…
These images were acquired at the end of August by HiRISE, and it is evident there was plenty of ice on the surface of this northern region. The MRO was making a pass over a geographical latitude of 77° when these pictures were taken, capturing the complex cracking of translucent surface ice, contrasting with the dark sand of a vast number of barchan dunes, a feature we often observe on Earth as well as on Mars. Phoenix landed at 68° latitude, a little further south than these HiRISE images, but it can be seen there is a lot more ice for that time of the year only 10° further north of Phoenix’s location (after all, no surface frost was observed by the lander in August).
It is thought that the bright areas of ice in the image above comes from surface frost deposited the previous year, but the polar temperatures remained so cold throughout the Martian summer that the frost didn’t sublimate into the thin atmosphere. So, the surface ice remained throughout the year, gradually undergoing physical changes, creating a polygonal texture when viewed from orbit. The texture was probably down to temperature variations, stressing and cracking the ice.
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Looking at the detail of the sand dunes, it becomes apparent that the dunes are still active despite the icy surroundings. The streaks of loose sand appear to indicate a dominant southwesterly wind direction.