Frost in Argyre Basin on Mars

Just like on Earth, a frost can develop on Mars. What you see below is a swath of land within the 1800km wide, 5km deep Argyre Basin, which was created from an enormous impact in the early part of Mars' history. The prominent crater partially captured in this image from Mars Express' High Resolution Stereo Camera is the 138km wide Hooke Crater.

Click to see original high resolution image from Mars Express. [See their article]

The frost you see in this image is actually carbon dioxide ice, which scientists believe only forms at ground level when it freezes out of the atmosphere. The reason why only the frost is only abundant in the southern (left) lowlands of this image is because of the angle of the sun at the time this image was taken. This image was taken at 1630 local time on Mars, when the Sun was at a 20 degrees above the horizon. It only had enough time to melt the frost off the north facing crater walls, but wasn't yet able to melt any in the low lying area to the south.

Understanding when and for how long frost can cover the surface of Mars will save ...