It`s a Green Christmas Here in Toronto but Not on Parts of Mars

December 25, 2014

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December 25, 2014 – When I walked my dog this Christmas morning there was not a hint of snow anywhere. In fact we had to skirt puddles of water as we made our way through the local park. Autumn leaves swirled around us as we descended into a nearby ravine. This is not a Currier & Ives Christmas. At least not here where I live, and hardly anywhere in Canada, the so-called Great White North.

But on Mars, the High Resolution Imaging Science Experiment (HRISE) on NASA`s Mars Reconnaissance Orbiter, a very different image (courtesy of NASA, JPL-Caltech and the University of Arizona) suggests a white Christmas for parts of the Red Planet. The coverage area in this photograph is approximately 1.5 by 3 kilometers (approximately one mile by two). Shot in the northern hemisphere of the planet, it shows frosted gullies on the south-facing slopes of a crater while the north facing slopes, seen at the bottom right, exposed to the Sun, are frost free.

Is the frosty substance seen in these pictures made from water or carbon dioxide? More than likely predominantly the latter rather than the former. According to NASA scientists the gullies seen in this picture are formed from dry ice which is plentiful on Mars considering the atmosphere is almost entirely made up of carbon dioxide. As the dry ice sublimates into gas with seasonal changes it causes dry material on the surface to flow. Hence the gullies have steep v-shaped walls. And we know water is not involved in the erosion process because when we measure the seasonal changes we are also measuring temperature variances. And nothing that we see happening on Mars is occurring in temperatures where liquid water could flow.

That’s not to say that Mars doesn’t get water frost. Images from the Phoenix Mars Lander back in 2008 showed the formation of water-based frost on rocks in its vicinity. That thin rime of frost would vanish shortly after sunrise and reappear each day. So the White Christmas on Mars may not be all “snow white” but it sure is a lot whiter than the one I woke up to this morning.

Merry Christmas.