This image is probably more suited to Nancy’s “Where In The Universe” series, but judging by the resolution and surrounding landscape, it may be fairly easy to distinguish which planet and what instrument took the shot. Of course, this is Mars and the image was snapped by the astounding HiRISE instrument on board the Mars Reconnaissance Orbiter (MRO). Still… what is it? Apart from looking like a particularly large coffee stain, the answer might not be very obvious. However, once we realise this is an image of an ancient volcano covered with ice, the big question is, why has the ice melted in discrete patches when the rest of the landscape looks like a winter wonderland?
On January 16th, the MRO dashed above the southern hemisphere of Mars, over the famous Hellas impact basin. This large crater is very interesting for many reasons, particularly as the altitude distance from the crater rim to the deepest part of the crater bottom is 9 km. This means there is a 89% increase in atmospheric pressure at the bottom of the crater when compared to the planet average. The pressure is therefore high enough to entertain the thought that liquid water may be a reality in this region (if the temperature gets higher than 0°C that is).
There are also ancient volcanoes in the region, of particular note is the group of volcanoes called Malea Patera (as captured in the HiRISE image above). As Hellas is so close to the southern arctic (antarctic?) region, it is currently entering spring time, surface ice is beginning to melt as the Sun creeps higher above the Martian horizon. However, there appears to be areas of ice that are melting faster than others, and a pattern is emerging.
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At first, I looked at the images and thought that there may be some heat being released from thermal vents in the volcanic region. However, HiRISE scientists have another explanation for the dalmatian spots that have appeared. On Earth, we will often find dark rocks that appear to have melted the snow from around them during a sunny day. This is because the sunlight will penetrate the snow and heat up the darker rocks quicker than the lighter rocks. Dark rocks will absorb solar energy faster than the more reflective light rock, dark rocks heat up faster, snow surrounding dark rocks melts quicker.
This basic ice melting mechanism is being singled out for what HiRISE is seeing on this ancient volcanic region. There are patches of dark rock melting the snow faster than the rest of the region as the Sun gradually heats the southern hemisphere. What is very interesting is the patches and shape of the melt region. Could it be an ancient lava outflow from a volcano? Are the patches sand dunes peppered with volcanic material? Or is there some other explanation? HiRISE scientists hope to take more images of Malea Patera as the seasons roll on to see how the ice continues to melt. It will be interesting to see what HiRISE finds under the ice during the summer…