We humans have the habit of applying our knowledge of planet Earth to justify the things we see on other planets. We can adjust the physics for different temperatures or a weaker atmosphere. But planetary scientists don’t always conclude that a similar landscape feature formed in a familiar way. As the New Horizons spacecraft gave us the first glimpse of Pluto, there were many incongruous elements. However, mountaintops dusted with something bright were located too. It resembled the snowcapped peaks of the Earth. On Earth, these snowcaps are formed by enhanced precipitation as air rises over the mountains and cools, amidst colder temperatures at higher elevations.
On Pluto, that explanation falls flat, for many reasons. At the very outset, temperatures generally rise if you go up a few kilometres from Pluto’s surface as the gases absorb solar energy. Winds blow downslope too, since the colder surface cools the air near it, making it denser. So why do the bright dusting form and how does it get there?
Towards the west of Pluto’s heart-shaped bright plain, there is a dark-coloured area called Cthulhu. In that area, there are certain mountain chains that stand out due to their shining caps. The researches claim that the dazzling areas are mostly methane ice, after analyzing spectral data from the imagery of this area. It can be located on the north-facing rims and walls of impact craters in the region too.
To understand why methane ice would form in those regions, the analysts turned to a climate model of the small planet. The model enabled ices of methane and nitrogen to form or vanish by becoming gas, and the researchers surveilled the conditions during New Horizons’ visit. By applying physics and topography, the model makes methane ice on the mountains and craters of Cthulhu with elan. Many locations can witness the formation of some methane frost at night which disappear during the day. On the contrary, a greater concentration of methane gas at higher altitudes show a net accumulation on the mountain tops over that daily cycle.
That extra methane higher up is due to the patterns of atmospheric circulation. The conduct of nitrogen ice is significant for Pluto’s atmosphere, with reticence in the northern hemisphere and contraction in the south driving north-to-south winds over the heart-shaped plains. Methane is lifted into that loop as well. The higher topography at the western edge of the plains also facilitates in pushing methane higher over Cthulhu.
The white-capped peaks are due to the methane enriched in the air around them. And on the north-facing walls and rims of the impact craters, the methane dusting is probably related to weaker sunlight during the long Plutonian winter.
Scientists assert that this pattern of methane ice accumulation at higher altitudes may explain the formation of the areas of “bladed terrain” on Pluto. These jagged ridges are also made by methane ice mostly. By comparing to the snow formation found in a few places on Earth, it was assumed that the bladed terrain was related to sublimation. Rather than sublimation deepening low spots, this study suggests a way for deposition to favour high spots. Both can happen simultaneously where one process is familiar and the other is unfamiliar.