by Wayne Jepson » Tue Sep 15, 2015 6:28 am
I've been pondering the origins of the vast ice sheet known as Sputnik Planum... My first inclination is to assume it forms much like the polar caps and glaciers of Earth, due to precipitation from the atmosphere. I've read that it's mostly frozen nitrogen, and Pluto's atmosphere is mostly nitrogen. If I'm not mistaken, the ice sheet is centered near the side of Pluto that constantly faces away from Charon, so it is closer to Pluto's equator than it's poles. Also, with Pluto's considerable axial tilt and inclined orbit, the poles as well as the equator can get fairly direct sunlight at times during it's orbit... so I'm not sure that the angle of solar rays would dictate where an ice sheet forms on Pluto, unless it's somehow related to an atmospheric circulation pattern that favors precipitation on the side of Pluto that always faces away from Charon. Further, there seems to be little evidence of "snow" accumulation a short distance away from Sputnik Planum (e.g. the dark "Cthulhu Regio" to the "south" of the ice sheet which is heavily cratered suggesting great age, but does not appear to have any "snow" or ice cover, or any signs of past erosion from past larger ice sheets). I'm at a loss to explain why atmospheric precipitation would be so localized over the eons... and it appears that Cthulhu Regio and some of the adjacent mountain ranges (Norgay and Hillary Montes) are higher in elevation than the ice sheet... if so, it's not as if it "snows" in the high elevations and the glaciers then flow down into the plains...
Which brings me to my second theory: note the large region of jumbled blocks of crust to the left of Sputnik Planum that sort of look like a giant ice floe with the bergs pushed together and then frozen in place. Note that the Montes to the "south" of the ice sheet also appear to be composed of large blocks of crust (water ice?). Further from the ice sheet, the crust is not broken up into blocks and craters are visible, suggesting a much older surface. Note the relatively smooth arc that the edge of the ice sheet makes with the older terrain, especially to the "north". Could it be that the ice sheet occupies a massive impact crater? Were the giant blocks of crust (the Montes and the chaotic terrain) along it's perimeter broken up by the impact and then frozen into place? Did the ice sheet form from upwelling / outgassing / eruption of material from deeper in the planet after the impact? Does the upwelling continue to this day, sort of like a mantle plume triggered by the impact (sort of like the formation of the Lunar Maria that fill giant craters on our moon)? Could this process be what continues to replenish Pluto's atmosphere?
I've been pondering the origins of the vast ice sheet known as Sputnik Planum... My first inclination is to assume it forms much like the polar caps and glaciers of Earth, due to precipitation from the atmosphere. I've read that it's mostly frozen nitrogen, and Pluto's atmosphere is mostly nitrogen. If I'm not mistaken, the ice sheet is centered near the side of Pluto that constantly faces away from Charon, so it is closer to Pluto's equator than it's poles. Also, with Pluto's considerable axial tilt and inclined orbit, the poles as well as the equator can get fairly direct sunlight at times during it's orbit... so I'm not sure that the angle of solar rays would dictate where an ice sheet forms on Pluto, unless it's somehow related to an atmospheric circulation pattern that favors precipitation on the side of Pluto that always faces away from Charon. Further, there seems to be little evidence of "snow" accumulation a short distance away from Sputnik Planum (e.g. the dark "Cthulhu Regio" to the "south" of the ice sheet which is heavily cratered suggesting great age, but does not appear to have any "snow" or ice cover, or any signs of past erosion from past larger ice sheets). I'm at a loss to explain why atmospheric precipitation would be so localized over the eons... and it appears that Cthulhu Regio and some of the adjacent mountain ranges (Norgay and Hillary Montes) are higher in elevation than the ice sheet... if so, it's not as if it "snows" in the high elevations and the glaciers then flow down into the plains...
Which brings me to my second theory: note the large region of jumbled blocks of crust to the left of Sputnik Planum that sort of look like a giant ice floe with the bergs pushed together and then frozen in place. Note that the Montes to the "south" of the ice sheet also appear to be composed of large blocks of crust (water ice?). Further from the ice sheet, the crust is not broken up into blocks and craters are visible, suggesting a much older surface. Note the relatively smooth arc that the edge of the ice sheet makes with the older terrain, especially to the "north". Could it be that the ice sheet occupies a massive impact crater? Were the giant blocks of crust (the Montes and the chaotic terrain) along it's perimeter broken up by the impact and then frozen into place? Did the ice sheet form from upwelling / outgassing / eruption of material from deeper in the planet after the impact? Does the upwelling continue to this day, sort of like a mantle plume triggered by the impact (sort of like the formation of the Lunar Maria that fill giant craters on our moon)? Could this process be what continues to replenish Pluto's atmosphere?