The Earth may not be the biggest planet in the solar system but it is still a decent size. This mass gives it some form of stability that we will see is lacking from other planets, specifically Pluto. Pluto has a diameter of only about 18% of the Earth’s making it considerably smaller than even the Moon. On Pluto there is a massive tear shaped depression in the surface called the Sputnik Planitia, it is the pale cream area pointing towards the south pole in the picture below:
This basin is massive covering a seventh of the planet’s circumference. If Pluto was the size of the Earth and this indent scaled accordingly North America and western Europe would fit inside the basin with enough room left for possibly India or the Nordic countries. An interesting feature that can be seen quite easily in the picture above is how smooth the floor of the depression is. It doesn’t appear to be blemished by even a single crater. This is actually because the entire area is constantly in flux as volatile frozen chemicals melt, convect and refreeze.
It has been found that the scale of this excavation is so great that when the ices of nitrogen, methane and carbon monoxide, considering they are a couple of kilometres thick, become loaded to one area it can actually effect the entire planet’s moment of inertia and cause Pluto to reorientate by up to 60 degrees from its standard rotational axis. This instability, combined with a possible outwards pressure from a frozen subterranean ocean, causes cracking and pressure build ups in Pluto’s crust. Pluto is such a miniature world that what would be described as a relatively local phenomenon can affect the whole planet. Its own interior formation and constant change controls its future orientation more than could ever have been expected.