At the edge of Sputnik Planitia, an ice-covered basin often referred to as "the heart of Pluto" due to its shape, there is a peculiar landscape of frozen parallel ridges that has no analogs anywhere else that we've explored. These washboard and fluted terrains, or WFTs, are unique to the distant dwarf planet and astronomers now have a better understanding of their origins.
As reported in Nature Astronomy, the WFTs are believed to have formed around 4 billion years ago as a result of major surface changes on Pluto. The region was at that time covered in extensive glaciers made of nitrogen ice. The glaciers formed and disappeared just after the creation of Sputnik Planitia, very early in the history of the dwarf planet. The WFTs are the debris left over from when these glaciers disappeared.
The material that makes the terrains is believed to have been buoyant in the glacial nitrogen. Due to changes in Pluto's early climate, the nitrogen went from solid to gas, a process known as sublimation. The team state that a link between sublimation and the formation of the WFTs is probable. After all, sublimation of nitrogen is also responsible for the formation of other structures around Sputnik Planitia.
Another factor that links this distinctive landscape to major changes is its orientation. The ridges all go from east-northeast to west-southwest, and this remarkably consistent orientation suggests that whatever formed the ridges is likely a global process. The exact nature of the process is still unclear.
As we have not seen such terrain anywhere else, the key to completely unraveling the mystery lies in simulations. The team suggests that laboratory studies and computer models could be used to understand the behavior of the nitrogen ice and what factors – both global and local – come into play in the formation of the WFTs. These approaches could also be used to explain several other features seen on Pluto.
If the researchers' interpretation is correct, the washboard terrain implies that the original glacier extended for 40 degrees of latitude and covered roughly 4 percent of the dwarf planet's surface. As Sputnik Planitia formed, possibly from an asteroid impact, the nitrogen ice sublimated and then recondensed in what we now see as the heart of Pluto.