Scientists at NASA have found what appears to be a giant "bite mark" on Pluto's western hemisphere, and they are now taking a closer look at what kind of process may have caused this particular feature.
In order to better understand geological features on a distant planet, researchers look at all the areas surrounding that feature. This allows them to compare what they see to features that they may have seen on other planets in order to determine exactly what the feature is.
In this case, the researchers looked closer at Piri Rupes, which is near the "bite mark" on Pluto. If you go diagonally across the mottled plains on Pluto's surface, you'll find the long extension fault called Inanna Fossa. This stretches eastward 370 miles to the edge of the nitrogen ice plains called Sputnik Planum.
Compositional data from the New Horizons spacecraft actually indicates that the plateau uplands south of Piri Rupes are rich in methane ice. Currently, researchers believe that the sublimation of methane, which is when a solid turns into a gas, may be causing the plateau material to erode along the face of the cliffs. In other words, it's causing the material to retreat south and leaves the plains known as Piri Planitia behind.
But what is Piri Planitia like? Other compositional data shows that the surface of these plains has more water ice than the higher plateaus on Mars. This may actually mean that the plains consist of water ice bedrock located just beneath a layer of methane ice that's retreating due to sublimation. Because the surface of Pluto is so cold, the water-ice is more rock-like than liquid-like. This means that it is, effectively, immobile.
So what exactly is the bite mark? It's likely the result of the retreating methane ice with the hard water-ice visible beneath.
While this may seem like a small finding, it's important for understanding the environment on Pluto. This tiny planet is showing researchers that it had surprising features in its geologic past. With canyons, cliffs and ice, this planet is far more dynamic than anyone expected before the New Horizons mission took place.
