Since I've been exploring Pluto I've been puzzled by depressions in the landscape. The depression in this image is what I originally referred to as the Dried Western Basin (NASA's Piri Planitia).
These depressions have walls that appear as though they held back a fluid.
My first question is are these impressions or depressions?
An impression comes from an outward pressing force like in the case of impacts.
Dictionary.com defines depression like this.
an area completely or mostly surrounded by higher land, ordinarily having interior drainage and not conforming to the valley of a single stream.
That seems to fit the scene so depression it is.
NASA scientists interpretation of what caused these depressions is sublimation or evaporation as it eats away at the surface. This theory forces me to ask one simple question.
Why would a sublimating solid display the outline appearance of a fluid when by definition sublimation bypasses the fluid stage all together?
This depression near the south pole is covered in red tholin tar. It shows the outline of smooth walls that look like they were once containing a fluid. But not necessarily on top, we are going to have to invert our perspective to understand this.
Seems to me the red tholin would have acted like a blanket preventing surface sublimation. I don't see how sublimation can be used to describe the process at this site as well as Piri Planitia.
This image is outlining the Dried Western Basin Finger
The outline continues to naturally join its shape with the bulge outline showing how the bulge is causing the tar like tholin to slide down and create the same fluid outline as seen at the basin.
When the fluid under the bulge cools a depression will be exhibited matching the western basin's outline. Eventually this will all look like one continuous dried basin.
This demonstrates the fluid from Sputnik Planum (SP) is not filling this area but this area is recovering from shock waves and is cooling and retreating back to the area of most damage which is the southern most section of SP.