Downhill sledding at 40 AU: Mobilizing Pluto's chaotic mountain blocks

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2021-03, Vol.356, p.113829, Article 113829
• Main Authors: O'Hara, Sean T., Dombard, Andrew J.
• Format: Article
• Language: English
• Subjects: Geological processes; Geophysics; Ices; Mechanical properties; Pluto; Surface
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2020.113829

We present a force-balance analysis of the mobilization and emplacement of the large mountain block chains observed on the western rim of Pluto's Sputnik Planitia basin. These mountain blocks are likely disrupted pieces of Pluto's water ice crust that are grounded in the nitrogen ice that fills the basin. After fracturing from the basin rim, they could have slid downslope into the basin under their own weight on timescales as short as hundreds to thousands of years, collecting into the observed ranges where the basin slope shallows below a critical value. This movement would require a lubricating fluid, most likely nitrogen, to be present at the base of the blocks. Traction from flowing nitrogen glaciers could have initiated or aided transport for blocks that are small enough to be at least halfway immersed by the nitrogen. Lateral convective forces within the nitrogen ice sheet did not play a significant role in the mobilization of all but the smallest of the observed blocks that likely float buoyantly in the nitrogen ice. If the blocks did emplace by basal sliding, the requirement that liquid nitrogen be present to provide lubrication provides a key to Pluto's past climate history. This work adds to the body of evidence that erosional features and other surface modification could have been driven by the surface or near-surface flow of liquid nitrogen resulting from global climate change on Pluto. •Pluto's mountain block ranges could have formed by gravity-driven basal sliding.•Basal lubrication from liquid nitrogen is required, implying global climate change.•Emplacement times by this mechanism are very short, as low as hundreds of years.•Blocks could also be carried by glaciers if they were sufficiently submerged.