Methane as a reddish coating agent

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2022-08, Vol.382, p.115023, Article 115023
• Main Authors: Nørnberg, Per, Finster, Kai, Thøgersen, Jan, Golbek, Thaddeus W., Weidner, Tobias, Hassenkam, Tue, Goetz, Walter, Oehlke, Mathias, Knak Jensen, Svend J.
• Format: Article
• Language: English
• Subjects: Atmospheres; Chemistry; Prebiotic chemistry; Satellites; Spectroscopy; Surfaces
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2022.115023

Experiments in quartz ampoules that simulate the saltation of quartz grains in a methane atmosphere show that the solid phase acquires a reddish color, reminiscent of the color observed on Triton, Pluto, and Charon. Reflection spectroscopy of the coated grains show a wide, continuous absorption spectrum peaking at near-UV wavelengths, in line with the reddish color. X-ray photoelectron spectroscopy indicates the grains are coated with a substance containing CC and CO bonds, and estimates the average thickness of the surface layer to 2.3 Å. Solid state Raman measurements of the coating shows a transition at 1540 cm−1. A model is proposed to describe these measurements. The model is a polydiene, anchored to the quartz surface. Electron structure calculations show that a polydiene with around 8 CH units reproduces the measurements. AFM-IR experiments support this result. Our findings suggest a pathway for synthesis of complex molecules with CC bonds on planets and moons with a solid surface and a methane-containing atmosphere. [Display omitted] •Quartz grains in a quartz ampoule with methane are mechanically activated.•The activation mimics saltation and mediates triboelectric charging.•The activation process gives the grains a reddish color, reminiscent of the color on Triton, Pluto and Charon•The reddish color is investigated by XPS, Raman and AFM-IR experiments.•A model based on an anchored polydiene can reproduce the spectroscopic data.