Using laboratory experiments to mimic the chemical processes in hydrogen-dominated atmospheres containing C3 and C4 hydrocarbons at elevated temperatures, Dangi et al. (2015) show that the surfaces of silicon grains can act as a catalyst, allowing the conversion of C3 and C4 hydrocarbons to carbonaceous refractory matter with carbon content greater than 90 percent. On GJ 436b, silicon grains can be supplied by micrometeoroids. This explains the low CH4 to CO ratio in the atmosphere of GJ 436b, whereby CH4 photochemically converts to higher order hydrocarbons such as C3 and C4 hydrocarbons. The catalytic surfaces of micrometeoroids then convert these hydrocarbons to refractory graphite-like carbon.
- Stevenson et al. (2010), “Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b”, arXiv:1010.4591 [astro-ph.EP]
- Dangi et al. (2015), “Toward the Formation of Carbonaceous Refractory Matter in High Temperature Hydrocarbon-rich Atmospheres of Exoplanets Upon Micrometeoroid Impact”, ApJ 805:76 (7pp)