The Fate of Simple Organics on Titan's Surface: A Theoretical Perspective

Atmospheric photochemistry on Titan continuously transforms methane and nitrogen gases into various organic compounds. This study explores the fate of these molecules when they land on Titan's surface. Our analytical exploration reveals that most simple organics found in Titan's atmosphere, including all nitriles, triple-bonded hydrocarbons, and benzene, land as solids. Only a few compounds are in the liquid phase, while only ethylene remains gaseous. For the simple organics that land as solids, we further examine their interactions with Titan's lake liquids. Utilizing principles of buoyancy, we found that flotation can be achieved via porosity-induced (25%-60% porosity) or capillary force-induced buoyancy for hydrogen cyanide ices on ethane-rich lakes. Otherwise, these ices would sink and become lakebed sediments. By evaluating the timescale of flotation, our findings suggest that porosity-induced flotation of millimeter-sized and larger sediments is the only plausible mechanism for floating solids to explain the transient "magic islands" phenomena on Titan's lakes. Titan, Saturn's largest moon, has a unique atmosphere that transforms simple gases like methane and nitrogen into more complex organic compounds. In this study, we explored what happens to these organic compounds when they reach Titan's surface. We find that most molecules would land as solids. We also looked at what happens when these solids land on Titan's hydrocarbon lakes. Imagine a sponge, full of holes; if the solids are like this, with 25%-60% of their volume being empty space, they can float. Some solids, like hydrogen cyanide ice, can also float due to surface tension effects. If these conditions are not met, they sink into the lake liquids, adding to the lakebed sediments. We examine whether floating rafts can explain a mysterious feature on Titan's lakes known as the "magic islands." These are temporary bright spots seen by radar. By looking at how long the materials will float for each scenario, our study suggests that the magic islands might be made of large chunks of porous organic solids. Most simple organics land as solids on Titan's surface, including all nitriles, triple-bonded hydrocarbons, and benzeneOrganics may float on Titan's lakes via porosity or capillary force-induced flotation, the latter is unique to hydrogen cyanide ice on ethane-rich lakesPorosity-induced flotation of millimeter-sized and larger particles may explain the transient radar-bright magic islands on Titan's lakes