DISSOLUTION GEOMORPHOLOGY AT 90 K ON SATURN’S MOON TITAN
Since 2006, Cassini’s RADAR instrument has revealed 100s of lakes and lake basins in the Arctic region. Their morphologies exhibit a non-random spatial distribution, from smaller (a few km) steep-sided quasi-circular depressions in the western hemisphere, to larger seas with rugged shorelines in the lower elevation eastern. Lake basins with bright (un-filled) as opposed to dark (filled) interiors tend towards lower (<~70 deg) arctic latitudes and/or higher elevations, hence more arid environs. Steep-sided basins are up to 100s of m from rim to floor, and typically 1s to 10s of km across. Small, steep-sided lakes tend to exist at higher elevations in the western hemisphere, with more diffusely margined seas at lower elevations in the east. Floors tend towards elevations lying somewhere between the gravitational equipotential surface, and the gently sloping regional terrain.
The correlation between surface liquids and lake basins and their almost uniquely high latitude geographic distribution, in Antarctic as well as Arctic contexts supports a bi-directional causal (limnogenic) relationship between surface liquids and basins. We rule out glacial origin due to a lack of suitable mobile solids, and thermokarstic for reasons of energy balance. Our preferred interpretation for the small, steep-sided and quasi-circular lakes is one involving chemical dissolution, suffosion, collapse, and subsurface flow, much like terrestrial karst. This is consistent with Titan’s suspected surface chemistry, as some of the organic solids are highly soluble in liquid alkanes. Other surface features resemble terrestrial karstic landscapes, including tower karst, poljes, fluviokarst, and corrosion plains, strengthening the interpretation.
From a process-based perspective, this would be the first observation of an active karstic landscape forming on an alien world.