The case for seasonal surface changes at Titan’s lake district
Résumé
Titan, Saturn’s largest moon, hosts lakes and seas of liquid hydrocarbons at its poles1. General circulation models demonstrate that regional evaporation and precipitation rates of methane are likely to change with the seasons (Titan’s year is 29.5 Earth years) and evolve on a geological timescale (~105 Earth years)2,3,4. Cassini observations suggest shoreline recession at a few south polar lakes during local summer5, but similar seasonal changes have yet to be observed at the north pole where lakes are larger and more numerous6,7. We present three ‘phantom lakes’ that appear to be north polar surface liquids in winter observations by Cassini RADAR but that are inconsistent with lakes in infrared images obtained up to seven years later, after vernal equinox, suggesting that the liquids were removed in between. If this were the case, the phantom lakes could be interpreted as shallow ponds, with either a pure methane composition or a regolith porous enough to remove the less volatile ethane. These phantom lakes provide observational constraints on removal timescales for surface liquids at Titan’s north pole. The location, size and longevity of surface liquid reservoirs affect sediment processing7, seasonal weather8, climate evolution9, and even, perhaps, their habitability10. As solubility of the possible non-polar mixtures is generally low, short-lived lakes might be nutrient-poor10 and thus have low astrobiological potential.
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