The Cassini mission discovered lakes and seas comprising mostly methane in the polar regions of Titan. Lakes of liquid nitrogen may have existed during the epochs of Titan’s past in which methane was photochemically depleted, leaving a nearly pure molecular nitrogen atmosphere and, thus, far colder temperatures. The modern-day small lake basins with sharp edges have been suggested to originate from dissolution processes, due to their morphological similarity to terrestrial karstic lakes. Here we analyse the morphology of the small lake basins that feature raised rims to elucidate their origin, using delay-Doppler processed altimetric and bathymetric data acquired during the last close flyby of Titan by the Cassini spacecraft. We find that the morphology of the raised-rim basins is analogous to that of explosion craters from magma–water interaction on Earth and therefore propose that these basins are from near-surface vapour explosions, rather than karstic. We calculate that the phase transition of liquid nitrogen in the near subsurface during a warming event can generate explosions sufficient to form the basins. Hence, we suggest that raised-rim basins are evidence for one or more warming events terminating a nitrogen-dominated cold episode on Titan.
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The authors declare that the data supporting the findings of this study are available within the article and its supplementary information.
The mathematical algorithms that support findings of this study are available from the corresponding author upon request.
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The authors thank A. H. Graettinger and J. Radebaugh for useful comments. We thank A. Hayes for his constructive comments on the manuscript. G.M. expresses appreciation to A. Solomonidou for sharing her results. J.I.L. acknowledges support from the Cassini project, subcontract 1437803. V.P. acknowledges funding for this work from the NASA PDART programme grant number 80NSSC18K0513.
The authors declare no competing interests.
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Supplementary Figs. 1 and 2.