Putative Cold Seep Systems on Pluto: Analyzing Crater Morphology to Investigate Geological Sources of Methane

Large reservoirs of methane exist in the subsurface seabed of Earth’s continental margins, both as solid gas hydrate/clathrate and in its dissolved and gaseous forms¹. The transport pathways for fluids involving gas, water, and sediments are referred to as cold seeps, allowing subsurface methane to rise on the seafloor. Cold seep systems generally have three structural components: 1) the fluid source, 2) plumbing systems, and 3) venting structures or seeping features at or near the seabed such as crater-like depressions called gas pockmarks, mud volcanoes, and hydrate mounds². Optical imagery suggests that these surface features on Earth resemble morphological features on Pluto’s landscape as well. Prior works studying Pluto’s geology suggest complex geological processes such as differentiation, suggesting the formation of an ocean-insulating clathrate layer, most likely methane-derived from organic materials in Pluto’s rocky core. Crater-like depressions on the surface of Pluto may form due to fluid seepage or blowout of methane hydrate reservoirs in regions where cold seep is prevalent. The morphology of seep-related craters is geometrically distinct and with different spatial distributions from those created by impacts³. To investigate the presence of seep-related craters on Pluto, we have surveyed bright-rimmed craters by CH₄ ice in Vega Terra to investigate possible methane seepage. Pluto Global Mosaic and DEM (300 m/pixel) were used to obtain and measure topographic profiles of craters > 18 km (slightly exceeding the transition diameter) using the Java Mission-planning and Analysis for Remote Sensing (JMARS v.5.3.0) software. The topographic profiles were grouped based on the classification of pockmarks in the Danish part of the central North Sea, categorized into U, V, W-shaped, and tabular depressions⁴. Our analysis shows that 70% of the studied craters exhibit asymmetrical shapes, with a distinctive prevalence of W-shaped geometry. The remaining 30% of craters displaying circular morphology were predominantly characterized by U and V shapes, and some tabular geometry. Our results further suggest that more than half of the craters in our analysis have undergone long-term evolution, potentially linked to long-term multi-episode fluid expulsion events. We also examine their surface composition using Linear Etalon Imaging Spectral Array (LEISA) data to discern potential compositional differences between craters resulting from impact events and those with non-impact origins. Our methane generation and pathway framework can allow a more accurate assessment of the interaction between geological methane and Pluto's atmosphere.

 

References

1. Boetius, A., Wenzhöfer, F. (2013). Seafloor oxygen consumption fuelled by methane from cold seeps. Nature Geoscience, 6(9), 725-734.

2. Talukder, A. R. (2012). Review of submarine cold seep plumbing systems: leakage to seepage and venting. Terra Nova, 24(4), 255-272.

3. Stewart, S. A. (1999). Seismic interpretation of circular geological structures. Petroleum Geoscience, 5(3), 273-285.

4. Andresen, K. J., Huuse, M., & Clausen, O.R. (2008). Morphology and distribution of Oligocene and Miocene pockmarks in the Danish North Sea–implications for bottom current activity and fluid migration. Basin Research, 20(3), 445-466.