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Impacts Into Titan's Methane‐Clathrate Crust as a Source of Atmospheric Methane.

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Title: Impacts Into Titan's Methane‐Clathrate Crust as a Source of Atmospheric Methane.
Authors: Wakita, S.1,2 (AUTHOR) shigeru@mit.edu, Johnson, B. C.2,3 (AUTHOR), Soderblom, J. M.1 (AUTHOR), Steckloff, J. K.4,5 (AUTHOR), Johnson, A. V.2 (AUTHOR), Neish, C. D.4,6 (AUTHOR), Shah, J.6 (AUTHOR), Corlies, P.7 (AUTHOR)
Source: Journal of Geophysical Research. Planets. Apr2025, Vol. 130 Issue 4, p1-15. 15p.
Subject Terms: *Methane hydrates, *Atmospheric methane, *Hydrologic cycle, Natural satellites, Natural satellite atmospheres, Titan (Satellite)
Abstract: Titan is the only icy satellite in the solar system with a dense atmosphere. This atmosphere is composed primarily of nitrogen with a few percent methane, which supports an active, methane‐based hydrological cycle on Titan. The presence of methane, however, is intriguing, as its lifetime is likely much shorter than the age of the solar system due to its irreversible destruction by UV photolysis. To explain Titan's current atmospheric methane abundance, it is hypothesized that a replenishment mechanism is needed. One such mechanism may be crater forming impacts; a methane‐clathrate layer potentially covering the surface of Titan may act as a reservoir that releases methane when disrupted by impacts. Here, we perform impact simulations into methane‐clathrate layers to investigate the amount of methane released via impacts. Our simulations show that the amount of methane released into the atmosphere depends on both the impactor size and the methane‐clathrate layer thickness. A single 20‐km‐diameter impactor releases up to 1% of Titan's current atmospheric methane mass; the effect of impact obliquity and surface porosity may further increase the released mass by a factor of 2–3. The release rate from impacts is lower than the net loss rate by photolysis, but the released methane mass via impacts can enhance the lifetime of methane in Titan's atmosphere by up to 3%. Menrva‐sized (> ${ >} $400 km diameter) crater‐forming impacts directly liberate ∼ ${\sim} $15% of Titan's current atmospheric methane. The direct heating of the atmosphere by the impactor might contribute to additional crustal heating and methane release. Plain Language Summary: Titan is the only icy satellite with a dense atmosphere. Methane is the second most abundant molecule in Titan's atmosphere, but sunlight quickly destroys it, so it shouldn't be present there. To explain methane's presence in Titan's atmosphere, we may need a mechanism to resupply methane. As liquid methane soaks into Titan's icy crust, the ice may trap methane molecules and form methane clathrate. This layer would cover Titan's surface and could serve as a methane reservoir. In our work, we simulate cometary impacts into Titan's methane‐clathrate layer to determine how much methane is released. We find that the amount of methane released depends on the impactor size and the thickness of the methane‐clathrate layer: a 20‐km‐diameter impactor releases up to 1% of the current methane mass in Titan's atmosphere. The lifetime of methane would be 3% longer at the most, if we consider oblique impacts into a porous thick clathrate layer. This is not sufficient to explain the presence of methane in Titan's atmosphere. However, if multiple large impacts occurred, they would have caused a greenhouse warming effect on Titan. Key Points: To understand the presence of methane in Titan's atmosphere, we simulate impacts on Titan into a methane‐clathrate layerImpacts release methane gas that enhance its lifetime in Titan's atmosphereMultiple large impacts might release enough methane to measurably alter Titan's climate [ABSTRACT FROM AUTHOR]
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Abstract:Titan is the only icy satellite in the solar system with a dense atmosphere. This atmosphere is composed primarily of nitrogen with a few percent methane, which supports an active, methane‐based hydrological cycle on Titan. The presence of methane, however, is intriguing, as its lifetime is likely much shorter than the age of the solar system due to its irreversible destruction by UV photolysis. To explain Titan's current atmospheric methane abundance, it is hypothesized that a replenishment mechanism is needed. One such mechanism may be crater forming impacts; a methane‐clathrate layer potentially covering the surface of Titan may act as a reservoir that releases methane when disrupted by impacts. Here, we perform impact simulations into methane‐clathrate layers to investigate the amount of methane released via impacts. Our simulations show that the amount of methane released into the atmosphere depends on both the impactor size and the methane‐clathrate layer thickness. A single 20‐km‐diameter impactor releases up to 1% of Titan's current atmospheric methane mass; the effect of impact obliquity and surface porosity may further increase the released mass by a factor of 2–3. The release rate from impacts is lower than the net loss rate by photolysis, but the released methane mass via impacts can enhance the lifetime of methane in Titan's atmosphere by up to 3%. Menrva‐sized (> ${ >} $400 km diameter) crater‐forming impacts directly liberate ∼ ${\sim} $15% of Titan's current atmospheric methane. The direct heating of the atmosphere by the impactor might contribute to additional crustal heating and methane release. Plain Language Summary: Titan is the only icy satellite with a dense atmosphere. Methane is the second most abundant molecule in Titan's atmosphere, but sunlight quickly destroys it, so it shouldn't be present there. To explain methane's presence in Titan's atmosphere, we may need a mechanism to resupply methane. As liquid methane soaks into Titan's icy crust, the ice may trap methane molecules and form methane clathrate. This layer would cover Titan's surface and could serve as a methane reservoir. In our work, we simulate cometary impacts into Titan's methane‐clathrate layer to determine how much methane is released. We find that the amount of methane released depends on the impactor size and the thickness of the methane‐clathrate layer: a 20‐km‐diameter impactor releases up to 1% of the current methane mass in Titan's atmosphere. The lifetime of methane would be 3% longer at the most, if we consider oblique impacts into a porous thick clathrate layer. This is not sufficient to explain the presence of methane in Titan's atmosphere. However, if multiple large impacts occurred, they would have caused a greenhouse warming effect on Titan. Key Points: To understand the presence of methane in Titan's atmosphere, we simulate impacts on Titan into a methane‐clathrate layerImpacts release methane gas that enhance its lifetime in Titan's atmosphereMultiple large impacts might release enough methane to measurably alter Titan's climate [ABSTRACT FROM AUTHOR]
ISSN:21699097
DOI:10.1029/2024JE008624