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A youthful Titan implied by improved impact simulations

Shigeru Wakita, Brandon C. Johnson, Jason M. Soderblom, Catherine D. Neish

TL;DR

This study re-evaluates Titan’s surface age by modeling impacts into icy Titan-like targets with and without a surface methane-clathrate layer using the iSALE-2D shock physics code. It derives new crater scaling laws that account for clathrate insulation and strength, revealing that craters formed in clathrate-enabled targets are typically larger than those in pure water ice, and estimates Titan’s crater retention age at $300$–$340$ Myr (versus ~420 Myr for pure ice). The results suggest Titan’s surface is geologically young and potentially shaped by recent endogenic or exogenic processes, possibly linked to past global oceans or resurfacing events, and highlight the critical role of methane clathrates in impact cratering on icy worlds. The findings offer a framework for interpreting Titan’s crater record and for assessing the influence of clathrates on planetary surfaces with methane-rich or thermally insulating crusts.

Abstract

The small number of impact craters found on Titan suggests that its surface is relatively young. Previous work estimated its surface age to be between 200 and 1000 Myr. This estimate, however, is based on crater scaling laws for water and sand, which are not representative of the composition of Titan's icy surface. Titan's surface is likely composed of water ice, methane clathrates, or a combination of both. Here, we perform impact simulations for impactors of various sizes that strike an icy target with a 0-15 km thick methane clathrate cap layer. We derive new crater scaling laws based on our numerical results, and find that Titan's surface age is 300-340 Myr, assuming heliocentric impactors and surface clathrates. This age, which represents the crater retention age, indicates a relatively youthful surface, suggesting that active endogenic and/or exogenic processes have recently reshaped Titan's surface.

A youthful Titan implied by improved impact simulations

TL;DR

This study re-evaluates Titan’s surface age by modeling impacts into icy Titan-like targets with and without a surface methane-clathrate layer using the iSALE-2D shock physics code. It derives new crater scaling laws that account for clathrate insulation and strength, revealing that craters formed in clathrate-enabled targets are typically larger than those in pure water ice, and estimates Titan’s crater retention age at – Myr (versus ~420 Myr for pure ice). The results suggest Titan’s surface is geologically young and potentially shaped by recent endogenic or exogenic processes, possibly linked to past global oceans or resurfacing events, and highlight the critical role of methane clathrates in impact cratering on icy worlds. The findings offer a framework for interpreting Titan’s crater record and for assessing the influence of clathrates on planetary surfaces with methane-rich or thermally insulating crusts.

Abstract

The small number of impact craters found on Titan suggests that its surface is relatively young. Previous work estimated its surface age to be between 200 and 1000 Myr. This estimate, however, is based on crater scaling laws for water and sand, which are not representative of the composition of Titan's icy surface. Titan's surface is likely composed of water ice, methane clathrates, or a combination of both. Here, we perform impact simulations for impactors of various sizes that strike an icy target with a 0-15 km thick methane clathrate cap layer. We derive new crater scaling laws based on our numerical results, and find that Titan's surface age is 300-340 Myr, assuming heliocentric impactors and surface clathrates. This age, which represents the crater retention age, indicates a relatively youthful surface, suggesting that active endogenic and/or exogenic processes have recently reshaped Titan's surface.
Paper Structure (8 sections, 4 equations, 3 figures)

This paper contains 8 sections, 4 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Methods
  3. Results
  4. Discussion
  5. Implications of a younger surface age
  6. The possible presence of a methane-clathrate layer
  7. Conclusions
  8. Open Research

Figures (3)

  • Figure 1: Variations in temperature (a) and yield strength (b) with depth from Titan's surface. Each line depicts a different methane-clathrate thickness (see legend). The temperature profiles follow the 1 mm ice grain results of Kalousova:2020. We model the yield strength based on temperature and other material parameters <see>Wakita:2022,Wakita:2023.
  • Figure 2: Crater diameter as a function of impactor diameter. Each color depicts a different methane-clathrate thickness (see legend). Symbols in panel a represent our impact simulation results with error bars (see Tables S1 and S2). Also shown on Panel a are published crater scaling laws for water Artemieva:2005, rock Johnson:2016c, and sand Korycansky:2005. Panel b indicates our crater scaling laws for different methane-clathrate layer thickness (see Equations (\ref{['eq:law0']})--(\ref{['eq:law15']})). The shaded region indicates craters less than 22 km in diameter, which are influenced by Titan's atmosphere <e.g.,>Artemieva:2003.
  • Figure 3: Cumulative crater count as a function of crater diameter. Each symbol and line depicts a fit to a different methane-clathrate thickness (see legend). The darkblue dotted line shows Titan's observed crater count Hedgepeth:2020. The shaded region indicates craters less than 22 km, which is the lower limit of our results. Note that those craters are affected by Titan's atmosphere, hence the drop off from the trend line. Panel b shows the inset of Panel a (a black box), so the details near the change in slope can be seen more clearly.