The Role of Seasonal Sediment Transport and Sintering in Shaping Titan’s Landscapes

Titan is a sedimentary world, with widespread lakes1, rivers2, fans3, eroded canyonlands4, dissected plateaux5, and sand dunes6. The bulk of sediments on Saturn’s moon are thought to be largely made of mechanically weak7 organic grains8-9, possibly prone to rapid abrasion into dust. Yet, Titan’s equatorial sand dunes are thought to be relatively old (10s–100s kyr)10 and active8,10-11. Sustaining Titan’s sand dunes over geologic timescales thus requires a mechanism that produces sand-sized organic particles at equatorial latitudes7. We explore the hypothesis that a combination of sintering, when sediment grains are at rest, and abrasion, when they are transported by methane rivers or nitrogen winds, could produce sand grains with a consistent, equilibrium size. We find that episodic sintering and abrasion may readily produce sand-sized sediments under Titan’s surface conditions, and supply Titan’s equatorial dunes with well-sorted organic sand at Earth-like transport frequencies. Predictions are consistent with geologic constraints on grain sizes in the dune fields12 as well as the frequency of methane rainstorms13 and sand-transporting winds14-15. Our findings support the hypothesis of a global sedimentary cycle on Titan, driven by seasonal climate forcing, and mediated by episodic sintering and abrasion of organic sand grains by rivers and winds.

泰坦是一个沉积世界，拥有广泛分布的湖泊¹、河流²、扇状沉积体³、侵蚀峡谷区⁴、切割高原⁵及沙丘⁶。这颗土星卫星上的大部分沉积物被认为主要由力学性质脆弱⁷的有机颗粒（organic grains）⁸⁻⁹组成，这类颗粒可能易被快速磨蚀成粉尘。然而，泰坦的赤道沙丘被认为相对古老（10s–100s kyr）¹⁰且处于活跃状态⁸,¹⁰⁻¹¹。因此，要在地质时间尺度上维持泰坦的沙丘，需要一种能在赤道纬度产生沙粒级有机颗粒的机制⁷。我们探讨了如下假设：当沉积物颗粒静止时发生烧结（sintering），而当它们被甲烷河流或氮气风搬运时发生磨蚀（abrasion），这两种过程的结合或可产生尺寸稳定的平衡态沙粒。我们发现，在泰坦表面条件下，间歇性的烧结与磨蚀过程可轻易产生沙粒级沉积物，并能以类地搬运频率为泰坦赤道沙丘提供分选良好的有机沙。这些预测与沙丘区颗粒大小的地质约束¹²、甲烷暴雨¹³的频率及输沙风¹⁴⁻¹⁵的频率均一致。我们的研究结果支持泰坦存在全球沉积循环的假设，该循环由季节性气候强迫驱动，并通过河流与风对有机沙粒的间歇性烧结和磨蚀过程介导。