Rivers as witnesses of Titan's latitudinal climate variability

Abstract Titan's rich and dense atmosphere, composed mainly of methane and nitrogen, maintains a methane cycle that shapes its surface, like the water cycle on Earth. Methane precipitations erodes Titan's surface and forms complex river networks observed at all latitudes by the Cassini-Huygens mission. However, precipitation rates are poorly constrained and, in the absence of in situ measurements, understanding Titan’s global climate and meteorology is done primarily through climate models. Here, we apply a physics-based theory of river morphogenesis to provide new constraints on methane precipitation rates. In particular, we estimate the river discharges and precipitation rates required to shape two methane rivers located at the equator and south pole, which incise the surface of Titan. Our results show that the use of river morphology is relevant for inferring methane precipitation rates at various latitudes. Our estimates reduce the uncertainties from the climate models. In addition, our results reflect the climate variability between the equator and the south pole. Finally, this work sheds the light to unknown river on Earth: the giant gravel-bed rivers.