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A new numerical approach to the study of liquid methane river valleys on Titan

The Cassini-Huygens mission, which came to an end on September 15th, 2017 after a 20-year voyage, made many discoveries about Saturn, its famous rings and its many satellites, including Titan, the largest of them.

A new numerical approach to the study of liquid methane river valleys on Titan

Publication date: 17/09/2020

Press, Research

Related themes : Origins

A large number of familiar landscapes (seas, lakes, rivers, dunes, mountains, craters, etc.) have been identified on the surface of Titan, in a geological and climatic context that is nonetheless exotic: a surface composed mainly of water ice and hydrocarbons, extremely low temperatures (-180°C) and a climate based on the methane cycle. During its descent into Titan’s atmosphere in January 2005, the Huygens module identified a network of dendritic river valleys incising a hill near the landing site, similar to the networks seen on Mars and Earth.

Digital terrain model and its hydrographic network obtained by a routing algorithm. Colors are associated with altitude from 0 to 420 meters (© Daudon et al., 2020).
Mosaic of DISR images produced manually from images acquired at altitudes ranging from 250 m to 50 km. The red cross in the center of the image indicates the landing site of the Huygens probe (© E. Karkoschka, NASA/PDS, ESA).

Like water on Earth, liquid methane cuts through Titan’s substrate of water ice and/or hydrocarbons to form complex river networks. To better understand the processes responsible for the formation of these landscapes, an accurate digital terrain model (DTM) representing the topographic surface of this region is required. The first and so far only DTM of the Huygens landing site was produced by the USGS (United States Geological Survey) using photogrammetry on images acquired by DISR (Descent Imager/Spectral Radiometer) cameras. Produced in 2005 under less-than-optimal conditions (camera geometry unsuitable for photogrammetric reconstruction and small number of original images), this DTM has a number of imperfections and inconsistencies that limit its use for precise analysis of the formation of the rivers observed at this site.

Researchers at the IPGP and their international colleagues have developed a new approach, benefiting from recent DISR image processing that significantly improves the quality of the original images. To reconstruct the DTM, the scientists used MicMac, an open-source photogrammetry software package that is highly configurable. To overcome the difficulties associated with the quality of the data and the complexity of the shots (unusual geometric configuration), a specific processing chain was developed. They applied quantitative geomorphology concepts (such as river flow direction) to assess the remaining ambiguities in the overall orientation of the DTM.

Thanks to this approach, the researchers obtained a DTM covering a larger area and with much better spatial sampling than previously (18 metres, the most resolved for Titan’s surface). In fact, this new DTM significantly improves on the USGS DTM. It provides the scientific community with a fundamental tool, now accurate and unbiased, to continue the quantitative study of the formation of river valleys and the erosion and incision processes caused by liquid methane on Titan.

Ref : Daudon, C., Lucas, A., Rodriguez, S., Jacquemoud, S., Escalante López, A., Grieger, B., et al. (2020). A new digital terrain model of the Huygens landing site on Saturn’s largest moon, Titan. Earth and Space Science, 7, e2020EA001127. DOI: 10.1029/2020EA001127

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