Reanalysis of the Huygens GCMS dataset: I. High-resolution methane vertical profile in the atmosphere of Titan

Context. More than 15 years after its landing on the surface of Titan, the data returned by the Huygens probe remain the only available in situ information on Titan's lower atmosphere and its methane content. Aims. In this work, we present a reanalysis of the Huygens probe data obtained by the Gas Chromatograph Mass Spectrometer (GCMS) instrument on board Huygens. GCMS measured the atmospheric composition almost continuously during the Huygens probe descent by acquiring mass spectra between 145 km of altitude and Titan's surface. We first focus on the recollection, reconstruction, and recalibration of the GCMS dataset to facilitate similar future work. Methods. We then reevaluate the methane vertical profile in Titan's lower atmosphere by applying novel mass spectra data-treatment methods to this dataset. Results. In addition to finding a slightly lower methane mixing ratio than those previously reported using GCMS measurements above the Huygens probe landing site, our work has revealed several kilometric to subkilometric-scale oscillations in the methane vertical profile below 30 km of altitude. Conclusions. We discuss several hypotheses that could explain these features, such as multiple layers of optically thin clouds or local convection cells, and strongly encourage the reanalysis of other Huygens datasets to further investigate these variations in the methane mixing ratio.