Observational Evidence for Summer Rainfall at Titan's North Pole

• Published in: Geophysical Research Letters
• Main Authors: Dhingra, Rajani, Barnes, Jason, Brown, Robert, Burrati, Bonnie, Sotin, Christophe, Nicholson, Phillip, Baines, Kevin, Clark, Roger, Soderblom, Jason, Jauman, Ralf, Rodriguez, Sebastien, Mouélic, Stéphane, Turtle, Elizabeth, Perry, Jason, Cottini, Valeria, Jennings, Don
• Other Authors: Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Cornell University New York, MIT, Earth Atmospher & Planetary Sci, 77 Massachusetts Ave, Cambridge, MA 02139 USA, DLR Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt Berlin (DLR), Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Johns Hopkins University Applied Physics Laboratory Laurel, MD (APL), NASA Goddard Space Flight Center (GSFC)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: [PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP]; North Pole; South Pole; South pole
• Online Access: https://u-paris.hal.science/hal-03657898; https://u-paris.hal.science/hal-03657898/document; https://u-paris.hal.science/hal-03657898/file/Dhingra_et_al-2019-Geophysical_Research_Letters.pdf; https://doi.org/10.1029/2018gl080943

International audience Methane rain on Saturn's moon Titan makes it the only place, other than Earth, where rain interacts with the surface. When and where that rain wets the surface changes seasonally in ways that remain poorly understood. Here we report the discovery of a bright ephemeral feature covering an area of 120,000 km 2 near Titan's north pole in observations from Cassini's near-infrared instrument, Visual and Infrared Mapping Spectrometer on 7 June 2016. Based on the overall brightness, spectral characteristics, and geologic context, we attribute this new feature to specular reflections from a rain-wetted solid surface like those off of a sunlit wet sidewalk. The reported observation is the first documented rainfall event at Titan's north pole and heralds the arrival of the northern summer (through climatic evidence), which has been delayed relative to model predictions. This detection helps constrain Titan's seasonal change and shows that the "wet-sidewalk effect can be used to identify other rain events." Plain Language Summary Cassini arrived in the Saturnian system in the southern summers of 2004. As expected, the Cassini team observed cloud cover, storms, and precipitation on the south pole. Like Earth, Titan has an axial tilt (27 •) and its seasons vary over its year (30 Earth years). Ever since this shift in season began, the Cassini team eagerly waited for observations indicating cloud cover and precipitation that went missing from the northern latitudes. Our rainfall observation at the north pole is a major finding for two important reasons. First, this discovery observation heralds the much awaited arrival of the north polar summer rainstorms on Titan. This atmospheric phenomenon has been delayed compared to the theoretical predictions and was perplexing Titan researchers and climate modelers especially because the north pole hosts most of Titan's lakes and seas. Second, it is extremely difficult to detect rainfall events on Titan due to its thick atmospheric haze and very limited ...