Optical constants of Pluto aerosol analogues from UV to near-IR

• Published in: Icarus
• Main Authors: Jovanovic, Lora, Gautier, Thomas, Broch, Laurent, Protopapa, Silvia, Bertrand, Tanguy, Rannou, Pascal, Fayolle, Marie, Quirico, Eric, Johann, Luc, Naciri, Aotmane En, Carrasco, Nathalie
• Other Authors: PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Chimie et Physique - Approche Multi-échelle des Milieux Complexes (LCP-A2MC), Université de Lorraine (UL), Southwest Research Institute Boulder (SwRI), NASA Ames Research Center (ARC), Groupe de spectrométrie moléculaire et atmosphérique (GSMA), Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG )-Université Grenoble Alpes (UGA), Delft University of Technology (TU Delft), European Project: 636829,H2020,ERC-2014-STG,PRIMCHEM(2015)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Pluto; aerosols; haze; atmosphere; Optical constants; [SDU]Sciences of the Universe [physics]; North Pole
• Online Access: https://insu.hal.science/insu-03154248; https://insu.hal.science/insu-03154248/document; https://insu.hal.science/insu-03154248/file/Jovanovic%20et%20al.%20-%20Icarus%20-%20Optical%20Constants%20of%20Pluto%20Aerosol%20Analogues%20from%20UV%20to%20near-IR.pdf; https://doi.org/10.1016/j.icarus.2021.114398

International audience Photochemical aerosols were detected as high as 350 km of altitude in Pluto's atmosphere during the New Horizons fly-by. These aerosols are thought to affect Pluto's climate, by acting as cooling agents, and the colours of Pluto's surface, in particular in the dark regions named Cthulhu and Krun and at the North Pole. Pluto atmospheric and surface models have so far used the optical constants of Titan aerosol analogues (tholins), whereas their chemical composition is known to differ from that of Pluto aerosol analogues.In order to provide a new set of optical constants for Pluto tholins, we synthesized analogues of Pluto's aerosols and determined with spectroscopic ellipsometry their optical constants from 270 to 2100 nm. Three types of samples were produced from N2:CH4:CO gas mixtures differing in their CH4:N2 mixing ratio, representative of different altitudes in Pluto's current atmosphere or different seasons or epochs of Pluto.Our analysis shows a strong absorption by Pluto tholins in the UV and visible spectral ranges, with k index of a few 10−1 at 270 nm, in agreement with N- and O-bearing organic molecules. Pluto tholins are less absorbent in the near-IR than in the UV–Vis wavelength range, with k of a few 10−3 between 600 and 2100 nm. Our comparative study highlights the dependency of n and k indices to the CH4:N2 mixing ratio. Aerosols formed at different altitudes in Pluto's atmosphere or during different seasons or epochs of Pluto will therefore affect the budget of Pluto radiative transfer differently.The optical constants presented in this study were tested with a Pluto surface model and with a model of light scattering. The surface modelling results highlight the suitability of these optical constants to reproduce Pluto compositional observations in the visible spectral range by MVIC and LEISA. The atmospheric modelling results conclude that Pluto tholins absorb 5 to 10 times less than Titan tholins at 500 nm, and this lower absorption is consistent with Alice observations ...