Simulation of Io's Auroral Emission: Constraints on the Atmosphere in Eclipse

• Published in: Icarus
• Main Authors: Roth, Lorenz, Saur, Joachim, Retherford, Kurt D., Strobel, Darrell F., Spencer, John R.
• Other Authors: University of Cologne, Department of Space Studies Boulder, Southwest Research Institute Boulder (SwRI), Morton K. Blaustein Department of Earth and Planetary Sciences Baltimore, Johns Hopkins University (JHU)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2011
• Subjects: Io; Jupiter; satellites; Atmospheres; structure; [SDU]Sciences of the Universe [physics]; North Pole; Hubble
• Online Access: https://hal.archives-ouvertes.fr/hal-00786874; https://hal.archives-ouvertes.fr/hal-00786874/document; https://hal.archives-ouvertes.fr/hal-00786874/file/PEER_stage2_10.1016%252Fj.icarus.2011.05.014.pdf; https://doi.org/10.1016/j.icarus.2011.05.014

International audience We study the morphology of Io's aurora by comparing simulation results of a three-dimensional (3D) two-fluid plasma model to observations by the high-resolution Long-Range Reconnaissance Imager (LORRI) on-board the New Horizons spacecraft and by the Hubble Space Telescope Advanced Camera for Surveys (HST/ACS). In 2007, Io's auroral emission in eclipse has been observed simultaneously by LORRI and ACS and the observations revealed detailed features of the aurora, such as a huge glowing plume at the Tvashtar paterae close to the North pole. The auroral radiation is generated in Io's atmosphere by collisions between impinging magnetospheric electrons and various neutral gas components. We calculate the interaction of the magnetospheric plasma with Io's atmosphere-ionosphere and simulate the auroral emission. Our aurora model takes into account not only the direct influence of the atmospheric distribution on the morphology and intensity of the emission, but also the indirect influence of the atmosphere on the plasma environment and thus on the exciting electrons. We find that the observed morphology in eclipse can be explained by a smooth (non-patchy) equatorial atmosphere with a vertical column density that corresponds to ∼10% of the column density of the sunlit atmosphere. The atmosphere is asymmetric with two times higher density and extension on the downstream hemisphere. The auroral emission from the Tvashtar volcano enables us to constrain the plume gas content for the first time. According to our model, the observed intensity of the Tvashtar plume implies a mean column density of ∼5 ×10 cm for the plume region.