MAVEN/IUVS Observations of the Gaseous Perturbation from Comet C/2013 A1 (Siding Spring) on Mars and its Constant Metallic Ion Layer

The close passage of comet C/2013 A1 (Siding Spring) by Mars afforded the newly arrived Mars Atmosphere and Volatile EvolutioN (MAVEN) mission the opportunity to observe a cometary perturbation to the upper atmosphere. The most dramatic atmospheric effect was the ablation of cometary dust that produced a transient metallic ion layer near 120 km, higher than the predicted (90 km) constant metallic ion layer from sporadic dust ablation due to the extreme relative velocity of the comet (56 km/s). Additionally, cometary gases such as H2O, CO2 and their daughter species delivered mass and energy to the upper atmosphere, where the temperature at 150 km was predicted to increase by 30 K. The Imaging Ultraviolet Spectrograph (IUVS) on MAVEN takes limb scans at periapse to construct altitude profiles of various ultraviolet species. Using a Multiple Linear Regression (MLR) technique to extract spectral features, we analyze the observations of the perturbed atmosphere to determine whether the gaseous mass and energy deposition is distinguishable within typical atmospheric variation. Furthermore, we use all subsequent dayside observations to identify the metallic ion layer, represented by the presence of Mg+, and compare these observations with a robust numerical model of ablation, CAMBOD (Chemical Ablation Model).