Modeling Far Ultraviolet Hydrocarbon Emissions in Limb Observations by New Horizons Alice at Pluto

We present results of modeling hydrocarbon emissions in the Far UltraViolet (FUV) spectrum of Pluto's upper atmosphere. Previous emission modeling efforts (Krasnopolsky, 1999; Jain and Bhardwaj, 2014; Gladstone, 2015) lack the integrated first principles photochemistry, photon transport, and spectral radiance modeling capability provided by the Atmospheric Ultraviolet Radiance Integrated Code (AURIC), which has recently been updated to include absorption and emission by multiple hydrocarbon species. Our model is compared to upper atmosphere spectral radiance data obtained by the New Horizons Alice spectrometer to test for the presence of emissions from hydrocarbons in Pluto's atmosphere including, but not limited to, ethane (C2H6), methane (CH4), and acetylene (C2H2). We utilize a maximum likelihood regression (MLR) model and forward model predictions from AURIC to determine the expected densities and intensities of hydrocarbon species, and address the possibility of detection of emission from said hydrocarbons within the signal to noise constraints of the observations.