Infrared Spectroscopy Of Methane And Ethane Ices; Implications For Astronomy Studies

Abstract

The chemical composition of Pluto and Triton’s surfaces has been studied in detail using the observed reflectance spectra. By recreating these results the laboratory, the presence of contributing chemicals in the infrared spectrum has been confirmed. However, discrepancies among the observed spectra and laboratory results still remain. Strong features noted in the observed spectra have been determined through experimentation to match diluted methane, ~1%, within nitrogen ice (Quirico et al. 1999). Weaker features in the spectra are speculated to result from the presence of ethane. Previous research by DeMeo et al. 2010 demonstrates a match for diluted ethane in the spectrum of Pluto, and a debatable match for Triton. These previous studies also shed light on the possibility of ¹³CO in the observed infrared spectrum of both Triton and Pluto. A band feature in the spectrum at 2.405 μm was initially believed to be due to ¹³CO, but has been proven to be too strong to result from the presence of ¹³CO alone. The results of prior studies of C₂H₆ diluted in N₂ were limited to 21 K (DeMeo et al. 2010). It is important to expand these data to a broader range of temperatures since the surface temperatures of Triton and Pluto are expected to lie within the range of 34 and 44 K. Nitrogen ice samples containing methane and ethane in dilute quantities were recorded as binary and tertiary mixtures, for spectral comparison. These measurements were taken over a thermal range of 15 to 25 K. Recording the experimental spectra applicable to potential conditions over a range of temperatures will provide useful references for the New Horizons Mission when it arrives at Pluto in 2015. A better understanding of the spectroscopic behavior of ethane diluted in nitrogen will also provide future basis for analyzing the possibility of ¹³CO within the observed spectra.