ICE CHEMISTRY ON OUTER SOLAR SYSTEM BODIES: ELECTRON RADIOLYSIS OF N₂-, CH₄-, AND CO-CONTAINING ICES

Abstract

Radiation processing of the surface ices of outer Solar System bodies may be an important process for the production of complex chemical species. The refractory materials resulting from radiation processing of known ices are thought to impart to them a red or brown color, as perceived in the visible spectral region. In this work, we analyzed the refractory materials produced from the 1.2-keV electron bombardment of low-temperature N 2 -, CH 4 -, and CO-containing ices (100:1:1), which simulates the radiation from the secondary electrons produced by cosmic ray bombardment of the surface ices of Pluto. Despite starting with extremely simple ices dominated by N 2 , electron irradiation processing results in the production of refractory material with complex oxygen-and nitrogenbearing organic molecules. These refractory materials were studied at room temperature using multiple analytical techniques including Fourier-transform infrared spectroscopy, X-ray absorption near-edge structure (XANES) spectroscopy, and gas chromatography coupled with mass spectrometry (GC-MS). Infrared spectra of the refractory material suggest the presence of alcohols, carboxylic acids, ketones, aldehydes, amines, and nitriles. XANES spectra of the material indicate the presence of carboxyl groups, amides, urea, and nitriles, and are thus consistent with the IR data. Atomic abundance ratios for the bulk composition of these residues from XANES analysis show that the organic residues are extremely N-rich, having ratios of N/C ∼ 0.9 and O/C ∼ 0.2. Finally, GC-MS data reveal that the residues contain urea as well as numerous carboxylic acids, some of which are of interest for prebiotic and biological chemistries.

Photochemistry and Astrochemistry: Photochemical Pathways to Interstellar Complex Organic Molecules

“…115,203 VUV radiation and 1.2 keV electron do result in different ice resides following irradiation and heating of low-temperature N 2 :CH 4 :CO (100:1:1) ice. 204 The residues were studied by FTIR spectroscopy, X-ray absorption near-edge structure (XANES) spectroscopy, and analyzed by gas chromatography coupled to a mass spectrometer (GC-MS). The XANES analysis showed important differences in the residue structure and N/C and O/C ratios between the two sets of experiments.…”

Pluto’s global surface composition through pixel-by-pixel Hapke modeling of New Horizons Ralph/LEISA data

“…In particular, the most common are Triton tholin and Titan tholin, which are obtained by irradiating gaseous mixtures of N 2 and CH 4 . The difference between the two is in the initial N 2 to CH 4 gaseous mixing ratio (McDonald et al, 1994; Materese et al, 2015).…”

THE 3–4 μm SPECTRA OF JUPITER TROJAN ASTEROIDS

“…We suggest that the 3.1 μm absorption feature could be due to an N-H, rather than O-H stretch. Laboratory experiments of outer solar system ices which include nitrogen show the creation of residues with spectra similar to poly-HCN and absorptions at about 3.1 μm (Materese et al 2014(Materese et al , 2015. Figure 6 shows a spectrum of electron irradiated N 2 +CH 4 +CO from Materese et al (2015), and while much of the 3 μm region is dominated by water absorption (a contaminant in the laboratory measurement), an absorption peak at 3.13 μm due to N-H appears at nearly the same location as the Trojan absorption.…”