Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmmr22a..03c&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #MR22A-03
Other
[5422] Planetary Sciences: Solid Surface Planets / Ices, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6008] Planetary Sciences: Comets And Small Bodies / Composition, [6261] Planetary Sciences: Solar System Objects / Triton
Scientific paper
We report the detection of the 4.76-µm fundamental absorption band of HCN ice in the spectrum of Triton obtained with the AKARI spacecraft, a 68.5-cm cryogenic telescope in space. Reflectance spectra of Triton in the range 2.5-5.0 µm obtained in both prism and grism modes of the infrared spectrograph are in good agreement, and show a rich array of molecular ices, some of which were known from earlier ground-based spectroscopic studies. The new data show the region of the fundamental bands of beta-phase N2, CO, and CO2 that were previously identified by their overtone bands at shorter wavelengths. The HCN band is clearly defined in the new spectrum at approximately five sigma above the noise level. Models of Triton’s spectrum in this region are preliminary and incomplete because of the lack of optical constants for the molecular mixture CH4:N2, which is known to dominate the spectrum throughout the near-infrared. These preliminary models suggest that HCN is present at an abundance of less than 1% by weight, consistent with its non-detection in the weaker bands at shorter wavelengths. HCN on Triton can originate from energy deposition in the abundant surface ices that contain N- and C-bearing molecules (Moore & Hudson 2003) and by UV photolysis in the thin atmosphere (Krasnopolsky & Cruikshank 1995). The AKARI data provide opportunities to test for alpha-phase N2, ethane ice, and other absorbing species, such as nitriles (and isonitriles) in addition to HCN. We find a coincidence of absorption features of the stable OCN- radical with bands in Triton’s spectrum; this radical is found in spectra of embedded protostars, constituting the principal evidence for radiation-processed ices in the interstellar medium.
Burgdorf Martin J.
Cruikshank Dale P.
Dalle Ore Cristina Morea
Sekiguchi Toyokazu
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