Surface ices and the atmospheric composition of pluto.

Science (Impact Factor: 31.48). 09/1993; 261(5122):745-8. DOI: 10.1126/science.261.5122.745
Source: PubMed

ABSTRACT Observations of the 1.4- to 2.4-micrometer spectrum of Pluto reveal absorptions of carbon monoxide and nitrogen ices and confirm the presence of solid methane. Frozen nitrogen is more abundant than the other two ices by a factor of about 50; gaseous nitrogen must therefore be the major atmospheric constituent. The absence of carbon dioxide absorptions is one of several differences between the spectra of Pluto and Triton in this region. Both worlds carry information about the composition of the solar nebula and the processes by which icy planetesimals formed.

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    ABSTRACT: Based on the vapor pressure behavior of Pluto's surface ices, Pluto's atmosphere is expected to be predominantly composed of N2 gas. Measurement of the N2 isotopologue 15N/14N ratio within Pluto's atmosphere would provide important clues to the evolution of Pluto's atmosphere from the time of formation to its present state. The most straightforward way of determining the N2 isotopologue 15N/14N ratio in Pluto's atmosphere is via spectroscopic observation of the 14N15N gas species. Recent calculations of the 80–100 nm absorption behavior of the 14N2 and 14N15N isotopologues by Heays et al. (Heays, A.N. et al. [2011]. J. Chem. Phys. 135, 244301), Lewis et al. (Lewis, B.R., Heays, A.N., Gibson, S.T., Lefebvre-Brion, H., Lefebvre, R. [2008]. J. Chem. Phys. 129, 164306); Lewis et al. (Lewis, B.R., Gibson, S.T., Zhang, W., Lefebvre-Brion, H., Robbe, J.-M. [2005]. J. Chem. Phys. 122, 144302), and Haverd et al. (Haverd, V.E., Lewis, B.R., Gibson, S.T., Stark, G. [2005]. J. Chem. Phys. 123, 214304) show that the peak magnitudes of the 14N2 and 14N15N absorption bandhead cross-sections are similar, but the locations of the bandhead peaks are offset in wavelength by ˜0.05–0.1 nm. These offsets make the segregation of the 14N2 and 14N15N absorption signatures possible. We use the most recent N2 isotopologue absorption cross-section calculations and the atmospheric density profiles resulting from photochemical models developed by Krasnopolsky and Cruickshank (Krasnopolsky, V.A., Cruickshank, D.P. [1999]. J. Geophys. Res. 104, 21979–21996) to predict the level of solar light that will be transmitted through Pluto's atmosphere as a function of altitude during a Pluto solar occultation. We characterize the detectability of the isotopic absorption signature per altitude assuming 14N15N concentrations ranging from 0.1% to 2% of the 14N2 density and instrumental spectral resolutions ranging from 0.01 to 0.3 nm. Our simulations indicate that optical depth of unity is attained in the key 14N15N absorption bands located between 85 and 90 nm at altitudes ˜1100–1600 km above Pluto's surface. Additionally, an 14N15N isotope absorption depth ˜4–15% is predicted for observations obtained at these altitudes at a spectral resolution of ˜0.2–0.3 nm, if the N2 isotopologue 15N/14N percent ratio is comparable to the 0.37–0.6% ratio observed at Earth, Titan and Mars. If we presume that the predicted absorption depth must be at least 25% greater than the expected observational uncertainty, then it follows that a statistically significant detection of these signatures and constraint of the N2 isotopologue 14N/15N ratio within Pluto's atmosphere will be possible if the attainable observational signal-to noise (S/N) ratio is ⩾9. The New Horizons (NH) Mission will be able to obtain high S/N, 0.27–0.35 nm full-width half-max 80–100 nm spectral observations of Pluto using the Alice spectrograph. Based on the NH/Alice specifications we have simulated 0.3 nm spectral resolution solar occultation spectra for the 1100–1600 km altitude range, assuming 30 s integration times. These simulations indicate that NH/Alice will obtain spectral observations within this altitude range with a S/N ratio ˜25–50, and should be able to reliably detect the 14N15N gas absorption signature between 85 and 90 nm if the 14N15N concentration is ˜0.3% or greater. This, additionally, implies that the non-detection of the 14N15N species in the 1100–1600 km range by NH/Alice may be used to reliably establish an upper limit to the N2 isotopologue 15N/14N ratio within Pluto's atmosphere. Similar results may be derived from 0.2 to 0.3 nm spectral resolution observations of any other N2-rich Solar System or exoplanet atmosphere, provided the observations are attained with similar S/N levels.
    Icarus 11/2013; 226(2):1514-1526. · 2.84 Impact Factor
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    ABSTRACT: Contents: The formation of solar-system objects and the abundance of CO: the condensation sequence, the CO/CH4 ratio; heterodyne spectroscopy measurements of CO in the solar system: Venus and Mars, the giant planets, the outer satellites and Pluto, comets; perspectives and future plans.
    Proceedings of the International Astronomical Union 01/1997;
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    ABSTRACT: We present new experimental results concerning the implantation of multiply charged sulfur ions (90 and 176 keV) in frozen CO and CO2. CO2 layers have been capped with a water ice layer to study chemical reactions induced at the interface between the two species. The results indicate that SO2 is formed after implantation in both CO and CO2 and the respective formation yields are 0.20 ± 0.05 and 0.38 ± 0.20 molecules ion-1 for 176-keV S11+ in CO and 90-keV S9+ in CO2, respectively. Possibly, CS2 has been produced in CO2 and OCS in CO. Ion implantation produces also all of the chemical modifications observed with other ion beam. In particular a large number of carbon chains are formed after implantation in CO. Chemical reactions and mixing are induced at the water/carbon dioxide interface and lead to the formation of carbonic acid (H2CO3). The results are discussed in the light of their relevance in some astrophysical environments both in the star-forming regions and in the Solar system.
    Monthly Notices of the Royal Astronomical Society 12/2013; · 5.23 Impact Factor

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