New Millimeter Heterodyne Observations of Titan: Vertical Distributions of Nitriles HCN, HC3N, CH3CN, and the Isotopic Ratio 15N/14N in Its Atmosphere

Marten, A.

doi:10.1006/icar.2002.6897

Cited by 210 publications

(216 citation statements)

References 41 publications

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“…This corroborates disc-averaged ground-based studies in the sub-mm regime (e.g. Hidayat et al 1997;Marten et al 2002;Gurwell 2004;Livengood et al 2006), which also inferred abundance profiles that increased with altitude. Near the North Pole the profiles become more complicated Vinatier et al 2007).…”

Section: Introductionsupporting

confidence: 89%

Dynamical implications of seasonal and spatial variations in Titan's stratospheric composition

Teanby

Irwin

Kok

et al. 2008

Phil. Trans. R. Soc. A.

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Titan's diverse inventory of photochemically produced gases can be used as tracers to probe atmospheric circulation. Since the arrival of the Cassini-Huygens mission in July 2004 it has been possible to map the seasonal and spatial variations of these compounds in great detail. Here, we use 3.5 years of data measured by the Cassini Composite InfraRed Spectrometer instrument to determine spatial and seasonal composition trends, thus providing clues to underlying atmospheric motions. Titan's North Pole (currently in winter) displays enrichment of trace species, implying subsidence is occurring there. This is consistent with the descending branch of a single south-to-north stratospheric circulation cell and a polar vortex. Lack of enrichment in the south over most of the observed time period argues against the presence of any secondary circulation cell in the Southern Polar stratosphere. However, a residual cap of enriched gas was observed over the South Pole early in the mission, which has since completely dissipated. This cap was most probably due to residual build-up from southern winter. These observations provide new and important constraints for models of atmospheric photochemistry and circulation.

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Section: Introductionsupporting

confidence: 89%

Dynamical implications of seasonal and spatial variations in Titan's stratospheric composition

Teanby

Irwin

Kok

et al. 2008

Phil. Trans. R. Soc. A.

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“…For the thermal profile of Titan's atmosphere, we adopted the distribution used in Moreno et al (2011), a combination of the Huygens Atmospheric Structure Instrument (HASI) profile (Fulchignoni et al 2005) below 140 km, and Cassini/CIRS stratospheric temperatures ) above 140 km. The a priori molecular mixing ratios adopted in this study are those derived by Niemann et al (2010) and de Kok et al (2007) for CH 4 and CO, respectively, and the a priori profile is that derived by Marten et al (2002) for HCN. Spectroscopic parameters such as the transition frequency and the line intensity were derived from the HITRAN 2008 compilation (Rothman et al 2009), and line strengths for CH 4 were taken from Boudon et al (2010).…”

Section: Modelling the Titan Pacs Spectra And Comparing Them With Thementioning

confidence: 99%

Herschel/PACS spectroscopy of trace gases of the stratosphere of Titan

Rengel¹,

Sagawa²,

Hartogh³

et al. 2013

A&A

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Aims. We investigate the composition of Titan's stratosphere from new medium-resolution far-infrared observations performed with the full range of Herschel's Photodetector Array Camera and Spectrometer (PACS) (51-220 μm at a resolution λ/Δλ ranging from 950 to 5500 depending on wavelength and grating order). Methods. Using PACS, we obtained the spectral emission of several features of the Titan's stratosphere. We used a line-by-line radiative transfer code and the least-squares fitting technique to infer the abundances of the trace constituents. Results. Numerous spectral features attributable to CH 4 , CO, HCN, and H 2 O are present. From the flux density spectrum measured and by a detailed comparison with synthetic spectra, we constrain the stratospheric abundance of CH 4 , which is assumed to be constant with altitude, to be 1.29 ± 0.03%. Similarly, we constrain the abundance of CO to be 50 ± 2 ppm, and the HCN vertical distribution consistent with an increase from 40 ppb at ∼100 km to ∼4 ppm at ∼200 km, which is an altitude region where the HCN signatures are sensitive. Measurements of three H 2 O rotational lines confirm the H 2 O distribution profile recently obtained with Herschel. Furthermore, we determine the isotopic ratios 12 C/ 13 C in CO and HCN to be 124 ± 58, and 66 ± 35, respectively. Comparisons between our results and the values derived with other instruments show that our results are consistent with the vertical distributions and isotopic ratios in previous studies, except for the HCN distribution obtained with Cassini/CIRS, which does not agree with the PACS lines at the 1-σ confidence interval.

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“…Despite these impressive results, from which a completely new view of Titan's ion-neutral chemistry emerged, INMS cannot distinguish between species of identical mass, in particular between isomers. Heterodyne spectroscopy of strong rotational lines provides high sensitivity and frequency discrimination for the detection of minor species with permanent dipole moment -such as HCN, HC 3 N and CH 3 CN (Marten et al 2002;Gurwell 2004), and CO (Gurwell & Muhleman 1995;Hidayat et al 1998;Rengel et al 2011) -and allows for full resolution of line profiles, as well as unique absolute wind measurements in Titan's stratosphere and mesosphere from mapping of the Doppler shift in spatially-resolved data (Moreno et al 2005).…”

Section: Introductionmentioning

confidence: 99%

First detection of hydrogen isocyanide (HNC) in Titan’s atmosphere

Moreno

Lellouch

Lara

et al. 2011

A&A

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We report on the first identification of hydrogen isocyanide (HNC) in Titan's atmosphere, from observations using the HIFI instrument on the Herschel Space Observatory. An emission line from the HNC J = 6 → 5 rotational transition at 543.897 GHz was measured in Titan on June 14 and December 31, 2010. Radiative transfer modeling indicates that the bulk of HNC is located above 400 km, with a column density in the range (0.6−1.5) × 10 13 cm −2 , but the observations cannot establish its vertical profile. In particular HNC could be restricted to the upper thermosphere (∼1000 km), in which case its local abundance relative to HCN could be as high as ∼0.3. HNC is probably formed mostly at ionospheric levels (950-1150 km) from dissociative recombination of HCNH + and possibly other heavier nitrile ions. Ionospheric loss of HNC occurs by protonation with XH + ions. Additional formation (e.g. from N( 4 S) + 3 CH 2 ) and loss routes (e.g. from isomerization to HCN) in the neutral atmosphere remain to be investigated.

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New Millimeter Heterodyne Observations of Titan: Vertical Distributions of Nitriles HCN, HC3N, CH3CN, and the Isotopic Ratio 15N/14N in Its Atmosphere

Cited by 210 publications

References 41 publications

Dynamical implications of seasonal and spatial variations in Titan's stratospheric composition

Dynamical implications of seasonal and spatial variations in Titan's stratospheric composition

Herschel/PACS spectroscopy of trace gases of the stratosphere of Titan

First detection of hydrogen isocyanide (HNC) in Titan’s atmosphere

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