Interferometric Imaging of Titan’s HC3N, H13CCCN, and HCCC15N

Cordiner, Martin; Nixon, C. A.; Charnley, Steven B.; Teanby, N. A.; Molter, Edward; Kisiel, Zbigniew; Vuitton, V.

doi:10.3847/2041-8213/aac38d

Cited by 24 publications

(19 citation statements)

References 37 publications

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“…Maps and spectra of the HC 3 N vibrationally excited lines and isotopologues have already been presented by Cordiner et al (2018), and are consistent with the overall distribution of the HC 3 N J = 40 − 39 line in Figure 1, but provide a more accurate representation of the HC 3 N column density distribution (albeit at lower S/N), due to their reduced optical depth (see Section 4.2). We also obtained high-sensitivity CO and HCN spectra (including the main J = 4 − 3 line of HCN as well as its 13 C and 15 N isotopologues).…”

Section: Spectra and Mapssupporting

confidence: 80%

“…The profile for vibrationally-excited HC 3 N (v 7 = 1) is shown in addition to the ground-state (v = 0) transition for that molecule (multiplied by 3 for display). Cordiner et al (2018) determined that the ground-state HC 3 N rotational lines in ALMA Band 7 become highly saturated at the south pole, which makes the J = 40 − 39, v = 0 transition unreliable as a measure of the HC 3 N column density at that location. The v 7 = 1 transition, by contrast, is reasonably optically thin and thus provides an improved measure of the true HC 3 N distribution.…”

Section: Latitudinal Profilesmentioning

confidence: 99%

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ALMA Spectral Imaging of Titan Contemporaneous with Cassini's Grand Finale

Cordiner

Teanby

Nixon

et al. 2019

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The Cassini mission performed 127 targeted flybys of Titan during its 13-year mission to Saturn, culminating in the Grand Finale between April-September 2017. Here we demonstrate the use of the Atacama Large Millimeter/submillimeter Array (ALMA) to continue Cassini's legacy for chemical and climatological studies of Titan's atmosphere. Whole-hemisphere, interferometric spectral maps of HCN, HNC, HC 3 N, CH 3 CN, C 2 H 3 CN, C 2 H 5 CN and C 3 H 8 were obtained using ALMA in May 2017 at moderate (≈ 0.2 , or ≈ 1300 km) spatial resolution, revealing the effects of seasonally-variable chemistry and dynamics on the distribution of each species. The ALMA sub-mm observations of HCN and HC 3 N are consistent with Cassini infrared data on these species, obtained in the same month. Chemical/dynamical lifetimes of a few years are inferred for C 2 H 3 CN and C 2 H 5 CN, in reasonably close agreement with the latest chemical models incorporating sticking of C 2 H 5 CN to stratospheric aerosol particles. ALMA radial limb flux profiles provide column density information as a function of altitude, revealing maximum abundances in the thermosphere (above 600 km) for HCN, HNC, HC 3 N and C 2 H 5 CN. This constitutes the first detailed measurement of the spatial distribution of HNC, which is found to be confined predominantly to altitudes above 730 ± 60 km. The HNC emission map shows an east-west hemispheric asymmetry of (13 ± 3)%. These results are consistent with very rapid production (and loss) of HNC in Titan's uppermost atmosphere, making this molecule an effective probe of short-timescale (diurnal) ionospheric processes.

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Section: Spectra and Mapssupporting

confidence: 80%

Section: Latitudinal Profilesmentioning

confidence: 99%

ALMA Spectral Imaging of Titan Contemporaneous with Cassini's Grand Finale

Cordiner

Teanby

Nixon

et al. 2019

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“…More specifically, the modeled 14 N/ 15 N values for CH 3 CN and C 2 H 5 CN are ∼80 at high altitudes (∼800 km) and increase to ∼120 in the lower stratosphere (∼200 km), while those for HCN and HC 3 N are expected to be relatively constant at ∼80 altitudes below 800 km. These modeled values for HCN and HC 3 N are in good agreement with previous observation results of 94±13 (Gurwell 2004) and 72.2±2.2 (Molter et al 2016) for HCN, and 67±14 (Cordiner et al 2018) for HC 3 N. Interestingly, there is another photochemical model showing different 14 N/ 15 N values for nitriles. Vuitton et al (2019) modeled nitrile chemistry including isotopic fractionation processes, which indicated that 14 N/ 15 N for CH 3 CN at high (>1000 km) altitude is smaller than that of HCN and HC 3 N because they proposed that CH 3 CN is produced from N( 2 D) which is enriched in 15 N. In turn, in the lower stratosphere (at 200 km), three nitriles are expected to exhibit similar 14 N/ 15 N values of ∼55 because non-fractionated N-atoms produced by GCR collision with N 2 homogenizes 14 N/ 15 N in nitriles via recycling processes.…”

Section: Introductionsupporting

confidence: 92%

¹⁴N/¹⁵N Isotopic Ratio in CH₃CN of Titan’s Atmosphere Measured with ALMA

Iino

Sagawa

Tsukagoshi

2020

ApJ

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Each of the nitriles present in the atmosphere of Titan can be expected to exhibit different 14 N/ 15 N values depending on their production processes, primarily because of the various N 2 dissociation processes induced by different sources such as ultraviolet radiation, magnetospheric electrons, and galactic cosmic rays. For CH 3 CN, one photochemical model predicted a 14 N/ 15 N value as 120-130 in the lower stratosphere. This is much higher than that for HCN and HC 3 N, ∼67-94. By analyzing archival data obtained by the Atacama Large Millimeter/submillimeter Array (ALMA), we successfully detected submillimeter rotational transitions of CH 3 C 15 N (J = 19-18) locate at the 338 GHz band in Titan's atmospheric spectra. By comparing those observations with the simultaneously observed CH 3 CN (J = 19-18) lines at the 349 GHz band, which probe from 160 to ∼400 km altitude, we then derived 14 N/ 15 N in CH 3 CN as 125 +145 −44 . Although the range of the derived value shows insufficient accuracy due to data quality limitations, the best-fit value suggests that 14 N/ 15 N for CH 3 CN is higher than values that have been previously observed and theoretically predicted for HCN and HC 3 N. This may be explained by the different N 2 dissociation sources according to the altitudes, as suggested by a recent photochemical model.

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“…Due to the relatively low signal-to-noise ratio of the CH 3 D and HC 3 N ν 7 = 1 lines in this observation and the large beam size compared to Titan's disk, these data are unsuitable for nuanced interpretation of latitudinal variations in Titan's atmosphere. Despite this, the spatial distribution of both HC 3 N maps are consistent with contemporaneous datasets analyzed by Cordiner et al (2017) and Thelen et al (2019), and the discrepancies in flux found between ν = 0 and vibrationally excited HC 3 N lines discussed in Cordiner et al (2018).…”

Section: Observationssupporting

confidence: 76%

Measurement of CH₃D on Titan at Submillimeter Wavelengths

Thelen

Nixon

Cordiner³

et al. 2019

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We present the first radio/submillimeter detection of monodeuterated methane (CH 3 D) in Titan's atmosphere, using archival data from of the Atacama Large Millimeter/submillimeter Array (ALMA). The J K = 2 1 − 1 1 and J K = 2 0 − 1 0 transitions at 465.235 and 465.250 GHz (∼ 0.644 mm) were measured at significance levels of 4.6σ and 5.7σ, respectively. These two lines were modeled using the Non-linear optimal Estimator for MultivariatE spectral analySIS (NEMESIS) radiative transfer code to determine the disk-averaged CH 3 D volume mixing ratio = 6.157 × 10 −6 in Titan's stratosphere (at altitudes >130 km). By comparison with the CH 4 vertical abundance profile measured by Cassini-Huygens mass spectrometry, the resulting value for D/H in CH 4 is (1.033 ± 0.081) × 10 −4 . This is consistent with previous ground-based and in-situ measurements from the Cassini/Huygens mission, though slightly lower than the average of the previous values. Additional CH 3 D observations at higher spatial resolution will be required to determine a value truly comparable with the Cassini-Huygens CH 4 measurements, by measuring CH 3 D with ALMA close to Titan's equator. In the post-Cassini era, spatially resolved observations of CH 3 D with ALMA will enable the latitudinal distribution of methane to be determined, making this an important molecule for further studies.

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Interferometric Imaging of Titan’s HC₃N, H¹³CCCN, and HCCC¹⁵N

Cited by 24 publications

References 37 publications

ALMA Spectral Imaging of Titan Contemporaneous with Cassini's Grand Finale

ALMA Spectral Imaging of Titan Contemporaneous with Cassini's Grand Finale

¹⁴N/¹⁵N Isotopic Ratio in CH₃CN of Titan’s Atmosphere Measured with ALMA

Measurement of CH₃D on Titan at Submillimeter Wavelengths

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Interferometric Imaging of Titan’s HC3N, H13CCCN, and HCCC15N

Cited by 24 publications

References 37 publications

ALMA Spectral Imaging of Titan Contemporaneous with Cassini's Grand Finale

ALMA Spectral Imaging of Titan Contemporaneous with Cassini's Grand Finale

14N/15N Isotopic Ratio in CH3CN of Titan’s Atmosphere Measured with ALMA

Measurement of CH3D on Titan at Submillimeter Wavelengths

Contact Info

Product

Resources

About

Interferometric Imaging of Titan’s HC₃N, H¹³CCCN, and HCCC¹⁵N

¹⁴N/¹⁵N Isotopic Ratio in CH₃CN of Titan’s Atmosphere Measured with ALMA

Measurement of CH₃D on Titan at Submillimeter Wavelengths