ALMA Measurements of the HNC and HC3N Distributions in Titan's atmosphere

HC3N distributions in Titan's atmosphere

We present spectrally and spatially-resolved maps of HNC and HC3N emission from Titan's atmosphere, obtained with the Atacama Large Millimeter Array (ALMA) on 2013 November 17.

These maps show anisotropic spatial distributions for both molecules, with resolved emission peaks in Titan's northern and southern hemispheres. The HC3N maps indicate enhanced concentrations of this molecule over the poles, consistent with previous studies of Titan's photochemistry and global atmospheric circulation patterns. Differences between the integrated flux distributions of HNC and HC3N show that these species are not co-spatial.

The observed spectral line shapes are consistent with HNC residing predominantly in the upper atmosphere/mesosphere (at altitudes z above 400 km), whereas HC3N is abundant at a broader range of altitudes ( z≈70−500 km). From spatial variations in the HC3N line profile, the locations of the HC3N emission peaks are shown to be variable as a function of altitude. The integrated emission peaks for HNC and the upper-atmosphere HC3N component (at z≳300 km) are found to be asymmetric with respect to Titan's polar axis, indicating that the mesosphere may be more longitudinally-variable than previously thought. Disk-averaged HNC and HC3N spectra are modeled using the RADTRANS planetary atmosphere code and the resulting best-fitting vertical mixing ratio (VMR) profiles are found to be in reasonable agreement with previous measurements for these species.

M. A. Cordiner, C. A. Nixon, N. A. Teanby, J. Serigano, S. B. Charnley, S. N. Milam, M. J. Mumma, P. G. J. Irwin, D. C. Lis, G. Villanueva, L. Paganini, Y.-J. Kuan, A. J. Remijan (Submitted on 27 Aug 2014)

Comments: Submitted to ApJ Letters

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Cite as: arXiv:1408.6461 [astro-ph.EP] (or arXiv:1408.6461v1 [astro-ph.EP] for this version)

Submission history From: Martin Cordiner PhD [v1] Wed, 27 Aug 2014 17:03:41 GMT (263kb,D)

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