Methane escape from Titan's atmosphere

Yelle, R. V.; Cui, Jun; Müller‐Wodarg, I. C. F.

doi:10.1029/2007je003031

Cited by 125 publications

(243 citation statements)

References 27 publications

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“…We approximate a diurnal average by dividing the solar fluxes by a factor of 2.0. This approach differs from the settings in Bell et al [2010aBell et al [ , 2010bBell et al [ , 2011b, but it matches other 1-D investigations of Titan's upper atmosphere [e.g., Krasnopolsky, 2009Krasnopolsky, , 2010Strobel, 2010;Yelle et al, 2008].…”

Section: Introductionmentioning

confidence: 94%

“…As found in Bell et al [2010aBell et al [ , 2010bBell et al [ , 2011b, Yelle et al [2008], andStrobel [2012], changing the magnitude of the eddy diffusion coefficient will significantly impact the amount of atmospheric escape of CH 4 required by models to reproduce the INMS densities and mixing ratios. Thus, a method for reliably capturing the effects of this turbulence is central to inferring atmospheric escape.…”

Section: Examining Different Eddy Diffusion Formulationsmentioning

confidence: 99%

“…All Rights Reserved. three methods (see Appendix A) for including turbulence in 1-D simulations: (1) the hydrostatic diffusion approach of Yelle et al [2006Yelle et al [ , 2008 and Cui et al [2012], (2) the inclusion of turbulence in the continuity equation like Strobel [2008like Strobel [ , 2009like Strobel [ , 2010like Strobel [ , 2012, and (3) the inclusion of turbulence in the momentum equation like Bell et al [2010a]. Figure 1 shows a comparison among the three methods for turbulence.…”

Section: Examining Different Eddy Diffusion Formulationsmentioning

confidence: 99%

“…Since Cassini's arrival to the Saturnian system, INMS densities and mixing ratios have been used to constrain the amount of turbulence in the upper atmosphere. In particular, Yelle et al [2008] suggested that INMS measurements of 40 Ar could act as a tracer in numerical models.…”

Section: Examining Different Eddy Diffusion Formulationsmentioning

confidence: 99%

“…Previously, we accounted for both diurnal and sun-Saturn orbital distance variations over the course of our simulations, which are not accounted for in the collective works of Cui et al [2008], Strobel [2008Strobel [ , 2009Strobel [ , 2010Strobel [ , 2012, and Yelle et al [2008]. To address these differences, we now focus on a series of simulations that approximate a global mean state during the TA-T40 timeframe, by specifying a fixed solar zenith angle of 60 • , an orbital distance of 9.25 AU, and an F 10.7−cm flux that we divide by 2.0 (see Table 1).…”

Section: Introductionmentioning

confidence: 99%

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Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

et al. 2014

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In this study, we develop a best fit description of Titan's upper atmosphere between 500 km and 1500 km, using a one‐dimensional (1‐D) version of the three‐dimensional (3‐D) Titan Global Ionosphere‐Thermosphere Model. For this modeling, we use constraints from several lower atmospheric Cassini‐Huygens investigations and validate our simulation results against in situ Cassini Ion‐Neutral Mass Spectrometer (INMS) measurements of N2, CH4, H2, 40Ar, HCN, and the major stable isotopic ratios of 14N/15N in N2. We focus our investigation on aspects of Titan's upper atmosphere that determine the amount of atmospheric escape required to match the INMS measurements: the amount of turbulence, the inclusion of chemistry, and the effects of including a self‐consistent thermal balance. We systematically examine both hydrodynamic escape scenarios for methane and scenarios with significantly reduced atmospheric escape. Our results show that the optimum configuration of Titan's upper atmosphere is one with a methane homopause near 1000 km and atmospheric escape rates of 1.41–1.47 ×1011 CH4 m−2 s−1 and 1.08 ×1014 H2 m−2 s−1 (scaled relative to the surface). We also demonstrate that simulations consistent with hydrodynamic escape of methane systematically produce inferior fits to the multiple validation points presented here.

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Section: Introductionmentioning

confidence: 94%

Section: Examining Different Eddy Diffusion Formulationsmentioning

confidence: 99%

Section: Examining Different Eddy Diffusion Formulationsmentioning

confidence: 99%

Section: Examining Different Eddy Diffusion Formulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

et al. 2014

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Ion composition in Titan's exosphere via the Cassini Plasma Spectrometer I: T40 encounter

et al. 2015

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We investigate the complex interaction between Saturn's magnetosphere and Titan's upper ionosphere using ion data acquired by the Cassini Plasma Spectrometer (CAPS) during the T40 encounter. Bounds on ion-group abundances at altitudes between~2733 and~12,541 km are determined by fitting mass spectra with model functions derived from instrument calibration data. The spectra are dominated by H + , H 2 + , H 3 + , and two hydrocarbon groups with mass ranges 12-19 and 24-32 amu, respectively. Notably, this constitutes the first reported observation of H 3 + in Titan's exosphere. These measurements are discussed in the context of data from the CAPS electron spectrometer (ELS) and the Ion and Neutral Mass Spectrometer (INMS), which fortuitously sampled the ionospheric outflow during the T40 encounter at altitudes between~2225 and~3034 km. The CAPS data reveal a composition that is constitutively similar to that sampled by INMS, with hydrocarbon ions first observed as far as~11,000 km from Titan and increasing in density by more than an order of magnitude along Cassini's inbound trajectory.In addition, we juxtapose the CAPS ion data with numerical results from three different interaction models and show that it is consistent with the location of the field-draping boundary described by Ulusen et al. (2012) and the Saturnward ion tail predicted by Sillanpää et al. (2006).

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Solar cycle variations in ion composition in the dayside ionosphere of Titan

et al. 2016

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One Titanian year spans over two complete solar cycles, and the solar irradiance has a significant effect on ionospheric densities. Solar cycle 24 has been one of the quietest cycles on record. In this paper we show data from the Cassini ion and neutral mass spectrometer (INMS) and the radio and plasma wave science Langmuir probe spanning the time period from early 2005, at the declining phase of solar cycle 23, to late 2015 at the declining phase of solar cycle 24. Densities of different ion species measured by the INMS show a consistent enhancement for high solar activity, particularly near the ionospheric peak. The density enhancement is best seen in primary ion species such as CH3+ rather than heavier ion species such as HCNH+. Unlike at Earth, where the ionosphere and atmosphere thermally expand at high solar activity, at Titan the altitude of the ionospheric peak decreases, indicating that the underlying neutral atmosphere was less extensive. Among the major ion species, CH5+ shows the largest decrease in peak altitude, whereas heavy ions such as C3H5+ show very little decrease. We also calculate the ion production rates using a theoretical model and a simple empirical model using INMS data and show that these effectively predict the increased ion production rates at high solar activity.

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Methane escape from Titan's atmosphere

Cited by 125 publications

References 27 publications

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

Ion composition in Titan's exosphere via the Cassini Plasma Spectrometer I: T40 encounter

Solar cycle variations in ion composition in the dayside ionosphere of Titan

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