Temperature Lapse Rate and Methane in Titan's Troposphere

McKay, Christopher P.; Martin, S. C.; Griffith, C. A.; Keller, Richard M.

doi:10.1006/icar.1997.5751

Cited by 52 publications

(22 citation statements)

References 21 publications

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“…This is significantly lower than the preferred value of 60% from McKay et al (1997). The low methane abundance is consistent with a low absolute reflectivity for the surface.…”

Section: Multiple Scatteringsupporting

confidence: 54%

“…Such a simple approach is not guaranteed to fit the constraints employed by Lellouch et al (1989), but is used only to provide a rough translation of our derived column abundance to a surface MMF. While our derived surface relative humidity value closely corresponds to the preferred value of McKay et al (1997), there are important problems with this simple analysis.…”

Section: Reflecting-layer Modelmentioning

confidence: 75%

“…McKay et al (1997) repeated the analysis of the radiooccultation data considering CH 4 -N 2 condensation and the possibility of methane supersaturation. They found that the methane relative humidity at the surface could range from 0.08 to 1.0, with values near 0.6 preferred.…”

Section: Introductionmentioning

confidence: 99%

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Methane Abundance on Titan, Measured by the Space Telescope Imaging Spectrograph

Lemmon

Smith

Lorenz

2002

Icarus

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Although methane is the dominant absorber in Titan's reflection spectrum, the amount of methane in the atmosphere has only been determined to an order of magnitude. We analyzed spectra from the Space Telescope Imaging Spectrograph, looking at both a bright surface region (700-km radius) and a dark surface region. The difference between the spectra of the two regions is attributed to light that has scattered off the surface, and therefore made a roundtrip through all of Titan's methane. Considering only absorption, the shape of the difference spectrum provides an upper limit on methane abundance of 3.5 km-am. Modeling the multiple scattering in the atmosphere further constrains the methane abundance to 2.63 ± 0.17 km-am. In the absence of supersaturation and with a simplified methane vertical profile, this corresponds to a surface methane-mole fraction near 3.8% and a relative humidity of 0.32. With supersaturation near the tropopause, the surface methane mole fraction could be as low as 3%. c 2002 Elsevier Science (USA)

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“…This is significantly lower than the preferred value of 60% from McKay et al (1997). The low methane abundance is consistent with a low absolute reflectivity for the surface.…”

Section: Multiple Scatteringsupporting

confidence: 54%

Section: Reflecting-layer Modelmentioning

confidence: 75%

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Methane Abundance on Titan, Measured by the Space Telescope Imaging Spectrograph

Lemmon

Smith

Lorenz

2002

Icarus

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“…As the methane mixing ratio varies with altitude (see e.g. McKay et al, 1997), this is not strictly correct: assuming a`realistic' mixing ratio pro®le varying from 6% at the surface to 2% at 40 km, our simpli®cation leads to a 19% overstatement of the inventory. However, the mixing ratio pro®le is not constrained by Voyager to better than a factor of two, so we retain our uniform one for convenience in our analysis.…”

Section: Constraints On Volatile Inventorymentioning

confidence: 95%

Analytic investigation of climate stability on Titan: sensitivity to volatile inventory

Lorenz

McKay

Lunine

1999

Planetary and Space Science

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We develop a semiempirical grey radiative model to quantify Titan's surface temperature as a function of pressure and composition of a nitrogen-methane-hydrogen atmosphere, solar¯ux and atmospheric haze. We then use this model, together with non-ideal gas-liquid equilibrium theory to investigate the behavior of the coupled surface-atmosphere system on Titan. We ®nd that a volatile-rich Titan is unstable with respect to a runaway greenhouseÐsmall increases in solar luminosity from the present value can lead to massive increases in surface temperature. If methane has been photolyzed throughout Titan's history, then this runaway can only be avoided if the photolytic ethane is removed from the surface-atmosphere system. #

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“…It has been found on the surface of several icy bodies in the Solar System Owen et al 1993;Brown et al 2005;Licandro et al 2006), such as the icy clouds of Jovian planets (Lindal et al 1987;Smith et al 1989), and of Saturn's moon Titan (McKay et al 1997;Griffith et al 1998;Brown et al 2002), and on the surface of Pluto and of Neptune's satellite Triton (Lanzerotti et al 1987). Methane ices have also been found throughout the interstellar medium (Lacy et al 1991;Boogert et al 1996;Gibb et al 2004;Öberg et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Cosmic ray impact on astrophysical ices: laboratory studies on heavy ion irradiation of methane

Barros

Bordalo

Duarte

et al. 2011

A&A

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Laboratory data of CH 4 ice radiolysis promoted by fast heavy ions are obtained by infrared spectroscopy (FTIR). CH 4 molecules are condensed on a CsI substrate at 15 K, and the ice layer is bombarded by 220 MeV 16 O 7+ ion beam. The ice thickness is thin enough to be traversed by projectiles at constant velocity close to the equilibrium charge state. The induced CH 4 dissociation gives rise to the formation of molecular species CH 3 , C 2 H 2 , C 2 H 4 , C 2 H 6 , and C 3 H 8 . Their formation and dissociation cross sections are determined. C 2 H 6 represent the most abundant daughter molecules. The carbon budget analysis of CH 4 and its radiolysis products shows that the column density of carbon atoms contained in the methane destroyed during ion irradiation is 30−50% greater than the sum for the column densities of the newly formed species. As an astrophysical implication, the current results allow estimation of chemical reaction rates in ices covering interstellar grains.

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Temperature Lapse Rate and Methane in Titan's Troposphere

Cited by 52 publications

References 21 publications

Methane Abundance on Titan, Measured by the Space Telescope Imaging Spectrograph

Methane Abundance on Titan, Measured by the Space Telescope Imaging Spectrograph

Analytic investigation of climate stability on Titan: sensitivity to volatile inventory

Cosmic ray impact on astrophysical ices: laboratory studies on heavy ion irradiation of methane

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