Optical constants of organic tholins produced in a simulated Titanian atmosphere: From soft x-ray to microwave frequencies

Khare, B. N.; Sagan, Carl; Arakawa, E. T.; Suits, Frank; Callcott, T. A.; Williams, M. W.

doi:10.1016/0019-1035(84)90142-8

Cited by 630 publications

(606 citation statements)

References 23 publications

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“…The refractive indices assumed were those measured for tholins (Khare et al 1984). We ran the model for three atmospheric profiles corresponding to the beginning, middle, and end of phase 2 in the protoplanet's evolution.…”

Section: Baseline Scenariomentioning

confidence: 99%

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The opacity of grains in protoplanetary atmospheres

Movshovitz

Podolak

2008

Icarus

106

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We have computed the size distribution of silicate grains in the outer radiative region of the envelope of a protoplanet evolving according to the scenario of Pollack et al. (1996). Our computation includes grain growth due to Brownian motion and overtake of smaller grains by larger ones. We also include the input of new grains due to the breakup of planetesimals in the atmosphere. We follow the procedure of Podolak (2003), but have speeded it up significantly. This allows us to test the sensitivity of the code to various parameters. We have also made a more careful estimate of the resulting grain opacity. We find that the grain opacity is of the order of 10 −2 cm 2 g −1 throughout most of the outer radiative zone as Hubickyj et al. (2005) assumed for their low opacity case, but near the outer edge of the envelope, the opacity can increase to ∼ 1 cm 2 g −1 . We discuss the effect of this on the evolution of the models.

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Section: Baseline Scenariomentioning

confidence: 99%

“…In the baseline scenario the grain opacity is calculated using a table of wavelength dependent refractive indices measured for tholins (Khare et al 1984). Figure 12 compares this opacity profile with one calculated with a refractive index table measured for olivine (Dorschner et al 1995).…”

Section: Other Parametersmentioning

confidence: 99%

The opacity of grains in protoplanetary atmospheres

Movshovitz

Podolak

2008

Icarus

106

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“…A related point is that the optical properties that we assumed for these particles were derived from measurements by Khare et al [1984] on Titan tholins. These particles were produced by charged particle irradiation of N2-CH4 mixtures.…”

Section: Uncertainties In the Calculationsmentioning

confidence: 99%

UV shielding of NH₃and O₂by organic hazes in the Archean atmosphere

Pavlov¹,

Brown²,

Kasting³

2001

J. Geophys. Res.

255

258

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Abstract. The late Archean atmosphere was probably rich in biologically generated CH4 and may well have contained a hydrocarbon haze layer similar to that observed today on Satum's moon, Titan. Here we present a detailed model of the photochemistry of haze formation in the early atmosphere, and we examine the effects of such a haze layer on climate and ultraviolet radiation. We show that the thickness of the haze layer was limited by a negative feedback loop: A haze optical depth of more than •0.5 in the visible would have produced a strong "antigreenhouse effect," thereby cooling the surface and slowing the rate at which CH 4 was produced. Given this climatic constraint on its visible optical depth, the amount of UV shielding provided by the haze can be estimated from knowledge of the optical properties and size distribution of the haze particles. Contrary to previous studies [Sagan and Chyba, 1997], we find that when the finite size of the particles is taken into account, the amount of UV shielding provided by the haze is small. Thus NH3 should have been rapidly photolyzed and should not have been sufficiently abundant to augment the atmospheric greenhouse effect. We also examine the question of whether photosynthetically generated 02 could have accumulated beneath the haze layer. For the model parameters considered here, the answer is "no": The upper limit on ground level 02 concentrations is • 10 -6 atm, and a more realistic estimate for pO2 during the late Archean is 10 -8 atm. The stability of both 02 and NH3 is sensitive to the size distribution and optical properties of the haze particles, neither of which is well known. Further theoretical and laboratory work is needed to address these uncertainties.

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“…In principle, clouds and hazes can be the result of condensation chemistry or be photochemically produced. The solar system giant planets are likely dominated by photochemical stratospheric hydrocarbon hazes (Nixon et al 2010) produced in a similar way to tholins in the atmosphere of Titan (Khare et al 1984). The strong UV flux on the upper atmosphere of hot Jupiter exoplanets may generally enhance photochemically generated hydrocarbon species.…”

Section: Introductionmentioning

confidence: 99%

Transmission spectral properties of clouds for hot Jupiter exoplanets

Wakeford

Sing

2015

A&A

189

205

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Clouds play an important role in the atmospheres of planetary bodies. It is expected that, like all the planetary bodies in our solar system, exoplanet atmospheres will also have substantial cloud coverage, and evidence is mounting for clouds in a number of hot Jupiters. To better characterise planetary atmospheres, we need to consider the effects these clouds will have on the observed broadband transmission spectra. Here we examine the expected cloud condensate species for hot Jupiter exoplanets and the effects of various grain sizes and distributions on the resulting transmission spectra from the optical to infrared, which can be used as a broad framework when interpreting exoplanet spectra. We note that significant infrared absorption features appear in the computed transmission spectrum, the result of vibrational modes between the key species in each condensate, which can potentially be very constraining. While it may be hard to differentiate between individual condensates in the broad transmission spectra, it may be possible to discern different vibrational bonds, which can distinguish between cloud formation scenarios, such as condensate clouds or photochemically generated species. Vibrational mode features are shown to be prominent when the clouds are composed of small sub-micron sized particles and can be associated with an accompanying optical scattering slope. These infrared features have potential implications for future exoplanetary atmosphere studies conducted with JWST, where such vibrational modes distinguishing condensate species can be probed at longer wavelengths.

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Optical constants of organic tholins produced in a simulated Titanian atmosphere: From soft x-ray to microwave frequencies

Cited by 630 publications

References 23 publications

The opacity of grains in protoplanetary atmospheres

The opacity of grains in protoplanetary atmospheres

UV shielding of NH₃and O₂by organic hazes in the Archean atmosphere

Transmission spectral properties of clouds for hot Jupiter exoplanets

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Optical constants of organic tholins produced in a simulated Titanian atmosphere: From soft x-ray to microwave frequencies

Cited by 630 publications

References 23 publications

The opacity of grains in protoplanetary atmospheres

The opacity of grains in protoplanetary atmospheres

UV shielding of NH3and O2by organic hazes in the Archean atmosphere

Transmission spectral properties of clouds for hot Jupiter exoplanets

Contact Info

Product

Resources

About

UV shielding of NH₃and O₂by organic hazes in the Archean atmosphere