Microphysical modeling of Titan’s detached haze layer in a 3D GCM

Larson, E. J. L.; Toon, O. B.; West, Robert A.; Friedson, A. J.

doi:10.1016/j.icarus.2015.03.010

Cited by 31 publications

(54 citation statements)

References 26 publications

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“…D f = 3 represents a spherical (nonfractal or classical Mie) particle, while D f = 1 represents a string of linearly chained monomers. Titan's fractal aggregates are thought to have a fractal dimension of about 2 on average for the aerosol population (Rannou et al , 1997; Larson et al , 2015). Note that the “effective geometric radius” we refer to above is used only to conceptualize the size of a fractal particle and does not indicate that we use Mie scattering for our fractal particles; with the exception of sub-monomer-sized particles ( R < 0.05 μm) which remain spherical and thus Mie, we use the mean field approximation for fractal scattering physics for all particles (Botet et al , 1997).…”

Section: Models and Methodsmentioning

confidence: 99%

“…Additional information about fractal particles and their geometry can be found in the works of, for example, Köylü et al (1995) and Brasil et al (1999). The mean field approximation we use for fractal scattering has been validated against scattering by silica fractal aggregates (Botet et al , 1997) and Titan's hazes (Rannou et al , 1997; Larson et al , 2015). …”

Section: Models and Methodsmentioning

confidence: 99%

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The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth

et al. 2016

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Recognizing whether a planet can support life is a primary goal of future exoplanet spectral characterization missions, but past research on habitability assessment has largely ignored the vastly different conditions that have existed in our planet's long habitable history. This study presents simulations of a habitable yet dramatically different phase of Earth's history, when the atmosphere contained a Titan-like, organic-rich haze. Prior work has claimed a haze-rich Archean Earth (3.8–2.5 billion years ago) would be frozen due to the haze's cooling effects. However, no previous studies have self-consistently taken into account climate, photochemistry, and fractal hazes. Here, we demonstrate using coupled climate-photochemical-microphysical simulations that hazes can cool the planet's surface by about 20 K, but habitable conditions with liquid surface water could be maintained with a relatively thick haze layer (τ ∼ 5 at 200 nm) even with the fainter young Sun. We find that optically thicker hazes are self-limiting due to their self-shielding properties, preventing catastrophic cooling of the planet. Hazes may even enhance planetary habitability through UV shielding, reducing surface UV flux by about 97% compared to a haze-free planet and potentially allowing survival of land-based organisms 2.7–2.6 billion years ago. The broad UV absorption signature produced by this haze may be visible across interstellar distances, allowing characterization of similar hazy exoplanets. The haze in Archean Earth's atmosphere was strongly dependent on biologically produced methane, and we propose that hydrocarbon haze may be a novel type of spectral biosignature on planets with substantial levels of CO2. Hazy Archean Earth is the most alien world for which we have geochemical constraints on environmental conditions, providing a useful analogue for similar habitable, anoxic exoplanets. Key Words: Haze—Archean Earth—Exoplanets—Spectra—Biosignatures—Planetary habitability. Astrobiology 16, 873–899.

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Section: Models and Methodsmentioning

confidence: 99%

Section: Models and Methodsmentioning

confidence: 99%

The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth

et al. 2016

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“…The larger particles are too large to have formed at higher altitudes and therefore must have been transported from a reservoir of larger particles deeper in the atmosphere [ Cours et al , ]. Larson et al [] find that the location of the detached haze layer represents the location where the upward velocity from dynamics equals the fall velocity due to gravity and thus represents the maximum combination of particles from above and below. They find that it varies seasonally because of seasonal changes in the vertical wind speeds and that it is relatively uniform with latitude because meridional motions are much faster than vertical motions.…”

Section: Seasonal Changementioning

confidence: 99%

Titan's atmosphere and climate

2017

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Titan is the only moon with a substantial atmosphere, the only other thick N2 atmosphere besides Earth's, the site of extraordinarily complex atmospheric chemistry that far surpasses any other solar system atmosphere, and the only other solar system body with stable liquid currently on its surface. The connection between Titan's surface and atmosphere is also unique in our solar system; atmospheric chemistry produces materials that are deposited on the surface and subsequently altered by surface‐atmosphere interactions such as aeolian and fluvial processes resulting in the formation of extensive dune fields and expansive lakes and seas. Titan's atmosphere is favorable for organic haze formation, which combined with the presence of some oxygen‐bearing molecules indicates that Titan's atmosphere may produce molecules of prebiotic interest. The combination of organics and liquid, in the form of water in a subsurface ocean and methane/ethane in the surface lakes and seas, means that Titan may be the ideal place in the solar system to test ideas about habitability, prebiotic chemistry, and the ubiquity and diversity of life in the universe. The Cassini‐Huygens mission to the Saturn system has provided a wealth of new information allowing for study of Titan as a complex system. Here I review our current understanding of Titan's atmosphere and climate forged from the powerful combination of Earth‐based observations, remote sensing and in situ spacecraft measurements, laboratory experiments, and models. I conclude with some of our remaining unanswered questions as the incredible era of exploration with Cassini‐Huygens comes to an end.

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“…It appears that the overturning Hadley cell determines the altitude and affects the strength of the haze layer. A more thorough description of the movement of the detached haze layer is explored in Larson et al (2014).…”

Section: Aerosol Latitudinal Distribution and Seasonal Cyclementioning

confidence: 99%