Titan-like exoplanets: Variations in geometric albedo and effective transit height with haze production rate

Checlair, J.; McKay, Christopher P.; Imanaka, Hiroshi

doi:10.1016/j.pss.2016.03.012

Cited by 9 publications

(17 citation statements)

References 49 publications

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“…Laboratory experiments investigating the chemical precursors, pathways, and energy sources that lead to Titan-like hazes and their resulting composition (Cable et al 2012;Hörst & Tolbert 2013;Hörst et al 2017;Imanaka & Smith 2010;Trainer et al 2013;Sciamma-O'Brien et al 2014) are critical to improving our understanding of the formation of exoplanetary hazes, including its dependence on external factors like stellar forcing. Thus, the combination of such ongoing laboratory work and modeling like ours-along with various observations, including short wavelength studies that might probe the existence of haze (Checlair et al 2016)-is required to make further progress in characterizing the diversity of hazy, cool, terrestrial exoplanets.…”

Section: Resultsmentioning

confidence: 99%

“…More recently, the studies of Robinson et al (2014) and Checlair et al (2016) illustrated the potential for future observational characterization of Titan-like exoplanets. Robinson et al (2014) used Cassini/VIMS occultation observations to understand what Titan would look like in transit (i.e, passing in front of the Sun along the line of sight of some faraway observer).…”

Section: Introductionmentioning

confidence: 99%

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Atmospheric Circulation, Chemistry, and Infrared Spectra of Titan-like Exoplanets around Different Stellar Types

Lora

Kataria

2018

ApJ

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With the discovery of ever smaller and colder exoplanets, terrestrial worlds with hazy atmospheres must be increasingly considered. Our Solar System's Titan is a prototypical hazy planet, whose atmosphere may be representative of a large number of planets in our Galaxy. As a step towards characterizing such worlds, we present simulations of exoplanets that resemble Titan, but orbit three different stellar hosts: G-, K-, and M-dwarf stars. We use general circulation and photochemistry models to explore the circulation and chemistry of these Titan-like planets under varying stellar spectra, in all cases assuming a Titan-like insolation. Due to the strong absorption of visible light by atmospheric haze, the redder radiation accompanying later stellar types produces more isothermal stratospheres, stronger meridional temperature gradients at mbar pressures, and deeper and stronger zonal winds. In all cases, the planets' atmospheres are strongly superrotating, but meridional circulation cells are weaker aloft under redder starlight. The photochemistry of hydrocarbon and nitrile species varies with stellar spectra, with variations in the FUV/NUV flux ratio playing an important role. Our results tentatively suggest that column haze production rates could be similar under all three hosts, implying that planets around many different stars could have similar characteristics to Titan's atmosphere. Lastly, we present theoretical emission spectra. Overall, our study indicates that, despite important and subtle differences, the circulation and chemistry of Titan-like exoplanets are relatively insensitive to differences in host star. These findings may be further probed with future space-based facilities, like WFIRST, LUVOIR, HabEx, and OST.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Atmospheric Circulation, Chemistry, and Infrared Spectra of Titan-like Exoplanets around Different Stellar Types

Lora

Kataria

2018

ApJ

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“…We then numerically integrate that extinction (using qromb from Press et al 1992) along the photon's traverse to calculate the cumulative τ between the photon's present position and each position d. While the original IDL code on which SRTC++ builds uses an analytic approximation to the Chapman Integral (Smith & Smith 1972), we instead evaluate the integrated optical depth numerically. While the numerical approach slows program execution, Checlair et al (2016) shows that the compromises inherent to the (Smith & Smith 1972) approximation in puffy atmospheres like Titan's result in 10% systematic errors. Hence we find the slow-but-accurate numerical calculation preferable.…”

Section: Photon Traversementioning

confidence: 99%

“…Direct detections of planets (e.g., Kalas et al 2008) measure diskintegrated planetary properties; SRTC++ could be used to accurately forward-compute expected photometric behavior of such planets as a function of phase as they orbit their parent star (Cahoy et al 2010). SRTC++ might also be profitably applied to transit spectroscopy of planets (Hubbard et al 2001) -particularly those with thick and/or extended Titan-like atmospheres (Checlair et al 2016). The high slant optical depths in such cases (Fortney 2005), potentially combined with east-west and equatorpole inhomogeneities (Fortney et al 2010), lend themselves naturally to SRTC++'s explicit and accurate approach.…”

Section: Applicationmentioning

confidence: 99%

Spherical Radiative Transfer in C++ (SRTC++): A Parallel Monte Carlo Radiative Transfer Model for Titan

Barnes

MacKenzie

Young

et al. 2018

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We present a new computer program, SRTC++, to solve spatial problems associated with explorations of Saturn's moon Titan. The program implements a three-dimensional structure well-suited to addressing shortcomings arising from plane-parallel radiative transfer approaches. SRTC++'s design uses parallel processing in an object-oriented, compiled computer language (C++) leading to a flexible and fast architecture. We validate SRTC++ using analytical results, semianalytical radiative transfer expressions, and an existing Titan plane-parallel model. SRTC++ complements existing approaches, addressing spatial problems like near-limb and near-terminator geometries, non-Lambertian surface phase functions (including specular reflections), and surface albedo nonuniformity.

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“…Because of the tangential optical paths of transit geometry, even tenuous clouds/haze can contribute to a considerable optical depth, and, if present at low pressure, the molecular features can be significantly weakened. While they can be inconvenient obstacles to detections of molecular features, these may also be seen as a signal that could provide insights into the atmospheric compositions ( e.g., Hu et al, 2013 ; Checlair et al, 2016 ) and have even been proposed as potential biosignatures in certain atmospheric contexts (Arney et al, 2016 ). At longer wavelengths, transmission spectra are less sensitive to high-altitude haze particles due to the reduced extinction efficiency ( e.g., Hu et al, 2013 ; Arney et al, 2016 ).…”

Section: Characterizing Transiting Planetsmentioning

confidence: 99%

Exoplanet Biosignatures: Observational Prospects

et al. 2018

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Exoplanet hunting efforts have revealed the prevalence of exotic worlds with diverse properties, including Earth-sized bodies, which has fueled our endeavor to search for life beyond the Solar System. Accumulating experiences in astrophysical, chemical, and climatological characterization of uninhabitable planets are paving the way to characterization of potentially habitable planets. In this paper, we review our possibilities and limitations in characterizing temperate terrestrial planets with future observational capabilities through the 2030s and beyond, as a basis of a broad range of discussions on how to advance “astrobiology” with exoplanets. We discuss the observability of not only the proposed biosignature candidates themselves but also of more general planetary properties that provide circumstantial evidence, since the evaluation of any biosignature candidate relies on its context. Characterization of temperate Earth-sized planets in the coming years will focus on those around nearby late-type stars. The James Webb Space Telescope (JWST) and later 30-meter-class ground-based telescopes will empower their chemical investigations. Spectroscopic studies of potentially habitable planets around solar-type stars will likely require a designated spacecraft mission for direct imaging, leveraging technologies that are already being developed and tested as part of the Wide Field InfraRed Survey Telescope (WFIRST) mission. Successful initial characterization of a few nearby targets will be an important touchstone toward a more detailed scrutiny and a larger survey that are envisioned beyond 2030. The broad outlook this paper presents may help develop new observational techniques to detect relevant features as well as frameworks to diagnose planets based on the observables. Key Words: Exoplanets—Biosignatures—Characterization—Planetary atmospheres—Planetary surfaces. Astrobiology 18, 739–778.

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Titan-like exoplanets: Variations in geometric albedo and effective transit height with haze production rate

Cited by 9 publications

References 49 publications

Atmospheric Circulation, Chemistry, and Infrared Spectra of Titan-like Exoplanets around Different Stellar Types

Atmospheric Circulation, Chemistry, and Infrared Spectra of Titan-like Exoplanets around Different Stellar Types

Spherical Radiative Transfer in C++ (SRTC++): A Parallel Monte Carlo Radiative Transfer Model for Titan

Exoplanet Biosignatures: Observational Prospects

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