Aerosols in Exoplanet Atmospheres

Gao, Peter; Wakeford, Hannah R.; Moran, Sarah E.; Parmentier, Vivien

doi:10.48550/arxiv.2102.03480

Cited by 3 publications

(4 citation statements)

References 350 publications

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Section: Iron-rich Silicatesmentioning

confidence: 99%

“…Standard brown dwarf cloudy models include iron droplets, but recent microphysical studies have shown that iron clouds do not readily form (Gao et al 2021). Iron has a higher surface energy that creates a nucleation energy barrier preventing cloud formation (Gao et al 2021). However, FeH disappears from the spectra of late L-dwarfs (Kirkpatrick 2005) suggesting that iron is indeed removed from the gas phase.…”

Section: Iron-rich Silicatesmentioning

confidence: 99%

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Empirically Determining Substellar Cloud Compositions in the era of JWST

Luna,

Morley

2021

Preprint

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Most brown dwarfs have atmospheres with temperatures cold enough to form clouds. A variety of materials likely condense, including refractory metal oxides and silicates; the precise compositions and crystal structures of predicted cloud particles depend on the modeling framework used and have not yet been empirically constrained. Spitzer has shown tentative evidence of the silicate feature in L dwarf spectra and JWST can measure these features in many L dwarfs. Here, we present new models to predict the signatures of the strongest cloud absorption features. We investigate different cloud mineral species and determine how particle size, mineralogy, and crystalline structure change spectral features. We find that silicate and refractory clouds have a strong cloud absorption feature for small particle sizes (≤ 1 µm). Model spectra are compared to five brown dwarfs that show evidence of the silicate feature; models that include small particles in the upper layers of the atmosphere produce a broad cloud mineral feature, and that better match the observed spectra than the Ackerman & Marley (2001) cloud model. We simulate observations with the MIRI instrument on JWST for a range of nearby, cloudy brown dwarfs, demonstrating that these features could be readily detectable if small particles are present. Furthermore, for photometrically variable brown dwarfs, our predictions suggest that with JWST, by measuring spectroscopic variability inside and outside a mineral feature, we can establish silicate (or other) clouds as the cause of variability. Mid-infrared spectroscopy is a promising tool to empirically constrain the complex cloud condensation sequence in brown dwarf atmospheres.

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Section: Iron-rich Silicatesmentioning

confidence: 99%

Section: Iron-rich Silicatesmentioning

confidence: 99%

Empirically Determining Substellar Cloud Compositions in the era of JWST

Luna,

Morley

2021

Preprint

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“…In the simulations described in this paper, the refractive indices for the water ice clouds were taken from Massie & Hervig (2013); Gordon et al (2017) while the Mie scattering implementation used was from Bohren & Huffman (1983) and used 20 angles and 200 size bins from 0.005 to 20 µm. The hypothetical effect of a haze layer was the last additional component included in the simulations, with a thin, high layer of tholin haze composed of 0.1 and 1 µm particles (particle size based on the approximate peak of a number of modeled haze particle distributions -see Figure 8 of Gao et al (2021) (specific details on haze particles used are available in the attached config files in the appendix).…”

Section: Clouds and Hazes In The υ Andromedae D Atmospherementioning

confidence: 99%

Simulating Reflected Light Exoplanet Spectra of the Promising Direct Imaging Target, $\upsilon$ Andromedae d, with a New, Fast Sampling Method Using the Planetary Spectrum Generator

Saxena,

Villanueva,

Zimmerman

et al. 2021

Preprint

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Simulations of exoplanet albedo profiles are key to planning and interpreting future direct imaging observations. In this paper we demonstrate the use of the Planetary Spectrum Generator (PSG) to produce simulations of reflected light exoplanet spectra. We use PSG to examine multiple issues relevant to all models of directly imaged exoplanet spectra and to produce sample spectra of the bright, nearby exoplanet υ Andromedae d, a potential direct imaging target for next-generation facilities. We introduce a new, fast, and accurate sub-sampling technique that enables calculations of disk-integrated spectra one order of magnitude faster than Chebyshev-Gauss sampling for moderate-to high-resolution sampling. Using this method and a first-principles-derived atmosphere for υ And d, we simulate phase-dependent spectra for a variety of different potential atmospheric configurations. The simulated spectra for υ And d include versions with different haze and cloud properties. Based on our combined analysis of this planet's orbital parameters, phase-and illumination-appropriate model spectra, and realistic instrument noise parameters, we find that υ And d is a potentially favorable direct imaging and spectroscopy target for the Coronagraph Instrument (CGI) on the Nancy Grace Roman Space Telescope. When a noise model corresponding to the Roman CGI SPC spectroscopy mode is included, PSG predicts the time required to reach a signal-to-noise ratio of 10 of the simulated spectra in both the central wavelength bin of the Roman CGI SPC spectroscopy mode (R=50 spectrum) and of the Band 1 HLC imaging mode is approximately 400 and and less than 40 hours, respectively. We also discuss potential pathways to extricating information about the planet and its atmosphere with future observations and find that Roman observations may be able to bound the interior temperature of the planet.

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“…Thus, "dust" can be replaced by "aerosols" in this paper. We note that some literature only used the "dust" to express solid particles lifted from the ground, such as the dust devil of Mars (see e.g.,Gao et al 2021).…”

mentioning

confidence: 99%

Grain Growth in Escaping Atmospheres: Implications for the Radius Inflation of Super-Puffs

Ohno,

Tanaka

2021

Preprint

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Super-puffs-low-mass exoplanets with extremely low bulk density-are attractive targets for exploring their atmospheres and formation processes. Recent studies suggested that the large radii of super-puffs may be caused by atmospheric dust entrained in the escaping atmospheres. In this study, we investigate how the dust grows in escaping atmospheres and influence the transit radii using a microphysical model of grain growth. Collision growth is efficient in many cases, leading to hinder the upward transport of dust via enhanced gravitational settling. We find that dust abundance in the outflow hardly exceeds the Mach number at the dust production region. Thus, dust formed at upper atmospheres, say P 10 −5 bar, are needed to launch a dusty outflow with high dust abundance. With sufficiently high dust production altitudes and rate, the dusty outflow can enhance the observable radius by a factor of ∼ 2 or even more. We suggest that photochemical haze is a promising candidate of high-altitude dust that can be entrained in the outflow. We also compute the synthetic transmission spectra of super-puff atmospheres and demonstrate that the dusty outflow produces a broad spectral slope and obscures molecular features, in agreement with recently reported featureless spectra. Lastly, using an interior structure model, we suggest that the atmospheric dust could drastically enhance the observable radius only for planets in a narrow mass range of ∼ 2-5M ⊕ , in which the boil-off tends to cause total atmospheric loss. This may explain why super-puffs are uncommon despite the suggested universality of photochemical hazes.

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Aerosols in Exoplanet Atmospheres

Cited by 3 publications

References 350 publications

Empirically Determining Substellar Cloud Compositions in the era of JWST

Empirically Determining Substellar Cloud Compositions in the era of JWST

Simulating Reflected Light Exoplanet Spectra of the Promising Direct Imaging Target, $\upsilon$ Andromedae d, with a New, Fast Sampling Method Using the Planetary Spectrum Generator

Grain Growth in Escaping Atmospheres: Implications for the Radius Inflation of Super-Puffs

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