Fundamental Challenges to Remote Sensing of Exo-Earths

Paradise, Adiv; Menou, Kristen; Lee, Christopher; Fan, Bo Lin

doi:10.48550/arxiv.2106.00079

Cited by 3 publications

(3 citation statements)

References 48 publications

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“…They remarked that longer, continuous observing periods will help with mapping. Indeed, clouds may have the largest impact on spectra variation (Paradise et al 2021), as we have also found in our simualtions. Additionally, Schwartz et al (2016) found that, at least theoretically, it should be possible to determine the obliquity of an exoplanet by observing at 2-4 different orbital phases.…”

Section: Challenges and Future Worksupporting

confidence: 83%

Variability due to climate and chemistry in observations of oxygenated Earth-analogue exoplanets

Cooke¹,

Marsh²,

Walsh³

et al. 2022

Preprint

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The Great Oxidation Event was a period during which Earth's atmospheric oxygen (O 2 ) concentrations increased from ∼ 10 −5 times its present atmospheric level (PAL) to near modern levels, marking the start of the Proterozoic geological eon 2.4 billion years ago. Using WACCM6, an Earth System Model, we simulate the atmosphere of Earth-analogue exoplanets with O 2 mixing ratios between 0.1% and 150% PAL. Using these simulations, we calculate the reflection/emission spectra over multiple orbits using the Planetary Spectrum Generator. We highlight how observer angle, albedo, chemistry, and clouds affect the simulated observations. We show that inter-annual climate variations, as well short-term variations due to clouds, can be observed in our simulated atmospheres with a telescope concept such as LUVOIR or HabEx. Annual variability and seasonal variability can change the planet's reflected flux (including the reflected flux of key spectral features such as O 2 and H 2 O) by up to factors of 5 and 20, respectively, for the same orbital phase. This variability is best observed with a highthroughput coronagraph. For example, HabEx (4 m) with a starshade performs up to a factor of two times better than a LUVOIR B (6 m) style telescope. The variability and signal-to-noise ratio of some spectral features depends non-linearly on atmospheric O 2 concentration. This is caused by temperature and chemical column depth variations, as well as generally increased liquid and ice cloud content for atmospheres with O 2 concentrations of <1% PAL.

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Section: Challenges and Future Worksupporting

confidence: 83%

Variability due to climate and chemistry in observations of oxygenated Earth-analogue exoplanets

Cooke¹,

Marsh²,

Walsh³

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…Proposed next-generation direct imaging missions might be capable of enough precision for the exo-cartography of small planets-solving the inverse problem of 2D albedo distributions from time-resolved light curves-which might discriminate between land and ocean surfaces (Cowan & Fujii 2018;Farr et al 2018;Lustig-Yaeger et al 2018;Aizawa et al 2020;Kawahara 2020). Interpretations of the data may remain highly model dependent and burdened by cloud removal, however (Paradise et al 2021;Teinturier et al 2022). Ocean fractions might also be discerned from near-infrared polarimetric observations (Takahashi et al 2021).…”

Section: Constraints From Astrophysical Datamentioning

confidence: 99%

Blue Marble, Stagnant Lid: Could Dynamic Topography Avert a Waterworld?

2022

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Topography on a wet rocky exoplanet could raise land above its sea level. Although land elevation is the product of many complex processes, the large-scale topographic features on any geodynamically active planet are the expression of the convecting mantle beneath the surface. This so-called “dynamic topography” exists regardless of a planet’s tectonic regime or volcanism; its amplitude, with a few assumptions, can be estimated via numerical simulations of convection as a function of the mantle Rayleigh number. We develop new scaling relationships for dynamic topography on stagnant lid planets using 2D convection models with temperature-dependent viscosity. These scalings are applied to 1D thermal history models to explore how dynamic topography varies with exoplanetary observables over a wide parameter space. Dynamic topography amplitudes are converted to an ocean basin capacity, the minimum water volume required to flood the entire surface. Basin capacity increases less steeply with planet mass than does the amount of water itself, assuming a water inventory that is a constant planetary mass fraction. We find that dynamically supported topography alone could be sufficient to maintain subaerial land on Earth-size stagnant lid planets with surface water inventories of up to approximately 10−4 times their mass, in the most favorable thermal states. By considering only dynamic topography, which has ∼1 km amplitudes on Earth, these results represent a lower limit to the true ocean basin capacity. Our work indicates that deterministic geophysical modeling could inform the variability of land propensity on low-mass planets.

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“…Proposed next-generation direct imaging missions might be capable of enough precision for the exo-cartography of small planetssolving the inverse problem of 2D albedo distributions from time-resolved light-curves-which might discrim-inate between land and ocean surfaces (Cowan & Fujii 2018;Farr et al 2018;Lustig-Yaeger et al 2018;Kawahara 2020;Aizawa et al 2020). Interpretations of the data may remain highly model-dependent and burdened by cloud removal, however (Paradise et al 2021;Teinturier et al 2022). Ocean fractions might also be discerned from near-infrared polarimetric observations (Takahashi et al 2021).…”

Section: Constraints From Astrophysical Datamentioning

confidence: 99%

Blue marble, stagnant lid: Could dynamic topography avert a waterworld?

Guimond,

Rudge,

Shorttle

2022

Preprint

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Topography on a wet rocky exoplanet could raise land above its sea level. Although land elevation is the product of many complex processes, the large-scale topographic features on any geodynamicallyactive planet are the expression of the convecting mantle beneath the surface. This so-called "dynamic topography" exists regardless of a planet's tectonic regime or volcanism; its amplitude, with a few assumptions, can be estimated via numerical simulations of convection as a function of the mantle Rayleigh number. We develop new scaling relationships for dynamic topography on stagnant lid planets using 2D convection models with temperature-dependent viscosity. These scalings are applied to 1D thermal history models to explore how dynamic topography varies with exoplanetary observables over a wide parameter space. Dynamic topography amplitudes are converted to an ocean basin capacity, the minimum water volume required to flood the entire surface. Basin capacity increases less steeply with planet mass than does the amount of water itself, assuming a water inventory that is a constant planetary mass fraction. We find that dynamically-supported topography alone could be sufficient to maintain subaerial land on Earth-size stagnant lid planets with surface water inventories of up to approximately 10 −4 times their mass, in the most favourable thermal states. By considering only dynamic topography, which has ∼1-km amplitudes on Earth, these results represent a lower limit to the true ocean basin capacity. Our work indicates that deterministic geophysical modelling could inform the variability of land propensity on low-mass planets.

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Fundamental Challenges to Remote Sensing of Exo-Earths

Cited by 3 publications

References 48 publications

Variability due to climate and chemistry in observations of oxygenated Earth-analogue exoplanets

Variability due to climate and chemistry in observations of oxygenated Earth-analogue exoplanets

Blue Marble, Stagnant Lid: Could Dynamic Topography Avert a Waterworld?

Blue marble, stagnant lid: Could dynamic topography avert a waterworld?

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