Detectability of Biosignatures in Anoxic Atmospheres with the James Webb Space Telescope: A TRAPPIST-1e Case Study

Krissansen‐Totton, Joshua; Garland, Ryan; Irwin, Patrick; Catling, David C.

doi:10.3847/1538-3881/aad564

Cited by 146 publications

(164 citation statements)

References 70 publications

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“…We used Pan-dExo (Batalha et al 2017) to generate the wavelength grid and noise for the NIRSpec Prism (0.6 -5.3 µm), NIRSpec G395M (2.87 -5.10 µm), NIRSpec G235M (1.66 -3.07 µm) and NIRSpec G140M (0.97 -1.84 µm), this is done for the integration time of the secondary eclipse of WASP-43b. For the NIRSpec Prism (nominal resolving power ∼100) we use the resolution of the largest bin step as shown in Krissansen-Totton et al (2018) and for the different NIRSpec gratings (nominal resolving power ∼1000) we use a resolution of R=100.…”

Section: Application To Nirspecmentioning

confidence: 99%

Understanding and mitigating biases when studying inhomogeneous emission spectra with JWST

Taylor

Parmentier

Irwin

et al. 2020

Monthly Notices of the Royal Astronomical Society

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104

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Exoplanet emission spectra are often modelled assuming that the hemisphere observed is well represented by a horizontally homogenised atmosphere. However this approximation will likely fail for planets with a large temperature contrast in the James Webb Space Telescope (JWST) era, potentially leading to erroneous interpretations of spectra.We first develop an analytic formulation to quantify the signal-to-noise ratio and wavelength coverage necessary to disentangle temperature inhomogeneities from a hemispherically averaged spectrum. We find that for a given signal-to-noise ratio, observations at shorter wavelengths are better at detecting the presence of inhomogeneities. We then determine why the presence of an inhomogeneous thermal structure can lead to spurious molecular detections when assuming a fully homogenised planet in the retrieval process.Finally, we quantify more precisely the potential biases by modelling a suite of hot Jupiter spectra, varying the spatial contributions of a hot and a cold region, as would be observed by the different instruments of JWST/NIRSpec. We then retrieve the abundances and temperature profiles from the synthetic observations. We find that in most cases, assuming a homogeneous thermal structure when retrieving the atmospheric chemistry leads to biased results, and spurious molecular detection. Explicitly modelling the data using two profiles avoids these biases, and is statistically supported provided the wavelength coverage is wide enough, and crucially also spanning shorter wavelengths. For the high contrast used here, a single profile with a dilution factor performs as well as the two-profile case, with only one additional parameter compared to the 1-D approach.

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Section: Application To Nirspecmentioning

confidence: 99%

Understanding and mitigating biases when studying inhomogeneous emission spectra with JWST

Taylor

Parmentier

Irwin

et al. 2020

Monthly Notices of the Royal Astronomical Society

Self Cite

104

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“…We acknowledge, up front, that this may not be a physically plausible scenario due to the vastly different incident spectral energy distribution. However, given the overwhelming number of unknowns involved in self-consistent planetary atmosphere modeling (e.g., star-planet interactions, surface fluxes, formation conditions, bulk elemental composition, 3D atmospheric dynamical effects, cloud micro-physics, dynamical evolution/history) we simply choose to treat our atmosphere as "Earth-like" (as has also been done in previous works, Morley et al (2017); Krissansen-Totton et al (2018)).…”

Section: Transmission Forward Modelmentioning

confidence: 99%

“…Utilizing a combination of NIR-Spec PRISM and MIRI-LRS, they conclude that O 3 , at Earth-like abundances, would be detectable on planets 1c and 1d with 30 transits on each instrument. Also utilizing an atmospheric retrieval analysis, Krissansen-Totton et al (2018) analyzed the detectability of the CO 2 +CH 4 disequilibrium biosignature, suspected to have been present in Earth's early atmosphere when the abundances of each were significantly enhanced compared to modern-day values.…”

Section: Introductionmentioning

confidence: 99%

The Detectability and Constraints of Biosignature Gases in the Near- and Mid-infrared from Transit Transmission Spectroscopy

Tremblay

Line

Stevenson

et al. 2020

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The James Webb Space Telescope (JWST ) is expected to revolutionize our understanding of Jovian worlds over the coming decade. However, as we push towards characterizing cooler, smaller, "terrestrial-like" planets, dedicated next-generation facilities will be required to tease out the small spectral signatures indicative of biological activity. Here, we evaluate the feasibility of determining atmospheric properties, from near-to-mid-infrared transmission spectra, of transiting temperate terrestrial M-dwarf companions. Specifically, we utilize atmospheric retrievals to explore the trade space between spectral resolution, wavelength coverage, and signal-to-noise on our ability to both detect molecular species and constrain their abundances. We find that increasing spectral resolution beyond R=100 for near-infrared wavelengths, shorter than 5µm, proves to reduce the degeneracy between spectral features of different molecules and thus greatly benefits the abundance constraints. However, this benefit is greatly diminished beyond 5µm as any overlap between broad features in the mid-infrared does not deconvolve with higher resolutions. Additionally, our findings revealed that the inclusion of features beyond 11µm did not meaningfully improve the detection significance nor abundance constraints results. We conclude that an instrument with continuous wavelength coverage from ∼2-11µm, spectral resolution of R 50-300, and a 25m 2 collecting area, would be capable of detecting H 2 O, CO 2 , CH 4 , O 3 , and N 2 O in the atmosphere of an Earth-analog transiting a M-dwarf (mag K = 8.0) within 50 transits, and obtain better than an order-of-magnitude constraint on each of their abundances.

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“…We also expect to be able to determine atmospheric properties of smaller rocky planets orbiting M-dwarf host stars. It may in certain cases be possible to detect atmospheric biosignatures, but this will be challenging for JWST (Krissansen-Totton et al 2018;Lustig-Yaeger et al 2019). Unfortunately the characterization of the atmosphere of an Earth-like planet around a Sun-like star will be beyond the reach of JWST.…”

Section: Rv Observations To Better Determine the Planet Massesmentioning

confidence: 99%

A Framework For Optimizing Exoplanet Target Selection For The James Webb Space Telescope

Fortenbach¹,

Dressing

2020

PASP

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The James Webb Space Telescope (JWST) will devote significant observing time to the study of exoplanets. It will not be serviceable as was the Hubble Space Telescope, and therefore the spacecraft/instruments will have a relatively limited life. It is important to get as much science as possible out of this limited observing time. We provide an analysis framework (including publicly released computational tools) that can be used to optimize lists of exoplanet targets for atmospheric characterization. Our tools take catalogs of planet detections, either simulated, or actual; categorize the targets by planet radius and equilibrium temperature; estimate planet masses; generate model spectra and simulated instrument spectra; perform a statistical analysis to determine if the instrument spectra can confirm an atmospheric detection; and finally, rank the targets within each category by observation time required. For a catalog of simulated Transiting Exoplanet Survey Satellite planet detections, we determine an optimal target ranking for the observing time available. Our results are generally consistent with other recent studies of JWST exoplanet target optimization. We show that assumptions about target planet atmospheric metallicity, instrument performance (especially the noise floor), and statistical detection threshold, can have a significant effect on target ranking. Over its full 10-year (fuel-limited) mission, JWST has the potential to increase the number of atmospheres characterized by transmission spectroscopy by an order of magnitude (from about 50 currently to between 400 and 500).

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Detectability of Biosignatures in Anoxic Atmospheres with the James Webb Space Telescope: A TRAPPIST-1e Case Study

Cited by 146 publications

References 70 publications

Understanding and mitigating biases when studying inhomogeneous emission spectra with JWST

Understanding and mitigating biases when studying inhomogeneous emission spectra with JWST

The Detectability and Constraints of Biosignature Gases in the Near- and Mid-infrared from Transit Transmission Spectroscopy

A Framework For Optimizing Exoplanet Target Selection For The James Webb Space Telescope

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