Characterize

 

The next step after discovering an object of astronomical interest is to initiate its study. In this quest, we work towards developing robust/reliable characterization pipelines for exoplanetary science. Theoretical works aim at supporting our community’s best use of the new James Webb Space Telescope. In parallel, applications with the Spitzer and Hubble Space Telescopes provide us with the first glimpses in the atmospheres of other worlds.

Exploring the Atmosphere of Terrestrial Planets

Terrestrial planets around Dwarf stars are uniquely suited for atmospheric exploration owing to the small size of their host. In this subquest, we leverage such optimal configuration to initiate the atmospheric characterization of new worlds.”

Showcased Papers: 

"Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1"
de Wit*, Wakeford*, Lewis*, et al. 2018

 

 

 

 

 

 

 

 

 

 

 

 

"Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets"

Bourrier, de Wit, et al. 2017

 

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Transmission spectra of TRAPPIST-1 d, e, f and g compared with synthetic atmospheres dominated by hydrogen (H2), water (H2O), carbon dioxide (CO2) and nitrogen (N2). Trace gases are given in  parentheses following the dominant gas. HST/WFC3 measurements are shown as black circles with 1σ error bars. Each spectrum is shown shifted by its average over the WFC3 band. The measurements are inconsistent with the presence of a cloud-free H2-dominated atmosphere at greater than 3σ confidence for planets d, e and f (only the values larger than 3σ are reported in the legends). Figure from de Wit, Wakeford, Lewis, et al. 2018.

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Searching for signs of exospheres around the TRAPPIST-1 planets. Ly- line proles of TRAPPIST-1. Solid-line profiles correspond to our best estimates for the theoretical intrinsic Ly-line in Visit 1-3 (blue) and in Visit 4 (black). They yield the dashed-line profiles after ISM absorption and convolution by STIS LSF. ISM absorption profile in the range 0-1 has been scaled to the vertical axis range and plotted as a dotted black line. The dashed-line profile in Visit 4 was adjusted to the observations (red histogram, equal to the average of all spectra in Visit 4) outside of the hatched regions, and excluding the variable range between -187 and -55kms^-1 (highlighted in orange).

Enabling the Reliable Decryption of Exoplanet Transmission Spectra

As we enter a new era of Space Exploration with the JWST and the ELTs, the tools we use to decrypt astronomical data need to evolve to ensure that we reliably decode new signals and do not misinterpret their groundbreaking content.

Showcased Papers: 

"The Impending Opacity Challenge in Exoplanet Atmospheric Characterization"
Niraula*, de Wit*, et al. 2022

 

 

 

 

 

 

 

 

 

 

 

 

 

 

"Constraining Exoplanet Mass from Transmission Spectroscopy"

de Wit & Seager 2013

 

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Propagation of the ensemble of opacity-model perturbations to the level of retrieved  atmospheric properties. PPDs of the retrieved atmospheric parameters (that is, final data product) for the super-Earth scenario highlighting the biases induced by perturbations to our opacity model. Each cross-section is identified by its colour and label on the right. The dotted black vertical lines represent the true values used in generating the synthetic spectrum. Deviations with a statistical significance of up to ~20σ and physical significance of over 1 dex are reported. This suggests the significant sensitivity of retrieved atmospheric properties to opacity models in upcoming atmospheric retrieval efforts. Figure from Niraula, de Wit, et al. 2022.

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Probing the information content of exoplanet transmission spectra. A line profile (fν) depends on the pressure (p) as a rational function at fixed temperature (T) and frequency (ν). (A) Dependency of fν on T and p, at fixed ν, that shows the four domains of different dependency regimes of fν on p whose boundaries are T-dependent (gray dot-dash lines). The black dot-dash lines represents the position of the slices in the {T − p − f} space used to highlight that fν behaves as a rational function of p, at {T, ν} fixed. Planels B and C present the slices at T = 1200K and T = 200K, respectively. These slices show that fν behaves as a rational function of p with a zero and a pair of conjugated zeros (Fig. S.20). In particular, the absolute value of the zero is less than the poles’, as underscored by the sequential transition from the following dependency regimes ∝ p0, ∝ p1, ∝ p∼0, and ∝ p−1 with increasing p—the dotted and the dashed lines represent a slope of 1 and 2, respectively. (D) Dependency of the absorption coefficient (αν) on p, at T = 200K. The exponent of the αν dependency on p increases by one compared to fν dependency on p. The exponent increase by one because of αν’s additional zero at p = 0 that originates from the number density.  Figure from de Wit & Seager 2013.

Towards 3D Maps of Other Worlds

Although humanity does not yet have the capabilities to spatially resolve stars other than our Sun, there exist ways to start mapping exoplanets. Using such approaches, it will be possible to study tri-dimensional structures in the atmospheres of other worlds and their evolution. Stay tune for some exo weather forecast!

Showcased Papers: 

"Inference of Inhomogneeous Clouds in an Exoplanet Atmosphere"
Demory, de Wit, et al. 2013

 

 

 

 

 

 

 

 

 

"Towards consistent mapping of distant worlds: secondary-eclipse scanning of the exoplanet HD 189733b"

de Wit et al. 2012

 

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The inhomogeneous cloud cover of Kepler-7b. Left Panel: Longitudinal brightness maps of Kepler-7b. Kepler-7b’s longitudinal brightness distributions Ip/I as retrieved in Kepler’s bandpass. Right Panel: Artistic rendering of Kepler-7b’s dayside showcasing a permanent cloud coverage on its western side. Figure from Demory, de Wit, et al. 2013.

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Schematic description of the anomalous occultation ingress/egress induced by the shape or the brightness distribution of an exoplanet. The red curve indicates the occultation photometry for a non-uniformly-bright disk (hot spot in red). The yellow curve indicates the occultation photometry for an oblate exoplanet (yellow ellipse). Both synthetic scenarios show specific deviations from the occultation photometry of uniformly-bright disk (black curve) in the occultation ingress/egress. Figure from de Wit, et al. 2012.

Know the Star, Know the Planet (In Construction)

Probing the Interior of Other Astronomical Bodies

Constraining the density of astronomical bodies is key to discussing their interior properties, and even their formation history. In this subquests, we consider the reliability of existing strategies and explore new ones.

Showcased Papers: 

"On the Effects of Planetary Oblateness on Exoplanet Studies"
Berardo & de Wit 2022

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

"Constraining the Interiors of Asteroids Through Close Encounters"

Dinsmore & de Wit 2022 (link to follow)

 

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Absence of observational constraints on oblateness limits the access to tight constraints on exoplanets’ density. The cumulative number of planets with a fractional density error below a certain value (blue line). The black lines show the percentage by which the density would change if a previously assumed spherical planet were to be oblate to a certain degree, calculated using equation 10. The red line indicating a value of f = 0.25 is in reference to the limits of current observations (pre-JWST).  Figure from Berardo & de Wit 2022.

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Background Photo Credit: NASA/JPL-Caltech/R. Hurt, T. Pyle (IPAC) 

Data, best-fitting results, and residuals for a fit to synthetic data simulated for a reference asteroid. Uncertainty bands are also shown. The best fit results are consistent with the data. Right Panel: Cross-sectional slices of the extracted uncertainty distribution on density, which is nearly identical to and statistically consistent with the true distribution for this synthetic case with a dense asymmetric core. Figure from Dinsmore & de Wit 2022.