Are your spectroscopic data being used?

Keyte

Waldmann

et al. 2020

ApJ

In current models used to interpret exoplanet atmospheric observations, the planetary mass is treated as a prior and is measured/estimated independently with external methods, such as radial velocity or transit timing variation techniques. This approach is necessary as available spectroscopic data do not have sufficient wavelength coverage and/or signal-to-noise to infer the planetary mass. We examine here whether the planetary mass can be directly retrieved from transit spectra as observed by future space observatories, which will provide higher quality spectra. More in general, we quantify the impact of mass uncertainties on spectral retrieval analyses for a host of atmospheric scenarios. Our approach is both analytical and numerical: we first use simple approximations to extract analytically the influence of each atmospheric/planetary parameter to the wavelength-dependent transit depth. We then adopt a fully Bayesian retrieval model to quantify the propagation of the mass uncertainty onto other atmospheric parameters. We found that for clear-sky, gaseous atmospheres the posterior distributions are the same when the mass is known or retrieved. The retrieved mass is very accurate, with a precision of more than 10%, provided the wavelength coverage and signal-to-noise ratio are adequate. When opaque clouds are included in the simulations, the uncertainties in the retrieved mass increase, especially for high altitude clouds. However, atmospheric parameters such as the temperature and trace-gas abundances are unaffected by the knowledge of the mass. Secondary atmospheres, expected to be present in many super-Earths, are more challenging due to the higher degree of freedom for the atmospheric main component, which is unknown. For broad wavelength range and adequate signal-to-noise observations, the mass can still be retrieved accurately and precisely if clouds are not present, and so are all the other atmospheric/planetary parameters. When clouds are added, we find that the mass uncertainties may impact substantially the retrieval of the mean molecular weight: an independent characterization of the mass would therefore be helpful to capture/confirm the main atmospheric constituent.

Section: Methodsmentioning

confidence: 99%

Impact of Planetary Mass Uncertainties on Exoplanet Atmospheric Retrievals

Keyte

Waldmann

et al. 2020

ApJ

“…Because clouds are most constrained by the transmission spectrum, we model them with a fully opaque cloud layer above a given pressure, restricted to the day-and night-side regions. For the chemistry, we use the molecular line lists from the Exomol project (Tennyson et al 2016(Tennyson et al , 2020Chubb et al 2021), HITEMP (Rothman & Gordon 2014), and HITRAN (Gordon et al 2016) (Li et al 2015), CO 2 (Rothman et al 2010), C 2 H 2 (Wilzewski et al 2016), C 2 H 4 (Mant et al 2018), NH 3 (Yurchenko et al 2011), andHCN (Harris et al 2006;Barber et al 2013).…”

Section: Opacity Sourcesmentioning

confidence: 99%

An Exploration of Model Degeneracies with a Unified Phase Curve Retrieval Analysis: The Light and Dark Sides of WASP-43 b

Al-Refaie

Edwards

et al. 2021

ApJ

The analysis of exoplanetary atmospheres often relies upon the observation of transit or eclipse events. While very powerful, these snapshots provide mainly one-dimensional information on the planet structure and do not easily allow precise latitude-longitude characterizations. The phase curve technique, which consists of measuring the planet emission throughout its entire orbit, can break this limitation and provide useful two-dimensional thermal and chemical constraints on the atmosphere. As of today, however, computing performances have limited our ability to perform unified retrieval studies on the full set of observed spectra from phase curve observations at the same time. Here, we present a new phase curve model that enables fast, unified retrieval capabilities. We apply our technique to the combined phase curve data from the Hubble and Spitzer space telescopes of the hot Jupiter WASP-43 b. We tested different scenarios and discussed the dependence of our solution on different assumptions in the model. Our more comprehensive approach suggests that multiple interpretations of this data set are possible, but our more complex model is consistent with the presence of thermal inversions and a metal-rich atmosphere, contrasting with previous data analyses, although this likely depends on the Spitzer data reduction. The detailed constraints extracted here demonstrate the importance of developing and understanding advanced phase curve techniques, which we believe will unlock access to a richer picture of exoplanet atmospheres.

“…The retrieval of the transmission spectra was performed using the publicly available retrieval suite TauREx 3 (Al-Refaie et al 2019). 6 We included the molecular opacities from the ExoMol database (Tennyson et al 2016), the high-resolution transmission molecular absorption database (HITRAN; Gordon et al 2016), and the the high-temperature molecular spectroscopic database (HITEMP; Rothman et al 2010) (Yurchenko & Tennyson 2014), CO (Li et al 2015), CO 2 (Rothman et al 2010), and NH 3 (Yurchenko et al 2011). On top of this, we also included collision-induced absorption (CIA) from H 2 -H 2 (Abel et al 2011;Fletcher et al 2018) and H 2 -He (Abel et al 2012) as well as Rayleigh scattering for all molecules.…”

Section: Atmospheric Modelingmentioning

confidence: 99%

Hubble WFC3 Spectroscopy of the Habitable-zone Super-Earth LHS 1140 b

Edwards

Mori

et al. 2020

Atmospheric characterization of temperate, rocky planets is the holy grail of exoplanet studies. These worlds are at the limits of our capabilities with current instrumentation in transmission spectroscopy and challenge our state-ofthe-art statistical techniques. Here we present the transmission spectrum of the temperate super-Earth LHS 1140b using the Hubble Space Telescope (HST). The Wide Field Camera 3 (WFC3) G141 grism data of this habitablezone (T eq =235 K) super-Earth (R=1.7 R ⊕ ) shows tentative evidence of water. However, the signal-to-noise ratio, and thus the significance of the detection, is low and stellar contamination models can cause modulation over the spectral band probed. We attempt to correct for contamination using these models and find that, while many still lead to evidence for water, some could provide reasonable fits to the data without the need for molecular absorption although most of these cause features in the visible ground-based data which are nonphysical. Future observations with the James Webb Space Telescope would be capable of confirming, or refuting, this atmospheric detection.