H2O abundances and cloud properties in ten hot giant exoplanets

By Arazi Pinhas, N. Madhusudhan, S. Gandhi, R. MacDonald. Monthly notices of the Royal Astronomical Society, 2018

163 citations recorded by the source corpus.

Transmission spectroscopy of exoplanets has the potential to provide precise measurements of atmospheric chemical abundances, in particular of hot Jupiters whose large sizes and high temperatures make them conducive to such observations. To date, several transmission spectra of hot Jupiters have revealed low amplitude features of water vapour compared to expectations from cloud-free atmospheres of solar metallicity. The low spectral amplitudes in such atmospheres could either be due to the presence of aerosols that obscure part of the atmosphere or due to inherently low abundances of H$_2$O in the atmospheres. A recent survey of transmission spectra of ten hot Jupiters used empirical metrics to suggest atmospheres with a range of cloud/haze properties but with no evidence for H$_2$O depletion. Here, we conduct a detailed and homogeneous atmospheric retrieval analysis of the entire sample and report the H$_2$O abundances, cloud properties, terminator temperature profiles, and detection significances of the chemical species. Our present study finds that the majority of hot Jupiters have atmospheres consistent with sub-solar H$_2$O abundances at their day-night terminators. The best constrained abundances range from $\mathrm{log(H_2O)}$ of $-5.04^{+0.46}_{-0.30}$ to $-3.16^{+0.66}_{-0.69}$, which compared to expectations from solar-abundance equilibrium chemistry correspond to $0.018^{+0.035}_{-0.009}\times$ solar to $1.40^{+4.97}_{-1.11}\times$ solar. Besides H$_2$O we report statistical constraints on other chemical species and cloud/haze properties, including cloud/haze coverage fractions which range from $0.18^{+0.26}_{-0.12}$ to $0.76^{+0.13}_{-0.15}$. The retrieved H$_2$O abundances suggest sub-solar oxygen and/or super-solar C/O ratios, and can provide important constraints on the formation and migration pathways of hot giant exoplanets.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/ba12ef682006759906dee91a9d5c84c0aa3ecd8f

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Spectroscopy

Citations in the corpus

Mass–Metallicity Trends in Transiting Exoplanets from Atmospheric Abundances of H2O, Na, and K (2019, methodology): “We follow the retrieval approach in Welbanks & Madhusudhan (2019) based on the AURA retrieval code (Pinhas et al. 2018).”
Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects (2019, methodology): “On the other hand, the lowtemperature super-Earths and Neptunes have mostly shown flat spectra in the WFC3 bandpass (131, 124) with a few exceptions (85, 277), which indicate the predominance of clouds in low-temperature atmospheres.”
Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e (2020, background): “…have been included in retrievals of transmission spectra of exoplanets (see MacDonald & Madhusudhan 2017; Fisher & Heng 2018; Tsiaras et al. 2018; Pinhas et al. 2019; Barstow 2020, for some recent examples), cloudy retrievals are still a comparatively novel approach for self-luminous targets.”