Exoplanet atmospheres

Abstract:

The aerosol scheme for Jupiter’s upper hazes and clouds is still debated to this day, for the Crème Brûlée aerosol scheme has trouble in fitting some specific Jovian atmospheric features (Braude et al., 2020; Dahl et al., 2021). We analyse observations of Jupiter acquired with CARMENES in 2019, from visible to near infrared (0.52–1.71μm), to test three competing aerosols schemes. These observations are unique due to their spectral coverage with both high spatial and spectral resolutions, paving the way for future observations of Solar System objects. We used a model with two blue wavelength attenuating hazes (chromophores) by Anguiano-Arteaga et al., (2021); Anguiano-Arteaga et al., (2023), a model that has a single blue attenuating haze by Braude et al., (2020) and a model where the blue attenuating haze is physically constrained in a thin layer (“Crème Brûlée model”) with a more up to date parameter values from Pérez-Hoyos et al., (2020). We grouped the observations into 5 regions of the atmosphere of Jupiter and performed a Minnaert limb-darkening approximation, producing synthetic spectra at 0° and 61.45° zenith angles for each. We found that the properties of the highest aerosol layer dominate the fit to the observations, with particle size (Models A and B) and cloud base abundance (Models A and C) being the most influential parameters. We found that the extended chromophore model from Braude et al., (2020) fits the observations better than the other two models. However, none of the tested schemes fully reproduce the data, as all yield X²/N_free values greater than unity, indicating limitations in the current aerosol parametrisations. These results suggest that a consistent characterisation of Jovian aerosols requires models constrained by a broader spectral range, including ultraviolet observations sensitive to chromophore absorption and thermal infrared data probing deeper cloud layers.

Abstract:

The spectrum of an exoplanet reveals the physical, chemical, and biological processes that have shaped its history and govern its future. However, observations of exoplanet spectra are complicated by the overwhelming glare of their host stars. Here, we focus on high-resolution spectroscopy (HRS) (R∼5,000−140,000), which helps disentangle and isolate the exoplanet’s spectrum. HRS resolves molecular features into a dense forest of individual lines in a pattern that is unique for a given molecule. For close-in planets, the spectral lines undergo large Doppler shifts during the planet’s orbit, while the host star and Earth’s spectral features remain essentially stationary, enabling a velocity separation of the planet. For slower-moving, wide-orbit planets, HRS, aided by high contrast imaging, instead isolates their spectra using their spatial separation (high contrast spectroscopy; HCS). The planet’s spectral lines are compared with HRS model atmospheric spectra, typically using cross-correlation to sum their signals. It is essentially a form of fingerprinting for exoplanet atmospheres and works for both transiting and non-transiting planets. It measures their orbital velocity, true mass, and simultaneously characterizes their atmosphere. The unique sensitivity of HRS to the depth, shape, and position of the planet’s spectral lines allows it to measure atmospheric composition, structure, clouds, and dynamics, including day-to-night winds and equatorial jets, plus its rotation period and even its magnetic field. These are extracted using statistically robust log-likelihood frameworks and match space-based instruments in their precision. This chapter describes the HRS technique in detail and concludes with future prospects with Extremely Large Telescopes to identify biosignatures on nearby rocky worlds and map features in the atmospheres of giant exoplanets.

Abstract:

Close-in exoplanets are tidally locked to their host star and thus exhibit extreme atmospheric temperature gradients. It has been theorized that the fraction of star light absorbed by such planets during transit changes as a function of orbital phase as progressively hotter or colder atmospheric gas rotates into view, but this effect has not been observed so far. Here we show that two transits of the ultrahot Jupiter WASP-121 b, acquired with JWST/NIRSpec and NIRISS, exhibit asymmetric light curves caused by the planet’s rotation during transit. We observe increasing CO absorption and slightly decreasing H2O absorption in the transmission spectrum as the planet rotates. These results are indicative of a stronger longitudinal temperature gradient across the evening than across the morning terminator, consistent with higher temperatures in the eastern half than in the western half of the dayside. The observed changes of the transmission spectrum with orbital phase are in line with the temperature increase causing thermal dissociation of H2O, while CO remains abundant. The observation of longitudinal gradients in atmospheric temperature and chemistry from the planet’s rotational transit provides a new probe for constraining atmospheric heterogeneity using JWST beyond differences between morning and evening terminators from limb asymmetries.

Abstract: