Planetary atmosphere observation analysis

Abstract:

VLT/MUSE, HST/STIS and HST/WFC3 observations of Uranus in the visible/near-infrared were employed to probe spatial and temporal variability within its atmosphere. A Minnaert analysis of Uranus’ north polar hood reveals a temporal brightening of this feature, predomi- nantly caused by physical changes within the atmosphere, as opposed to any brightening effects caused by changes in viewing geometry as Uranus’ orbit progresses towards northern summer solstice in 2030. A reduction in the temporal rate of brightening was also provisionally ob- served. The holistic aerosol model [Irwin et al., 2022] was applied to latitudinal retrieval analyses on the three datasets, determining an increase in the integrated opacity (τ), and a re- duction in the imaginary refractive index spectrum (ni) longwards of 0.6 μm, of the 1 – 2-bar haze (aerosol-2) layer north of ∼40°N to be the predominant cause of the hood’s brightening. The single-scattering albedo of the aerosol-2 layer in the 60 – 70°N latitude band at 0.8 μm is observed to increase from ∼0.958 ± 0.002 in 2012, to ∼0.973 ± 0.002 in 2015, and to ∼0.9918 ± 0.0002 in 2021 from HST/STIS and VLT/MUSE retrieval analyses. Between the 2012 and 2015 STIS observations, the average increase in τ2 was 1.09 ± 0.08 at 0.8 μm, a ∼33% increase. An average increase in τ for the deep haze (aerosol-1) layer north of ∼45°N of 0.6 ± 0.1 at 0.8 μm (∼56% increase), and an average decrease in polar cloud-top methane (CH4) VMR from 40 – 80°N of 0.0019 ± 0.0003 (∼10% decrease) were also found between 2012 and 2015. A further reduction in polar cloud-top CH4 was found from analysis of the 2021 VLT/MUSE observation contrary to Sromovsky et al. [2019]’s conclusion of a general latitudinal stability. The 1 – 2-bar haze layer altitude is observed to be very stable, provid- ing evidence for it lying within a region of static stability [Irwin et al., 2022]. The results were found to be consistent with a temporal slowing of a stratospheric meridional circulation exhibiting downwelling at the poles.

Abstract:

The James Webb Space Telescope (JWST) presents the opportunity to transform our understanding of planets and the origins of life by revealing the atmospheric compositions, structures, and dynamics of transiting exoplanets in unprecedented detail. However, the high-precision, time-series observations required for such investigations have unique technical challenges, and prior experience with other facilities indicates that there will be a steep learning curve when JWST becomes operational. In this paper we describe the science objectives and detailed plans of the Transiting Exoplanet Community Early Release Science (ERS) Program, which is a recently approved program for JWST observations early in Cycle 1. The goal of this project, for which the obtained data will have no exclusive access period, is to accelerate the acquisition and diffusion of technical expertise for transiting exoplanet observations with JWST, while also providing a compelling set of representative datasets that will enable immediate scientific breakthroughs. The Transiting Exoplanet Community ERS Program will exercise the time-series modes of all four JWST instruments that have been identified as the consensus highest priorities, observe the full suite of transiting planet characterization geometries (transits, eclipses, and phase curves), and target planets with host stars that span an illustrative range of brightnesses. The observations in this program were defined through an inclusive and transparent process that had participation from JWST instrument experts and international leaders in transiting exoplanet studies. Community engagement in the project will be centered on a two-phase Data Challenge that culminates with the delivery of planetary spectra, time-series instrument performance reports, and open-source data analysis toolkits in time to inform the agenda for Cycle 2 of the JWST mission.