Developments in the Detection and Characterization of Planetary Atmospheres

The study of minor chemical species in terrestrial planets’ atmospheres can teach us about the chemistry, dynamics and evolution of the atmospheres through time. Phosphine or methane on terrestrial planets are potential biosignatures, such that their detection may signify the presence of life on a planet. Therefore, the search for these species in the solar system is an important step for the subsequent application of the same techniques to exoplanetary atmospheres. To study atmospheric depletion and the evolution of water abundance in the atmospheres of terrestrial planets, the estimation of the D/H ratio and its spatial and temporal variability is used. We used the Planetary Spectrum Generator (PSG), a radiative transfer suite, with the goal of simulating spectra from observations of Venus, Mars and Jupiter, searching for minor chemical species. The present study contributes to highlight that the PSG is an efficient tool for studying minor chemical species and compounds of astrobiological interest in planetary atmospheres, allowing to perform the detection and retrieval of the relevant molecular species. Regarding detection, it is effective in disentangling different molecular opacities affecting observations. In order to contribute to the scientific community that is focused on the study of minor chemical species in the solar system’s atmospheres, using this tool, in this work, we present the results from an analysis of observations of Venus, Mars and Jupiter, by comparison of observations with simulations in the infrared (IR). The first step was to clearly identify the position of molecular features using our model simulations, since the molecular absorption/emission features of different molecules tend to overlap. For this step, we used the method of the variation of abundances. The second step was to determine the molecular abundances and compare them with values from the literature using the retrieval method and the line depth ratio method. For Venus, our study of ${\mathrm{SO}}_2$-related observations by the Texas Echelon Cross Echelle Spectrograph (TEXES) at 7.4 $\mathsf{\mu }$m enabled the identification of absorption lines due to sulphur dioxide and carbon dioxide as well as constrain the abundance of ${\mathrm{SO}}_2$ at the cloud top. Phosphine was not detected in the comparison between the simulation and TEXES IR observations around 10.5 $\mathsf{\mu }$m. For Mars, both a positive and a non-detection of methane were studied using PSG simulations. The related spectra observations in the IR, at approximately 3.3 $\mathsf{\mu }$m, correspond, respectively, to the Mars Express (MEx) and ExoMars space probes. Moreover, an estimate of the deuterium-to-hydrogen ratio (D/H ratio) was obtained by comparing the simulations with observations by the Echelon Cross Echelle Spectrograph (EXES) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) at approximately 7.19–7.23 $\mathsf{\mu }$m. For Jupiter, the detection of ammonia, phosphine, deuterated methane and methane was studied, by comparing the simulations with IR observations by the Infrared Space Observatory (ISO) at approximately 7–12 $\mathsf{\mu }$m. Moreover, the retrieval of the profiles of ammonia and phosphine was performed. Full article

Firstly identified in images from JAXA’s orbiter Akatsuki, the cloud discontinuity of Venus is a planetary-scale phenomenon known to be recurrent since, at least, the 1980s. Interpreted as a new type of Kelvin wave, this disruption is associated to dramatic changes in the clouds’ opacity and distribution of aerosols, and it may constitute a critical piece for our understanding of the thermal balance and atmospheric circulation of Venus. Here, we report its reappearance on the dayside middle clouds four years after its last detection with Akatsuki/IR1, and for the first time, we characterize its main properties using exclusively near-infrared images from amateur observations. In agreement with previous reports, the discontinuity exhibited temporal variations in its zonal speed, orientation, length, and its effect over the clouds’ albedo during the 2019/2020 eastern elongation. Finally, a comparison with simultaneous observations by Akatsuki UVI and LIR confirmed that the discontinuity is not visible on the upper clouds’ albedo or thermal emission, while zonal speeds are slower than winds at the clouds’ top and faster than at the middle clouds, evidencing that this Kelvin wave might be transporting momentum up to upper clouds. Full article

At the cloud top of the Venus atmosphere, equatorial Kelvin waves have been observed and are considered to play an important role in the super-rotation. We were able to reproduce the wave in a general circulation model (GCM) by conducting an observing system simulation experiment (OSSE) with the help of a data assimilation system. The synthetic horizontal winds of the Kelvin wave produced by the linear wave propagating model are assimilated at the cloud top (~70 km) in realistic conditions, assuming they are obtained from cloud tracking of ultra-violet images (UVI) taken by the Venus orbiters. It is demonstrated using Eliassen–Palm (EP) fluxes that the reproduced Kelvin wave transports angular momentum and plays an important role in the magnitude and structure of the super-rotation, causing the acceleration and deceleration of zonal wind of ~0.1 m/s day⁻¹. The conditions required in order to reproduce the Kelvin wave have also been investigated. It is desirable to have 24 hourly dayside satellite observations in an equatorial orbit, such as the Akatsuki Venus climate orbiter. The results of this type of data assimilation study will be useful in the planning of future observation missions to the atmospheres of planets. Full article

The Eyjafjallajökull volcanic ash crisis in 2010 temporarily suspended European air traffic operations, as the 39-day eruption caused widely dispersed ashes to enter the lower atmosphere. In this paper, we assessed the effects of this event on the ionosphere layer and, consequently, on GPS positioning. We collected and analysed the data from four IGS stations, nearest to the volcano, for the month of April 2010. We recorded Vertical Total Electron Content (VTEC) time series, analysed their dynamics, and compared them with the GPS positioning errors of a commercial-grade, un-aided, single-frequency GPS receiver (simulating the response of a mass-market GPS receiver). The geomagnetic indices during the time period show little geomagnetic disturbance, especially during the volcanic event. Our results show an enhancement in ionosphere error by up to 15% during the volcanic ash event and an enhanced variance in GPS position components errors. This study reveals the potential impact of the charged volcanic ash on single-frequency, unaided GPS positioning accuracy in the Adriatic Sea region and establishes a foundation for studying similar events in future. Full article