Venus’s cloud-top superrotation, characterized by equatorial zonal winds of ~100 m/s, is sustained by the atmospheric angular momentum (AM) induced by atmospheric waves, especially thermal tides, and meridional circulation. However, the overall patterns of thermal tides and their individual components’ contribution to superrotation remain poorly understood. Recent Akatsuki observations and semispectral model simulations suggest that the semidiurnal tide is the dominant driving force behind cloud-top superrotation. Using a 16-year radio occultation dataset observed by Venus Express and Akatsuki, we have, for the first time, revealed the thermal tide structure from the cloud base to mesopause (50-90 km) in the southern hemisphere and validated the tidal patterns simulated by the Venus Planetary Climate Model. The simulation indicates that diurnal tide-induced AM flux divergence is the primary driving force for the equatorial cloud-top superrotation, contrary to the previously held belief that the semidiurnal tide was dominant.
How to cite: Lai, D., Lebonnois, S., and Li, T.: Contribution of Diurnal Tide to Venus Cloud-Top Superrotation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5337, https://doi.org/10.5194/egusphere-egu25-5337, 2025.
The atmospheric response to solar energetic particle (SEP) events has been studied in depth on Earth, but far less extensively on Mars. Understanding the Martian atmosphere's response to SEP events gives insight into how external forcing affects the photochemical balance in the Martian atmosphere. SEP events from 2004 to 2024 were identified using the error logs from Mars Express. This methodology contributed to developing a comprehensive database of confirmed space weather events on Mars. We analysed data from the spectrometers NOMAD and SPICAM onboard the ExoMars Trace Gas Orbiter and Mars Express, respectively, to study the effects of SEP events on atmospheric ozone. We observed ozone depletion during and in the days following SEP events by examining vertical profiles of ozone abundance before, during, and after SEP events. The ozone depletion typically lasted from several hours to a few days, before pre-SEP event ozone levels were reached. Ozone depletion was most significant at 35-40 km, with up to 70% depletion. Using ozone column abundance time series statistical trends derived from superposed epoch analysis of multiple SEP events revealed a strong correlation between SEP events and ozone depletion. These findings demonstrate that the Martian atmosphere is severely impacted by solar energetic events, and provide insights for improving atmospheric models.
How to cite: Haltuff, E., Knutsen, E. W., Piccialli, A., Nakamura, Y., and Thomas, I.: Ozone depletion from solar energetic particle events on Mars., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19279, https://doi.org/10.5194/egusphere-egu25-19279, 2025.
The time averaged winter polar vortex on Mars has been observed to have an annular structure, with a potential vorticity (PV) local minimum at the pole and a surrounding region of higher PV. This structure is known to be barotropically unstable; latent heat released by condensation of atmospheric CO2 is thought to be the major forcing mechanism responsible for maintaining it. Whilst the time-averaged polar vortex is seen to take a smooth annular structure, reanalysis data suggest the instantaneous polar vortex is spatially patchy with localised regions of higher and lower PV rotating around the pole. Polar vortices are typically seen to have strong mixing barriers on their equatorward edges, where large PV gradients are present, however it is not known whether this differs for a patchy polar vortex such as on Mars. Given the close correlation between PV gradients and atmospheric horizontal mixing properties, it is thought that this patchiness may have significant effects on the transport of dust and trace gases within Mars’ polar regions.
Here we present results from a novel modelling approach aiming to represent a potential driver of polar vortex patchiness and its impacts on atmospheric mixing. The shallow water equations are solved on a sphere, with additional terms representing a zonally symmetric radiative forcing, and spatially variable CO2 condensation. A new finite element model, Gusto, is used; this has the potential for future work to utilise adaptive resolution meshes. The effect of the spatially variable latent heating representation is analysed, in the context of the resulting PV patchiness, using metrics such as the eddy enstrophy. A passive tracer is included in the model, allowing a visualisation of horizontal transport across the polar vortex. Differences in mixing properties arising from differing extents of patchiness in the vortex may help explain temporal variations in dust deposits across polar regions, which are visible in the polar layered deposits and may help increase knowledge of Mars’ paleoclimate.
How to cite: Hughes, S., Seviour, W., Shipton, J., and Thomson, S.: An idealised model of Martian polar vortex variability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19326, https://doi.org/10.5194/egusphere-egu25-19326, 2025.
Close-in terrestrial planets orbiting M dwarfs can sustain ice cap on the permanent nightside under inefficient heat transport, which can bring potential habitability. However, the amount of ice may be limited considering the water surviving from the steam atmosphere after the runaway greenhouse state, and the condensation process through which water retains is not clear. Here, we use a two-column radiative-convective model to investigate the water condensation process of tidally locked planets after the runaway greenhouse state. We find that this process is determined by two equilibrium states, which results from the competition between the atmospheric greenhouse effect and dayside radiator fin. These equilibrium states are influenced by factors such as stellar flux and uncondensable greenhouse gases. Our result provides an easy method to quantify the amount of water condensed after runaway state and can help to understand water content of M dwarf planets.
How to cite: Ouyang, Y. and Ding, F.: Revival of surface water after the runaway greenhouse on close-in terrestrial planets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3019, https://doi.org/10.5194/egusphere-egu25-3019, 2025.
When life emerged on Earth ~4 Gyr ago, the physical and chemical environments were vastly different from today. For example, the Sun was fainter, small bodies bombarded Earth’s surface, and the atmosphere was reducing. Yet, this seemingly lethal environment turned out to be beneficial for producing the building blocks of life, e.g. amino acids, sugars and nucleobases. The reaction chain to form such complex species can in theory begin with a simple molecule such as hydrogen cyanide (HCN) and take place on the planetary surface, in hypothesised warm little ponds. However, HCN itself is mainly produced in the atmosphere through photochemical reactions. It is therefore important to include the atmospheric production of HCN and its transport to the surface, through rain-out processes, and to understand how these processes are influenced by the physical environment. We use a 1-D photochemical kinetic code, named VULCAN, to study these processes on Early Earth and analogous exoplanets. By varying the physical environment and focusing on HCN chemistry we aim to answer the question: Do we live on a special planet or could (early) Earth be part of a larger population of rocky planets in the universe that has the potential to harbour life? As part of this work, we determine the important chemical pathways for a range of physical environments so they can be used later in 3D climate-chemistry model simulations.
How to cite: Friss, G., Palmer, P. I., and Braam, M.: How unique is our rocky planet as a cradle of life in the universe?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11973, https://doi.org/10.5194/egusphere-egu25-11973, 2025.
M-dwarf stars are smaller and cooler than solar-type stars, yet are the most abundant and long-lived in the Galaxy. They are also more likely to host rocky planets, particularly within the circumstellar Habitable Zone, with the caveat that these planets are likely to be tidally-locked to their host star with one hemisphere permanently illuminated and the other in perpetual darkness. Modelling studies have so far shown that these atmospheres may be protected against collapse on the nightside given sufficient pressure, as well as identifying multiple atmospheric circulation regimes which are determined primarily by planetary rotation rate. Whilst the majority of studies examine simulations from a single model, the use of multimodel intercomparisons (e.g., CUISINES) is becoming increasingly popular, with results suggesting some diversity in simulated atmospheres and climate. Furthermore, with the characterisation of temperate rocky exoplanet atmospheres on the horizon for observers, the resultant ensemble spread may help to constrain uncertainties and degeneracies within future observations. MEGA-MIP aims to build upon the work of predecessors such as THAI and Haqq-Misra et al. (2018), using an ensemble of 3D general circulation models adapted for use in exoplanet climatology to simulate a set of tidally-locked terrestrial planets along the inner edge of the Habitable Zone. Particular emphasis will be placed upon discussing the preliminary results from the intercomparison, which examine the diversity of the global atmospheric circulation, surface climate, and habitability across the distinct circulation regimes introduced by Haqq-Misra et al. (2018).
How to cite: Woodward, H., Rushby, A., and Mayne, N.: MEGA-MIP: M-Earth Global Atmospheres Model Intercomparison Project, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7165, https://doi.org/10.5194/egusphere-egu25-7165, 2025.
On geological timescales, Earth’s atmosphere has evolved from a reducing chemical composition to today’s oxidising composition. Life is thought to have originated in the early reduced environment, with a key role for basic prebiotic compounds such as hydrogen cyanide (HCN) and formaldehyde (H2CO). Rocky exoplanets are found in diverse stellar and planetary environments, inevitably presenting diverse atmospheric compositions. We use VULCAN, a 1D photochemical kinetics code, to test the formation mechanisms of prebiotic compounds like HCN and H2CO on exoplanets orbiting around M-dwarf host stars. We explore the sensitivity of the atmospheric chemistry of these compounds, within broader chemical networks, to prior knowledge of the corresponding chemical reactions and rate coefficients. For each sensitivity experiment, we identify the key pathways that form prebiotic compounds from the background atmospheric species. By inserting these key pathways of one chemical network into another, we attempt to reconcile the inter-network differences. Our work paves the way for implementing the key prebiotic pathways in a 3D climate-chemistry model, which we will briefly outline. Finally, since any observation of an exoplanet will represent only a snapshot of its long-term evolution, we argue that understanding different evolutionary epochs is crucial in the search for biosignatures on rocky exoplanets.
How to cite: Braam, M., Gopaoco, E., Tsai, S.-M., Friss, G., and Palmer, P.: Investigating the chemical pathways to prebiotic compounds in exoplanet atmospheres, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15313, https://doi.org/10.5194/egusphere-egu25-15313, 2025.
Warm rocky exoplanets within the habitable zone of Sun-like stars are favoured targets for current and future missions. Theory indicates these planets could be wet at formation and remain habitable long enough for life to develop. However, it is unclear to what extent an early ocean on such worlds could influence the response of potential biosignatures. In this work we test the climate-chemistry response, maintenance, and detectability of biosignatures in warm, water-rich atmospheres with Earth biomass fluxes within the framework of the planned LIFE mission.
We used the coupled climate-chemistry column model 1D-TERRA to simulate the composition of planetary atmospheres at different distances from the Sun, assuming Earth's planetary parameters and evolution. We increased the incoming instellation by up to 50 percent in steps of 10 percent, corresponding to orbits of 1.00 to 0.82 AU. Simulations were performed with and without modern Earth’s biomass fluxes at the surface. Theoretical emission spectra of all simulations were produced using the GARLIC radiative transfer model. LIFEsim was then used to add noise to and simulate observations of these spectra to assess how biotic and abiotic atmospheres of Earth-like planets can be distinguished.
Increasing instellation leads to surface water vapour pressures rising from 0.01 bar (1.31%, S = 1.0) to 0.61 bar (34.72%, S = 1.5). In the biotic scenarios, the ozone layer survives because hydrogen oxide reactions with nitrogen oxides prevent the net ozone chemical sink from increasing. Methane is strongly reduced for instellations that are 20% higher than that of the Earth due to the increased hydrogen oxide abundances and UV fluxes. Synthetic observations with LIFEsim, assuming a 2.0 m aperture and resolving power of a R = 50, show that ozone signatures at 9.6 micron reliably point to Earth-like biosphere surface fluxes of O2 only for systems within 10 parsecs. The differences in atmospheric temperature structures due to differing H2O profiles also enable observations at 15.0 micron to reliably identify planets with a CH4 surface flux equal to that of Earth's biosphere. Increasing the aperture to 3.5 m increases this range to 22.5 pc.
How to cite: Taysum, B., van Zelst, I., Grenfell, J., Schreier, F., Cabrera, J., and Rauer, H.: Detectability of biosignatures in warm, water-rich atmospheres, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16449, https://doi.org/10.5194/egusphere-egu25-16449, 2025.
The pattern of airy and airless rocky planets presently being uncovered by JWST is a record of what happens when ionospheres are pushed to their limits by their host stars. Orbiting as close to a red dwarf host as the Parker Probe is to the Sun, a massive rocky planet could harbour liquid water oceans beneath an ionosphere several times hotter than its star’s effective temperature, exhibiting spectacular airglow and aurora. Not only is this a distinct and observable possibility, but planets of this kind may make up a significant fraction of habitable worlds.
What maximum temperature can a tightly bound ionosphere, composed primarily of carbon, nitrogen, and oxygen atoms, reach before escaping into space as a hydrodynamic wind? This question lies at the crux of the 500-hour Rocky Worlds DDT Program and the guiding hypothesis of a universal cosmic shoreline.
Locally, the terminal temperatures of these extreme ionospheres are determined by heating from XUV photons emitted by the star’s corona and cooling through collisional excitation of atoms that emit visible and infrared photons. Globally, the thermal structure is determined by photochemistry, fluid dynamics, and electromagnetic interactions. Additionally, stellar cycle variation of ionospheric conditions is likely key to atmospheric evolution. In this talk, we will discuss the key knowns and unknowns in predicting the “edge of airlessness” for the population of rocky exoplanets within the observational reach of the James Webb Space Telescope.
How to cite: Chatterjee, R. D., Blumenthal, S., and Pierrehumbert, R. T.: Exoplanetary Ionospheric Temperatures on the Edge of Airlessness, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19382, https://doi.org/10.5194/egusphere-egu25-19382, 2025.
More than 200 moons exist in our solar system, but no exomoon has been confirmed to date. What kind of exoplanetary systems are possible to host exomoons, and what are the possible ways to detect the exomoons? We conduct N-body orbital simulations for three representative cases that are close to their host stars, and find that the possibility of exomoon existence varies across different systems. TRAPPIST-1 e and GJ 1214 b are possible to host exomoons, although the exomoon orbital stability zones are narrow and close to the planets. WASP-121 b is unlikely to host exomoons because the planetary radius is nearly half of the Hill radius, and beyond the Hill sphere, the the star's gravitational influence dominates the exomoon. Close-in airless exomoons maintain large temperature difference between the day and night hemispheres. The large day-night temperature contrast of the exomoon significantly amplifies the total thermal phase curve amplitude of an exomoon-exoplanet system, especially for large, airless exomoons orbiting exoplanets with atmospheres. When the hypothetical exomoon transits or is blocked by the exoplanet, the transit depth varies with the planetary phase, and the occultation depth varies with the exomoon's phase. For an Earth-sized exomoon orbiting GJ 1214 b, the occultation signal can reach 100 ppm. Without extracting the exomoon signal, retrieving the planetary temperature distribution from observed thermal phase curve is likely to overestimate the planetary day-night temperature contrast, and underestimate the planetary horizontal heat transport. With longer observation time and greater time resolution from infrared space telescopes in the future, detecting exomoons through thermal phase curves is possible.
How to cite: Song, X., Yang, J., and Ouyang, Y.: Is It Possible to Detect Airless Exomoons Through Thermal Phase Curves?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6151, https://doi.org/10.5194/egusphere-egu25-6151, 2025.
HDO is an isotopic form of water that can provide clues about the history and evolution of water on terrestrial planets. By comparing the D/H ratio derived from the abundance ratio of HDO and H2O on Venus with that of other planets or comets that have similar origins, we can estimate how much water Venus stored and lost during its formation and evolution. The Venus Plobal Climate Model (VPCM) developed by several laboratories (LMD, LATMOS) of Institute Pierre-Simon Laplace (IPSL, in Paris area) can simulate the chemical and dynamical processes of the Venusian atmosphere. However, HDO has so far not been included in the VPCM before. In this work, we first implement HDO in the gas and liquid phases as two additional tracers of the model to investigate their spatial and temporal distributions. As an isotope of water, HDO participates to all the chemical and physical processes in which water is involved. Furthermore, we have analyzed the influence of fractionation of HDO during condensation, and photolysis processes on the resulting D/H.
How to cite: Li, D., Montmessin, F., Lefèvre, F., Streel, N., Lebonnois, S., and Petzold, G.: Investigating the effects of fractionation on HDO cycle and D/H on Venus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10793, https://doi.org/10.5194/egusphere-egu25-10793, 2025.
A regional dust storm was observed in the northern spring of Martian Year 35, a period characterized by a relatively cold and clear atmosphere. Satellite observations and general circulation model simulations indicate that the atmospheric temperature response to this early regional dust storm closely resembles an equatorial counterpart of the regional dust storm responses typically observed during the high dust loading season. Atmospheric heating in the dust-lifting region was primarily driven by shortwave radiative heating of dust particles. Anomalous cooling in the northern mesosphere and heating responses in the southern troposphere were associated with dust-modulated gravity waves and planetary waves, respectively. Inhomogeneous heating from dust distribution during the storm generated anomalous atmospheric waves, significantly enhancing southward meridional circulation and lifting water vapor in the lower tropical troposphere. This dust storm substantially increased meridional water transport from the Northern to the Southern Hemisphere, with pronounced longitudinal asymmetry underscoring the influence of tropical topographic features on water vapor transport.
How to cite: Sun, C., Yang, C., Li, T., Lai, D., and Fang, X.: The Atmospheric Response to an Unusual Early-Year Martian Dust St, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4732, https://doi.org/10.5194/egusphere-egu25-4732, 2025.
The deuterium/hydrogen isotopic ratio, D/H, is one of the keys to understand the origin of water on terrestrial bodies within the Solar System and its evolution over time in their atmospheres.
In the atmosphere of Mars, this D/H ratio is on average 5 to 6 times higher than what is found on Earth (Earth oceans serve as a reference with the Vienna Standard Mean Ocean Water, VSMOW). Although Martian water is present only in very low quantities (100 ppmv on average), its high deuterium enrichment points to a wetter past for the red planet, which is supported by various geological indicators (valleys, ancient lakes, shorelines). To understand this result and how the water has escaped from Mars' atmosphere, the study of HDO – the main source of changes in the D/H ratio on the planet – and its annual cycle appears essential, particularly regarding its seasonal behavior in the upper atmosphere where water vapor can be photodissociated and then ejected.
The Mars PCM (Planetary Climate Model) simulates the Martian atmosphere physical, chemical and dynamical processes; including water ice cloud-related phenomena, such as condensation, which play a significant role in the relative behavior of HDO. This model, coupled with observations and data from ACS (Atmospheric Chemistry Suite), has shed light on the HDO cycle in recent years. However, differences still exist between the model results and the observations. This is particularly the case for the vertical distribution of water vapor in the upper atmosphere. Some improvements to the MPCM, e.g. dust, water clouds and gravity waves are provided, and their effects are studied and discussed. One of them is the implementation of a more realistic dust particles size distribution in the model. These improvements provide a more realistic HDO cycle as well as a more reliable source of comparison with the ACS observations. The goal is to further understand the nature and origin of the high deuterium enrichment on the red planet.
How to cite: Petzold, G., Montmessin, F., Naar, J., and Millour, E.: Recent updates on HDO cycle modeling on Mars, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10787, https://doi.org/10.5194/egusphere-egu25-10787, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 3
EGU25-5310 | Posters virtual | VPS27
Observed Martian High-frequency gravity waves by Zhurong and Perseverance rovers before / after a regional dust stormThu, 01 May, 14:00–15:45 (CEST) | vP3.1
This study investigated high-frequency gravity waves (HFGWs) observed by the Zhurong/Tianwen-1 and Perseverance/Mars 2020 rovers between 09:00 and 11:00 local time, from Ls 140° to 165° in Mars Year 36. By analyzing the eccentricity of hodographs for monochromatic wind perturbations obtained from the horizontal wind perturbation, HFGWs were identified via their predominantly linear characteristics.The propagation directions of these waves were determined using polarization relationships from the linear theory of HFGWs. The stability of the background atmosphere was estimated from the Dynamic Meteorology Laboratory general circulation model simulation. The frequency of HFGWs doubled following the onset of a regional dust storm (RDS) in the Utopia Planitia region, where the Zhurong rover landed. The HFGWs observed by Zhurong predominantly propagated in a north-south direction before the RDS and then in an east-west direction afterward. The changes in propagation direction were likely related to atmospheric instability and the background wind changes before and after the storm.
How to cite: Yang, C., Sun, C., Ban, C., Lai, D., Wu, Z., Fang, X., and Li, T.: Observed Martian High-frequency gravity waves by Zhurong and Perseverance rovers before / after a regional dust storm, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5310, https://doi.org/10.5194/egusphere-egu25-5310, 2025.
