Future observatories may enable the study of atmospheres of terrestrial planets from the habitable zones around various types of stars. Regardless of what will be found, this will provide major insights into planetary science, as well as doubtlessly result in profound paradigm shifts. In anticipation of these telescopes, much effort is going into simulating potential planets, atmospheres, and specific spectral signatures that may be expected to be observed. These include surface and atmospheric biosignatures, typically leveraging our Earth as a template for biology. In this talk, our teams’ efforts in simulating habitable planets around K and G stars will be presented.

Climate simulations
Climate simulation using both ROCKE-3D (Adams, PI Turnbull) and ExoCam (Wolf, PI: Lobo) are presented, with Earth-like planets but considering different types of host stars, rotation rates, obliquities, and thus widely varying climate states.

Spectral simulations
The Planetary Spectrum Generator is used to simulate 3D spectra from the planets (Villanueva et al., 2018). Following the recent developments described in Kofman et al., 2024, spectra, and RGB representations are simulated at different times of year and the detectability of different biomarkers is considered.

Critical in our spectral evaluations of the climate models are updated cloud parameterization strategies. Often, spectroscopic representations of GCMs employ simplified representation of clouds, or assume the planet is cloud-free. Particular effort is dedicated here to ensure accurate representation of clouds in the atmospheres, as this strongly affects the detectability of the spectroscopic features of interest.

The figure below provides an example from Kofman et al., 2024 of a simulation of Earth as an exoplanet, where the planet is observed in reflected light as might be seen with a future Habitable Worlds Observatory.

How to cite: Kofman, V., Turnbull, M., Lobo, A., Kopparapu, R., Fauchez, T., Villanueva, G., Wolf, E., Haqq-Misra, J., and Merrelli, A.: Spectral signatures from the Habitable Zone, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1316, https://doi.org/10.5194/epsc-dps2025-1316, 2025.

Introduction:  The hunt for biosignatures in the atmospheres of exoplanets is a central goal of many cutting-edge instruments currently in operation [1], under construction [2] or otherwise proposed [3]. The starting point of this search are the planets that can in theory support liquid water on their surfaces,  i.e. inside the Circumstellar Habitable Zone (CHZ, [4]). Around two thirds of the 72 known rocky exoplanets in the CHZ orbit M-type dwarfs [5]. The HZ of this class of stars is well within the region of the system where the gravitational interaction of the central body force the planet into a 1:1 spin-orbit ratio [6]. The climate of these planets cannot be studied using standard 1-D Energy Balance Models (EBM, [7]) and most investigators rely on computationally expensive 3-D General Circulation Models (GCM, e.g. [8]). This severely limits the number of  combinations of unconstrained or poorly constrained planetary parameters that can be tested to determine how much robust the habitability of these planets actually is.

Model: Here, we present a new 1-D EBM specifically tailored for the study of tidally locked rocky temperate exoplanets. This model discretizes the surface of the planet in a number of zones defined with respect to the substellar point. The surface temperature profile as a function of the angular distance with the terminator is determined by the equilibrium between the absorbed stellar radiation, the outgoing longwave radiation and the horizontally transferred heat, treated as diffusive. By defining an interval of temperatures suitable for the survival of life (here, 0-100°C, [9]), it is possible to derive the fraction of the planetary surface that is habitable. This model is coupled with a state-of-the-art radiative transfer model (EOS, [10]), and takes into account the contribution of clouds, the surface albedo and the atmospheric CO2 condensation on the nightside on the surface temperature [11,12]. Finally, the emission temperature of the planet at different points of the surface can be used to produce synthetic infrared phase curves. The free parameters of the model have been calibrated against both 3-D GCMs [13] and a priori theoretical calculations [14]. While the use of 1-D EBM on tidally locked planets is not entirely new (see e.g. [15,16,17]), previous models were simpler and generally focused on a specific climatological aspect.

Results: We have applied our new EBM for tidally locked planets to the eight temperate Earths and Super-Earths of the ESA Ariel Mission Target List (TRAPPIST-1c, -1d, -1e, -1f and -1g, LHS 1140b, K2-18b and TOI-1468c), all of which orbit M-type stars. In particular, we mapped the fractional habitability as a function of the surface pressure (Ps) in the [0.1, 10] bar range, and the CO2 mixing ratio (xCO2) in the [-4, 0] dex range for a N2-CO2-H2O atmosphere. Both line and collisional induced absorptions of the involved gases were taken from the HITRAN2020 repository [18]. All the targets were modeled as aquaplanets. Our preliminary analysis showed that: (i) TRAPPIST-1c and TOI-1468c enter a runaway greenhouse state under all the tested combinations; (ii) TRAPPIST-1f, -1g and LHS 1140 b are habitable only in presence of dense (> 10 bar) and CO2-rich (> 1-10 %) atmospheres, but for LHS 1140 b this is incompatible with the observationally derived upper limit on the xCO2 (see Fig.1); (iii) TRAPPIST-1d is habitable only for CO2-poor atmospheres, which might limit the action of Earth-like photosynthetic organisms and thus the production of detectable biosignatures [19]; (iv) TRAPPIST-1e and K2-18b are the best targets for astrobiological studies in the sample. However, in both cases there exist a limiting pressure above which these planets likely enter a runaway greenhouse state. For K2-18b this limiting pressure is ~3 bars for a xCO2≥1% , which clashes with interior structure models of the planet predicting a deep (albeit H2-dominated) atmosphere [20].

Figure 1: The fraction of the surface within the 0-100 °C interval as a function of Ps and xCO2, for the planet LHS 1140 b. The  white dashed line represents the upper limit on the CO2 mixing ratio as derived by observations [21]. The hatched region identifies the cases in which the atmosphere is unstable against collapse, caused by the condensation of CO2 on the planetary nightside. The snowflake symbol identifies the region of no habitability as caused by the onset of a planetary Snowball state.

Future prospects: We plan to expand the atmospheric pressure range and to test different atmospheric compositions, including H2-dominated cases (for K2-18b) and atmospheres with a varying amount of CH4. Our habitability maps can be readily compared with observational data, as done in Fig. 1, to rapidly assess the astrobiological relevance of any target for very large sets of planetary parameter combinations.

References: [1] Greene T. et al. (2016), ApJ, 817, 17. [2] Tinetti G. et al. (2018),  ExA, 46, 135. [3] Quanz S. (2022), A&A, 664, 21.  [4] Kopparapu R.-K. (2013), ApJ, 765, 131. [5] Habitable Worlds Catalog, https://phl.upr.edu/hwc. [6] Kasting J. et al. (1993), Icar, 101, 108. [7] North G. et al. (1981), RvGSP, 19, 91. [8] Lobo A. & Shields A. (2024), ApJ, 972, 71. [9] Vladilo G. et al. (2015), ApJ, 804, 50. [10] Simonetti P. et al. (2022), ApJ, 925, 105. [11] Biasiotti L. et al. (2022), MNRAS, 514, 5105. [12] Shields A. et al. (2013), AsBio, 13, 8. [13] Sergeev D. et al. (2022), PSJ, 3, 212. [14] Koll D. (2022), ApJ, 924, 134. [15] Kite E. et al. (2011), ApJ, 743, 41. [16] Checlair J. et al. (2017), ApJ, 835, 132. [17] Haqq-Misra J.& Hayworth B. (2022), PSJ, 3, 32. [18] Gordon I. et al. (2022), JQSRT, 27707949. [19] Gerhart L. & Ward J. (2010), NPhyt, 188, 3. [20] Madhusudhan N. et al. (2020), 891, 7. [21] Cadieux C. et al. (2024), ApJ, 970, 2.

How to cite: Simonetti, P., Ivanovski, S., Biasiotti, L., Vladilo, G., Monai, S., Dogo, F., Calderone, L., Politi, R., and Turrini, D.: A new energy balance model to map the habitability of tidally locked rocky planets: application to the Ariel target list, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1010, https://doi.org/10.5194/epsc-dps2025-1010, 2025.

How to cite: Glover, J. and Cowan, N.: The search for reflected light from 51 Peg b at high spectral resolution, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-369, https://doi.org/10.5194/epsc-dps2025-369, 2025.

Understanding the role of a planet’s interior in establishing habitable conditions is a critical, yet often overlooked, aspect of planetary evolution. The atmosphere and interior of a rocky planet do not form separate systems, but are coupled by a complex network of feedback processes which link the evolution of the atmosphere to the evolution of the interior. For example, volcanic outgassing of volatile species from the planet’s silicate mantle shapes the atmospheric composition, temperature, and pressure, but the exact composition of outgassed species not only depends on the volatile content and oxidation state of the mantle, but also on the current state - i.e., pressure, composition, and temperature - of the atmosphere. As such, the composition of the earliest atmosphere can drastically change the evolutionary path of the planet. In addition, the early surface conditions set the stage for which stabilizing feedback cycles initiate. For example, the carbonate-silicate cycle on Earth, which regulates the amount of CO2 in the atmosphere to ensure a temperate climate, heavily relies on liquid water for surface weathering, and on plate tectonics to transport carbonates back into the mantle.

However, many terrestrial exoplanets are expected to be stagnant-lid planets, i.e. those without active plate tectonics, such as Mars. Although the interior-atmosphere coupling in these planets is weaker, feedback cycles still play an important role in their evolution, and some form of carbonate-silicate cycling may still work even in the absence of plate tectonics. Stagnant-lid planets therefore offer an ideal test bed to explore the baseline conditions required for habitability.

In an earlier work, we showed that long-term habitability on stagnant-lid planets depends on a narrow range of mantle volatile contents and redox states. In this study, we explore in particular how the primary atmosphere, outgassed during the magma ocean stage of formation, predisposes a stagnant-lid planet to different long-term atmospheric states. For this, we use our 1D planet evolution code TEMPURA to simulate the long term coupled evolution of planet interior and atmosphere, including a comprehensive array of feedback processes between atmosphere and interior, such as a CO2 weathering cycle, volcanic outgassing, a water cycle between ocean and atmosphere, greenhouse heating, as well as atmospheric escape processes.

We aim to identify the critical processes and conditions that produce long-term habitable conditions (even in the absence of active tectonic recycling) across a wide range of terrestrial planets.

How to cite: Baumeister, P., Noack, L., and Brachmann, C.: The influence of primordial atmospheric composition on the long-term habitability of stagnant-lid planets, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-586, https://doi.org/10.5194/epsc-dps2025-586, 2025.

Earth is the only known habitable or inhabited planet to date. However, since we are not yet able to observe the atmospheres of Earth-like planets orbiting Sun-like stars, the search for life outside our Solar system has focused on M-Earths, which are rocky planets orbiting in the habitable zones of M-dwarfs. Although JWST can, in theory, observe their atmospheres, these observations are time-consuming and difficult to interpret. M-Earth climates are also expected to differ significantly from Earth’s. Therefore, in order to make good use of telescope time, it is necessary to understand an M-Earth’s possible climate states and how these might present in observations. 

M-dwarf systems are compact, so M-Earths are expected to be tidally locked to their stars. A synchronously rotating planet must circulate heat from the substellar point to its permanent nightside in order to maintain its atmosphere. The instellation gradient gives rise to the “eyeball” climate state: a frozen nightside and a temperate region around the substellar point where liquid water can exist. An M-Earth’s habitability, in the traditional sense, depends on whether or not water is present in this region. However, the surfaces of M-Earths are not accessible to observations, so it is relevant to ask whether this information can be recovered in transit spectra.

In this work, we use the 3D climate model ExoPlaSim to simulate a vast parameter space of M-Earth climates and synthetic observations. We systematically vary dayside land cover and the mass of the atmosphere, since these variables have important climate implications, but will not be known a priori for a given planet. We find that both the amount and the location of land on the dayside determine the abundance of water vapour, which together with the atmosphere mass determines how much energy is transported to the nightside. A large range of possible climates arise from variations in these parameters. 

To determine the observational uncertainties associated with these climate differences, we generate synthetic water vapour transmission spectra from our climate simulations using petitRADTRANS. We find that the differences in water vapour abundance between simulations are recovered in the spectra, but that JWST is unlikely to be able to distinguish between different climate states from this information because the signal is too small, especially when clouds are included in the radiative transfer calculation. There is also overlap between the effects of land fraction, land configuration, and atmosphere mass on the size of the water vapour spectral feature, such that a planet’s climate state cannot be unambiguously identified from this information alone. Consequently, observers will need to account for these climate uncertainties when interpreting M-Earth spectra.

How to cite: Macdonald, E., Menou, K., Lee, C., and Paradise, A.: Fundamental uncertainties in M-Earth transit spectra due to unconstrained climate states, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1692, https://doi.org/10.5194/epsc-dps2025-1692, 2025.

 Habitable terrestrial exoplanets around M dwarfs are remarkable targets due to the ease to detect and characterize. These planets are thought to have a different climate from solar system planets because these planets are expected to be in a tidally-locked state due to closer orbits and strong tidal forces. According to the studies of planet formation, terrestrial exoplanets around M dwarfs could sustain a large amount of surface water (tens or hundreds of Earth ocean mass). Such planets with large amount water (deep ocean) would be globally ocean covered, resulting in no continents.

 Earth’s ocean circulation largely affects the climate (e.g. meridional heat transport, water cycle). Ocean circulation is roughly classified into wind-driven circulation and density-driven circulation. In particular, density-driven circulation, which passes deep ocean, is affected by sea water temperature and salinity, resulting from heat exchange to atmosphere and salinity change by precipitation or sea ice formation. Although salinity has large influences on ocean behavior such as strength of ocean circulation and condition of sea ice formation, this effect on tidally-locked ocean planet has been still unknown.

 To investigate the influence on climate by salinity, first, we developed an atmospheric and oceanic global climate model (AOGCM) for exoplanets based on MIROC4m. Both atmospheric part and oceanic part solve 3-dimensional hydrodynamics, thermodynamics, and tracer transports (such as water vapor in the atmosphere and salinity in the ocean), and a coupler exchanges the information about the sea surface between both parts for example radiative heating and evaporation. By using the AOGCM, we simulated the TRAPPIST-1e’s climate assuming  an ocean covered planet. We set 1 Earth ocean mass (3200 m depth because of its planetary radius) with Earth-like salinity (35.4 psu) or pure water (0 psu). In addition to the AOGCM simulations, we also run AGCM simulation which includes slab ocean instead of ocean GCM part.  We integrated over 2000 years for AOGCM simulations and 50 years for AGCM simulation.

 An eyeball-shape open sea appears on the dayside according to the AGCM simulation, however, AOGCM simulations result in slushball-shape open sea due to the equatorial ocean currents. Comparing the results of AOGCM results, we found that salinity expands open sea distribution due to freezing-point depression and affects intensity of surface ocean current and vertical circulation. In this presentation, we will show the physical mechanisms of these differences by salinity.

How to cite: Taniguchi, K., Kodama, T., Higuchi, T., Obase, T., and Genda, H.: Effects of salinity on tidally-locked aqua planets’ climate with a coupled atmosphere and ocean GCM, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-246, https://doi.org/10.5194/epsc-dps2025-246, 2025.