Mineral dust increases the habitability of terrestrial planets but confounds biomarker detection

Identification of habitable planets beyond our solar system is a key goal of current and future space missions. Yet habitability depends not only on the stellar irradiance, but equally on constituent parts of the planetary atmosphere. Here we show, for the first time, that radiatively active mineral dust will have a significant impact on the habitability of Earth-like exoplanets. On tidally-locked planets, dust cools the day-side and warms the night-side, significantly widening the habitable zone. Independent of orbital configuration, we suggest that airborne dust can postpone planetary water loss at the inner edge of the habitable zone, through a feedback involving decreasing ocean coverage and increased dust loading. The inclusion of dust significantly obscures key biomarker gases (e.g. ozone, methane) in simulated transmission spectra, implying an important influence on the interpretation of observations.We demonstrate that future observational and theoretical studies of terrestrial exoplanets must consider the effect of dust

TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI): Motivations and protocol version 1.0

This is the final version. Available from European Geosciences Union via the DOI in this record. ExoCAM (Wolf and Toon, 2015) is available on GitHub: https://github.com/storyofthewolf/ExoCAM (last access: 8 February 2020). The Met Office Unified Model is available for use under license; see http://www.metoffice.gov.uk/research/modelling-systems/unified-model (Met Office, 2020, last access: 8 February 2020). ROCKE-3D is public domain software and available for download for free from https://simplex.giss.nasa.gov/gcm/ROCKE-3D/ (last access: 8 February 2020, NASA Goddard Institute for Space Studies, 2020a). Annual tutorials for new users take place annually, whose recordings are freely available online at https://www.youtube.com/user/NASAGISStv/playlists?view=50&sort=dd&shelf_id=15 (last access: 8 February 2020b, NASA Goddard Institute for Space Studies, 2020b). LMDG is obtainable upon request from Martin Turbet ([email protected]) and François Forget ([email protected]).Upcoming telescopes such as the James Webb Space Telescope (JWST), the European Extremely Large Telescope (E-ELT), the Thirty Meter Telescope (TMT) or the Giant Magellan Telescope (GMT) may soon be able to characterize, through transmission, emission or reflection spectroscopy, the atmospheres of rocky exoplanets orbiting nearby M dwarfs. One of the most promising candidates is the late M-dwarf system TRAPPIST-1, which has seven known transiting planets for which transit timing variation (TTV) measurements suggest that they are terrestrial in nature, with a possible enrichment in volatiles. Among these seven planets, TRAPPIST-1e seems to be the most promising candidate to have habitable surface conditions, receiving ~ 66 % of the Earth's incident radiation and thus needing only modest greenhouse gas inventories to raise surface temperatures to allow surface liquid water to exist. TRAPPIST-1e is, therefore, one of the prime targets for the JWST atmospheric characterization. In this context, the modeling of its potential atmosphere is an essential step prior to observation. Global climate models (GCMs) offer the most detailed way to simulate planetary atmospheres. However, intrinsic differences exist between GCMs which can lead to different climate prediction and thus observability of gas and/or cloud features in transmission and thermal emission spectra. Such differences should preferably be known prior to observations. In this paper we present a protocol to intercompare planetary GCMs. Four testing cases are considered for TRAPPIST-1e, but the methodology is applicable to other rocky exoplanets in the habitable zone. The four test cases included two land planets composed of modern-Earth and pure-CO2 atmospheres and two aqua planets with the same atmospheric compositions. Currently, there are four participating models (LMDG, ROCKE-3D, ExoCAM, UM); however, this protocol is intended to let other teams participate as well.NASA Planetary Science Division's Internal Scientist Funding ModelEuropean Union’s Horizon 2020NASA Astrobiology Progra

TRAPPIST Habitable Atmosphere Intercomparison (THAI) workshop report

This is the final version. Available on open access from IOP Publishing via the DOI in this recordThe era of atmospheric characterization of terrestrial exoplanets is just around the corner. Modeling prior to observations is crucial in order to predict the observational challenges and to prepare for the data interpretation. This paper presents the report of the TRAPPIST Habitable Atmosphere Intercomparison (THAI) workshop (14-16 September 2020). A review of the climate models and parameterizations of the atmospheric processes on terrestrial exoplanets, model advancements and limitations, as well as direction for future model development was discussed. We hope that this report will be used as a roadmap for future numerical simulations of exoplanet atmospheres and maintaining strong connections to the astronomical community

The TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI). Part II: Moist Cases -- The Two Waterworlds

This is the author accepted manuscript.Data accesssibility: All our GCM THAI data are permanently available for download here: https://ckan.emac.gsfc.nasa.gov/organization/thai, with variables described for each dataset. If you use those data please cite the current paper and add the following statement: “THAI data have been obtained from https://ckan.emac.gsfc.nasa. gov/organization/thai, a data repository of the Sellers Exoplanet Environments Collaboration (SEEC), which is funded in part by the NASA Planetary Science Divisions Internal Scientist Funding Model.”To identify promising exoplanets for atmospheric characterization and to make the best use of observational data, a thorough understanding of their atmospheres is needed. 3D general circulation models (GCMs) are one of the most comprehensive tools available for this task and will be used to interpret observations of temperate rocky exoplanets. Due to various parameterization choices made in GCMs, they can produce different results, even for the same planet. Employing four widely-used exoplanetary GCMs -- ExoCAM, LMD-Generic, ROCKE-3D and the UM -- we continue the TRAPPIST-1 Habitable Atmosphere Intercomparison by modeling aquaplanet climates of TRAPPIST-1e with a moist atmosphere dominated by either nitrogen or carbon dioxide. Although the GCMs disagree on the details of the simulated regimes, they all predict a temperate climate with neither of the two cases pushed out of the habitable state. Nevertheless, the inter-model spread in the global mean surface temperature is non-negligible: 14 K and 24 K in the nitrogen and carbon dioxide dominated case, respectively. We find substantial inter-model differences in moist variables, with the smallest amount of clouds in LMD-Generic and the largest in ROCKE-3D. ExoCAM predicts the warmest climate for both cases and thus has the highest water vapor content, the largest amount and variability of cloud condensate. The UM tends to produce colder conditions, especially in the nitrogen-dominated case due to a strong negative cloud radiative effect on the day side of TRAPPIST-1e. Our study highlights various biases of GCMs and emphasizes the importance of not relying solely on one model to understand exoplanet climates.Science and Technology Facilities CouncilUKRILeverhulme TrustEuropean Union Horizon 2020Gruber Foundatio

The CUISINES Framework for Conducting Exoplanet Model Intercomparison Projects, Version 1.0

This is the author accepted manuscript.As JWST begins to return observations, it is more important than ever that exoplanet climate models can consistently and correctly predict the observability of exoplanets, retrieval of their data, and interpretation of planetary environments from that data. Model intercomparisons play a crucial role in this context, especially now when few data are available to validate model predictions. The CUISINES Working Group of NASA’s Nexus for Exoplanet Systems Science (NExSS) supports a systematized approach to evaluating the performance of exoplanet models, and provides here a framework for con 24 ducting community-organized exoplanet Model Intercomparison Projects (exoMIPs). The CUISINES framework adapts Earth climate community practices specifically for the needs of the exoplanet re 26 searchers, encompassing a range of model types, planetary targets, and parameter space studies. It is intended to help researchers to work collectively, equitably, and openly toward common goals. The CUISINES framework rests on five principles: 1) Define in advance what research question(s) the exoMIP is intended to address. 2) Create an experimental design that maximizes community participation, and advertise it widely. 3) Plan a project timeline that allows all exoMIP members to participate fully. 4) Generate data products from model output for direct comparison to observations. 5) Create a data management plan that is workable in the present and scalable for the future. Within the first years of its existence, CUISINES is already providing logistical support to 10 exoMIPs, and will continue to host annual workshops for further community feedback and presentation of new exoMIP ideas.GSFC Sellers Exoplanet Environments Collaboration (SEEC)NASANatural Sciences and Engineering Research Council of Canada (NSERC)Canadian Space AgencyEuropean Research Council (ERC)Max Planck SocietyUKRIScience and Technology Facilities Council (STFC)Leverhulme TrustSNS

The TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI). Part III: Simulated Observables – The return of the spectrum

This is the author accepted manuscriptThe TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI) is a community project that aims to quantify how differences in general circulation models (GCMs) could impact the climate prediction for TRAPPIST-1e and, subsequently its atmospheric characterization in transit. Four GCMs have participated in THAI so far: ExoCAM, LMD-Generic, ROCKE-3D and the UM. This paper, focused on the simulated observations, is the third part of a trilogy, following the analysis of two land planet scenarios (Part I) and two aquaplanet scenarios (Part II). Here, we show a robust agreement between the simulated spectra and the number of transits estimated to detect the land planet atmospheres. For the cloudy aquaplanet ones,a 5–σ detection of CO2 could be achieved in about 10 transits if the atmosphere contains at least 1 bar of CO2. That number can vary by 41–56% depending on the GCM used to predict the terminator profiles, principally due to differences in the cloud deck altitude, with ExoCAM and LMD-G producing higher clouds than ROCKE-3D and UM. Therefore, for the first time, this work provides “GCM uncertainty error bars” of ∼ 50% that need to be considered in future analyses of transmission spectra. We also analyzed the inter-transit variability induced by weather patterns and changes of terminator cloudiness between transits. Its magnitude differs significantly between the GCMs but its impact on the transmission spectra is within the measurement uncertainties. THAI has demonstrated the importance of model intercomparison for exoplanets and also paved the way for a larger project to develop an intercomparison meta-framework, namely the Climates Using Interactive Suites of Intercomparisons Nested for Exoplanet Studies (CUISINES).Science and Technology Facilities Council (STF)UKRILeverhulme TrustEuropean Union Horizon 2020Gruber FoundationSwiss National Science FoundationNAS

The TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI). Part I: Dry Cases – The fellowship of the GCMs

This is the author accepted manuscript.Data accessibility: All our GCM THAI data are permanently available for download here: https://ckan.emac.gsfc.nasa.gov/organization/thai, with variables described for each dataset. If you use these data please cite the current paper and add the following statement: "THAI data have been obtained from https://ckan.emac.gsfc.nasa.gov/organization/thai, a data repository of the Sellers Exoplanet Environments Collaboration (SEEC), which is funded in part by the NASA Planetary Science Divisions Internal Scientist Funding Model." Scripts to process the THAI data are available on GitHub: https://github.com/projectcuisinesWith the commissioning of powerful, new-generation telescopes such as the JWST and the ground-based ELTs, the first characterization of a high-molecular-weight atmosphere around a temperate rocky exoplanet is imminent. Atmospheric simulations and synthetic observables of target exoplanets are essential to prepare and interpret these observations. Here we report the results of the first part of the THAI (TRAPPIST-1 Habitable Atmosphere Intercomparison) project, which compares 3D numerical simulations performed with four state-of-the-art Global Climate Models (ExoCAM, LMD-Generic, ROCKE-3D, Unified Model) for the potentially habitable target TRAPPIST-1e. In this first part, we present the results of dry atmospheric simulations. These simulations serve as a benchmark to test how radiative transfer, subgrid-scale mixing (dry turbulence and convection) and large-scale dynamics impact the climate of TRAPPIST-1e and consequently the transit spectroscopy signature as seen by JWST. To first order, the four models give results in good agreement. The inter-model spread in the global mean surface temperature amounts to 7K (6K) for the N2-dominated (CO2-dominated, respectively) atmosphere. The radiative fluxes are also remarkably similar (inter-model variations less than 5%), from the surface (1bar) up to atmospheric pressures ∼5millibar. Moderate differences between the models appear in the atmospheric circulation pattern (winds) and the (stratospheric) thermal structure. These differences arise between the models from (1) large scale dynamics because TRAPPIST-1e lies at the tipping point between two different circulation regimes (fast and Rhines rotators) in which the models can be alternatively trapped; and (2) parameterizations used in the upper atmosphere such as numerical damping.UK Research and InnovationScience and Technology Facilities CouncilEuropean Union Horizon 2020Leverhulme TrustNAS

CAMEMBERT: A mini-Neptunes GCM intercomparison, protocol version 1.0. A CUISINES model intercomparison project.

This is the author accepted manuscript.The data resulting from the simulations and analysis will be uploaded to the CAMEMBERT permanent repository at https://ckan.emac.gsfc.nasa.gov/organization/cuisines-camembert by participating scientists. These data will be made available for public access upon the publication of the results. Pre-publication access can be requested by contacting the authors. Inputs described in this protocol and scripts related to the analysis of data and production of plots for the publications will be made available on the CAMEMBERT GitHub repository at https://github.com/projectcuisines/camembert. Inputs will be available immediately while scripts to reproduce results will be made publicly available upon the publication of the results.With an increased focus on the observing and modelling of mini-Neptunes, there comes a need to better understand the tools we use to model their atmospheres. In this paper, we present the protocol for the CAMEMBERT (Comparing Atmospheric Models of Extrasolar Mini-neptunes Building and Envisioning Retrievals and Transits) project, an intercomparison of general circulation models (GCMs) used by the exoplanetary science community to simulate the atmospheres of mini-Neptunes. We focus on two targets well studied both observationally and theoretically with planned JWST Cycle 1 observations: the warm GJ 1214b and the cooler K2-18b. For each target, we consider a temperature-forced case, a clear sky dual-grey radiative transfer case, and a clear sky multi band radiative transfer case, covering a range of complexities and configurations where we know differences exist between GCMs in the literature. This paper presents all the details necessary to participate in the intercomparison, with the intention of presenting the results in future papers. Currently, there are eight GCMs participating (ExoCAM, Exo-FMS, FMS PCM, Generic PCM, MITgcm, RM-GCM, THOR, and the UM), and membership in the project remains open. Those interested in participating are invited to contact the authors.Science and Technology Facilities Council (STF)UK Research and InnovationLeverhulme TrustInstitute of PhysicsSNSF Ambizione FellowshipGSFC Sellers Exoplanet Environments Collaboration (SEEC)European Research Council (ERC