Transformational astrophysics and exoplanet science with Habitable Worlds Observatory's High Resolution Imager
White paper submitted to the UK Space Agency's initiative "UK Space Frontiers 2035
Abstract:
Habitable Worlds Observatory (HWO) will be NASA’s flagship space telescope of the 2040s, designed to search for life on other planets and to transform broad areas of astrophysics. NASA are
seeking international partners, and the UK is well-placed to lead the design and construction of its
imaging camera — which is likely to produce the mission’s most visible public impact. Early participation in the mission would return investment to UK industry, and bring generational leadership for
the UK in space science, space technology, and astrophysics.
seeking international partners, and the UK is well-placed to lead the design and construction of its
imaging camera — which is likely to produce the mission’s most visible public impact. Early participation in the mission would return investment to UK industry, and bring generational leadership for
the UK in space science, space technology, and astrophysics.
Simulating biosignatures from pre-oxygen photosynthesizing life on TRAPPIST-1e
Monthly Notices of the Royal Astronomical Society, Volume 531, Issue 1, pp.468-494 (2024)
Abstract:
In order to assess observational evidence for potential atmospheric biosignatures on exoplanets, it will be essential to test whether spectral fingerprints from multiple gases can be explained by abiotic or biotic-only processes. Here, we develop and apply a coupled 1D atmosphere-ocean-ecosystem model to understand how primitive biospheres, which exploit abiotic sources of H2, CO, and O2, could influence the atmospheric composition of rocky terrestrial exoplanets. We apply this to the Earth at 3.8 Ga and to TRAPPIST-1e. We focus on metabolisms that evolved before the evolution of oxygenic photosynthesis, which consume H2 and CO and produce potentially detectable levels of CH4. O2-consuming metabolisms are also considered for TRAPPIST-1e, as abiotic O2 production is predicted on M-dwarf orbiting planets. We show that these biospheres can lead to high levels of surface O2 (approximately 1–5 per cent) as a result of CO consumption, which could allow high O2 scenarios, by removing the main loss mechanisms of atomic oxygen. Increasing stratospheric temperatures, which increases atmospheric OH can reduce the likelihood of such a state forming. O2-consuming metabolisms could also lower O2 levels to around 10 ppm and support a productive biosphere at low reductant inputs. Using predicted transmission spectral features from CH4, CO, O2/O3, and CO2 across the hypothesis space for tectonic reductant input, we show that biotically produced CH4 may only be detectable at high reductant inputs. CO is also likely to be a dominant feature in transmission spectra for planets orbiting M-dwarfs, which could reduce the confidence in any potential biosignature observations linked to these biospheres.
3D simulations of TRAPPIST-1e with varying CO2, CH4, and haze profiles
Monthly Notices of the Royal Astronomical Society, Volume 530, Issue 3, pp.2933-2933 (2024)
Abstract:
Using a 3D General Circulation Model, the Unified Model, we present results from simulations of a tidally locked TRAPPIST-1e with varying carbon dioxide CO2 and methane CH4 gas concentrations, and their corresponding prescribed spherical haze profiles. Our results show that the presence of CO2 leads to a warmer atmosphere globally due to its greenhouse effect, with the increase of surface temperature on the dayside surface reaching up to ∼14.1 K, and on the nightside up to ∼21.2 K. Increasing presence of CH4 first elevates the surface temperature on the dayside, followed by a decrease due to the balance of tropospheric warming and stratospheric cooling. A thin layer of haze, formed when the partial pressures of CH4 to CO2 (pCH4/pCO2) = 0.1, leads to a dayside warming of ∼4.9 K due to a change in the water vapour H2O distribution. The presence of a haze layer that formed beyond the ratio of 0.1 leads to dayside cooling. The haze reaches an optical threshold thickness when pCH4/pCO2 ∼ 0.4 beyond which the dayside mean surface temperature does not vary much. The planet is more favourable to maintaining liquid water on the surface (mean surface temperature above 273.15 K) when pCO2 is high, pCH4 is low, and the haze layer is thin. The effect of CO2, CH4, and haze on the dayside is similar to that for a rapidly rotating planet. On the contrary, their effect on the nightside depends on the wind structure and the wind speed in the simulation
Modeling Atmospheric Lines by the Exoplanet Community (MALBEC) Version 1.0: A CUISINES Radiative Transfer Intercomparison Project
The Planetary Science Journal, Volume 5, Issue 3, id.64, 15 pp (2024)
Abstract:
Radiative transfer (RT) models are critical in the interpretation of exoplanetary spectra, in simulating exoplanet climates, and when designing the specifications of future flagship observatories. However, most models differ in methodologies and input data, which can lead to significantly different spectra. In this paper, we present the experimental protocol of the Modeling Atmospheric Lines By the Exoplanet Community (MALBEC) project. MALBEC is an exoplanet model intercomparison project that belongs to the Climates Using Interactive Suites of Intercomparisons Nested for Exoplanet Studies framework, which aims to provide the exoplanet community with a large and diverse set of comparison and validation of models. The proposed protocol tests include a large set of initial participating RT models, a broad range of atmospheres (from hot Jupiters to temperate terrestrials), and several observation geometries, which would allow us to quantify and compare the differences between different RT models used by the exoplanetary community. Two types of tests are proposed: transit spectroscopy and direct imaging modeling, with results from the proposed tests to be published in dedicated follow-up papers. To encourage the community to join this comparison effort and as an example, we present simulation results for one specific transit case (GJ-1214 b), in which we find notable differences in how the various codes handle the discretization of the atmospheres (e.g., sub-layering), the treatment of molecular opacities (e.g., correlated-k, line-by-line) and the default spectroscopic repositories generally used by each model (e.g., HITRAN, HITEMP, ExoMol).
3D Simulations of the Archean Earth Including Photochemical Haze Profiles
Journal of Geophysical Research: Atmospheres, Volume 128, Issue 20 (2023)
Abstract:
We present results from 3D simulations of the Archean Earth including a prescribed (non-interactive) spherical haze generated through a 1D photochemical model. Our simulations suggest that a thin haze layer, formed when CH4/CO2 = 0.1, leads to global warming of ∼10.6 K due to the change of water vapor and cloud feedback, compared to the simulation without any haze. However, a thicker haze layer, formed when CH4/CO2 > 0.1, leads to global cooling of up to ∼65 K as the scattering and absorption of shortwave radiation from the haze reduces the radiation from reaching the planetary surface. A thermal inversion is formed with a lower tropopause as the CH4/CO2 ratio increases. The haze reaches an optical threshold thickness when CH4/CO2 ∼ 0.175 beyond which the atmospheric structure and the global surface temperature do not vary much.