A critical question in astrobiology is whether exo-Earth candidates (EECs) are Earth-like, in that they originate life that progressively oxygenates their atmospheres similarly to Earth. We propose answering this question statistically by searching for O2 and O3 on EECs with missions such as HabEx or LUVOIR. We explore the ability of these missions to constrain the fraction, f E, of EECs that are Earth-like in the event of a null detection of O2 or O3 on all observed EECs. We use the Planetary Spectrum Generator to simulate observations of EECs with O2 and O3 levels based on Earth’s history. We consider four instrument designs—LUVOIR-A (15 m), LUVOIR-B (8 m), HabEx with a starshade (4 m, “HabEx/SS”), and HabEx without a starshade (4 m, “HabEx/no-SS”)—as well as three estimates of the occurrence rate of EECs (η earth): 24%, 5%, and 0.5%. In the case of a null detection, we find that for η earth = 24%, LUVOIR-A, LUVOIR-B, and HabEx/SS would constrain f E to ≤0.094, ≤0.18, and ≤0.56, respectively. This also indicates that if f E is greater than these upper limits, we are likely to detect O3 on at least one EEC. Conversely, we find that HabEx/no-SS cannot constrain f E, due to the lack of a coronagraph ultraviolet channel. For η earth = 5%, only LUVOIR-A and LUVOIR-B would be able to constrain f E, to ≤0.45 and ≤0.85, respectively. For η earth = 0.5%, none of the missions would allow us to constrain f E, due to the low number of detectable EECs. We conclude that the ability to constrain f E is more robust to uncertainties in η earth for missions with larger aperture mirrors. However, all missions are susceptible to an inconclusive null detection if η earth is sufficiently low.
A rigorous definition of the habitable zone and its dependence on planetary properties is part of the search for habitable exoplanets. In this work, we use the general circulation model ExoCAM to determine how the inner edge of the habitable zone of tidally locked planets orbiting M dwarf stars depends on planetary radius, surface gravity, and surface pressure. We find that the inner edge of the habitable zone for more massive planets occurs at higher stellar irradiation, as found in previous one-dimensional simulations. We also determine the relative effects of varying planetary radius and surface gravity. Increasing the planetary radius leads to a lower planetary albedo and warmer climate, pushing the inner edge of the habitable zone to lower stellar irradiation. This results from a change in circulation regime that leads to the disruption of the thick, reflective cloud deck around the substellar point. Increasing gravity increases the outgoing longwave radiation, which moves the inner edge of the habitable zone to higher stellar irradiation. This is because the column mass of water vapor decreases with increasing gravity, leading to a reduction in the greenhouse effect. The effect of gravity on the outgoing longwave radiation is stronger than the effect of radius on the planetary albedo, so that increasing gravity and radius together causes the inner edge of the habitable zone to move to higher stellar irradiation. Our results show that the inner edge of the habitable zone for more massive terrestrial planets occurs at a larger stellar irradiation.
A terrestrial planet’s rotation period is one of the key parameters that determines its climate and habitability. Current methods for detecting the rotation period of exoplanets are not suitable for terrestrial exoplanets. Here we demonstrate that, under certain conditions, the rotation period of an Earth-like exoplanet will be detectable using direct-imaging techniques. We use a global climate model that includes clouds to simulate reflected starlight from an Earth-like exoplanet and explore how different parameters (e.g., orbital geometry, wavelength, time resolution) influence the detectability of the planet’s rotation period. We show that the rotation period of an Earth-like exoplanet is detectable using visible-wavelength channels with time-series monitoring at a signal-to-noise ratio (S/N) >20 with ∼5–15 rotation periods of data, while the rotation period of a planet with full ocean coverage is unlikely to be detectable. To better detect the rotation period, one needs to plan the observation so that each individual integration would yield a S/N >10, while keeping the integration time shorter than 1/6 to 1/4 of the rotation period of the planet. Our results provide important guidance for rotation period detection of Earth-like exoplanets in reflected light using future space telescopes.
About 4000 exoplanets have been confirmed since the year of 1992, and for most of the planets, the main parameters that can be measured are planetary radius and mass.Based on these two parameters, surface gravity can be estimated. In this work, we investigate the effects of varying radius and gravity on the climate of rapidly rotating terrestrial planets with assuming they have an ocean and Earth-like atmospheres (N 2 , CO 2 , and H 2 O). Using a three-dimensional (3D) atmospheric general circulation model (GCM), we find that varying radius mainly influences the equator-to-pole surface temperature difference while varying gravity mainly influences the mean surface temperature. For planets of larger radii, the meridional atmospheric energy transport is weaker, which warms the tropics but cools high latitudes. For planets of larger gravities, the surface is globally cooler due to the fact that saturated vapor pressure depends on air temperature only and column water vapor mass is approximately equal to saturated vapor pressure over gravity multiplied by relative humidity. The relative humidity does not change much in our experiments. Ice albedo and water vapor feedbacks act to further amplify the effects of varying radius and gravity. These results suggest that radius and gravity are important factors for planetary climate, although
Based on the sensitivity of oysters to water environmental factors, a hydrodynamic model in Tongzhou Bay, southwest of China’s Yellow Sea, is set up to analyse the impact of the hydrodynamic and suspended sediment on the Liyashan Oyster Reef. The results show that the hydrodynamic characteristics of the waters near the oyster reef will not be significantly affected by the implementation of the project. The diffusion range of suspended sediment concentration greater than 10mg/L caused by channel dredging will not reach and affect oyster reef area, and the growth of oysters will not be significantly affected by Tongzhou Bay Channel Construction.
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