Recently, Smirnov published a paper (B. M. Smirnov, "Collision and radiative processes in emission of atmospheric carbon dioxide", 2018, J. Phys. D.: Appl. Phys., Vol. 51, No. 21, pp. 214004) which dismisses the role of increasing concentrations of anthropogenic CO$_2$ on global warming of planet Earth. We show that these conclusions are the consequence of two flaws in Smirnov's theoretical model which neglect the effects of the increased concentrations of CO$_2$ on the absorption of Earth's blackbody radiation in the 12-15$μ$m region. The influence of doubling the concentration of CO$_2$ in the atmosphere on the surface temperature is not $Δ$T=0.02K, or even $Δ$T=0.4K if only one of the two mistakes in Smirnov's analysis is corrected. The correct value lies within $Δ$T=1.1-1.3K as outlined by other authors analysis using simplified, yet more theoretically consistent models.
Understanding the possible climatic conditions on rocky extrasolar planets, and thereby their potential habitability, is one of the major subjects of exoplanet research. Determining how the climate, as well as potential atmospheric biosignatures, change under different conditions is a key aspect when studying Earth-like exoplanets. One important property is the atmospheric mass hence pressure and its influence on the climatic conditions. Therefore, the aim of the present study is to understand the influence of atmospheric mass on climate, hence habitability, and the spectral appearance of plan…
Ozone is an important radiative trace gas in the Earth's atmosphere. The presence of ozone can significantly influence the thermal structure of an atmosphere, and by this e.g. cloud formation. Photochemical studies suggest that ozone can form in carbon dioxide-rich atmospheres. We investigate the effect of ozone on the temperature structure of simulated early Martian atmospheres. With a 1D radiative-convective model, we calculate temperature-pressure profiles for a 1 bar carbon dioxide atmosphere. Ozone profiles are fixed, parameterized profiles. We vary the location of the ozone layer maximum…
Context: The thermal and chemical structures of the upper atmospheres of planets crucially influence losses to space and must be understood to constrain the effects of losses on atmospheric evolution. Aims: We develop a 1D first-principles hydrodynamic atmosphere model that calculates atmospheric thermal and chemical structures for arbitrary planetary parameters, chemical compositions, and stellar inputs. We apply the model to study the reaction of the Earth's upper atmosphere to large changes in the CO$_2$ abundance and to changes in the input solar XUV field due to the Sun's activity evoluti…
We present new 3.6 and 4.5 micron secondary eclipse measurements for five cool (less than approximately 1000 K) transiting gas giant planets: HAT-P-15b, HAT-P-17b, HAT-P-18b, HAT-P-26b, and WASP-69b. We detect eclipses in at least one bandpass for all planets except HAT-P-15b. We confirm and refine the orbital eccentricity of HAT-P-17b, which is also the only planet in our sample with a known outer companion. We compare our measured eclipse depths in these two bands, which are sensitive to the relative abundances of methane versus carbon monoxide and carbon dioxide, respectively, to prediction…
Carbon dioxide (CO$_2$) ice clouds have been routinely observed in the middle atmosphere of Mars. However, there are still uncertainties concerning physical mechanisms that control their altitude, geographical, and seasonal distributions. Using the Max Planck Institute Martian General Circulation Model (MPI-MGCM), incorporating a state-of-the-art whole atmosphere subgrid-scale gravity wave parameterization [Yiğit et al., 2008], we demonstrate that internal gravity waves generated by lower atmospheric weather processes have wide reaching impact on the Martian climate. Globally, GWs cool the upp…
Most exoplanets detected so far have atmospheric T significantly higher than 300K. Often close to their star, they receive an intense UV photons flux that triggers important photodissociation processes. The T dependency of VUV absorption cross sections are poorly known, leading to an undefined uncertainty in atmospheric models. Similarly, data measured at low T similar to that of the high atmosphere of Mars, Venus, and Titan are often lacking. Our aim is to quantify the T dependency of the abs. cross section of important molecules in planetary atmospheres. We want to provide both high-resoluti…
We present a comprehensive study of the abundance of carbon dioxide in exoplanetary atmospheres in hot, hydrogen-dominated atmospheres. We construct novel analytical models of systems in chemical equilibrium that include carbon monoxide, carbon dioxide, water, methane and acetylene and relate the equilibrium constants of the chemical reactions to temperature and pressure via the tabulated Gibbs free energies. We prove that such chemical systems may be described by a quintic equation for the mixing ratio of methane. By examining the abundances of these molecules across a broad range of temperat…
Recent advances in the high sensitivity spectroscopy have made it possible, in combination with accurate theoretical predictions, to observe for the first time very weak electric quadrupole transitions in a polar polyatomic molecule of water. Here we present accurate theoretical predictions of the complete quadrupole ro-vibrational spectrum of a non-polar molecule CO$_2$, important in atmospheric and astrophysical applications. Our predictions are validated by recent cavity enhanced absorption spectroscopy measurements and are used to assign few weak features in the recent ExoMars ACS MIR spec…
Ocean planets are volatile rich planets, not present in our Solar System, which are thought to be dominated by deep, global oceans. This results in the formation of high-pressure water ice, separating the planetary crust from the liquid ocean and, thus, also from the atmosphere. Therefore, instead of a carbonate-silicate cycle like on the Earth, the atmospheric carbon dioxide concentration is governed by the capability of the ocean to dissolve carbon dioxide (CO2). In our study, we focus on the CO2 cycle between the atmosphere and the ocean which determines the atmospheric CO2 content. The atm…
Carbon dioxide is one of the major contributors to the radiative forcing, increasing both the temperature and the humidity of Earth's atmosphere. If the stellar irradiance increases and water becomes abundant in the stratosphere of an Earth-like planet, it will be dissociated and the resultant hydrogen will escape from the atmosphere. This state is called the moist greenhouse threshold (MGT). Using a global climate model (GCM) of intermediate complexity, we explore how to identify this state for different CO2 concentrations and including the radiative effect of atmospheric ozone for the first …
Carbonate precipitation in oceans is essential for the carbonate-silicate cycle (inorganic carbon cycle) to maintain temperate climates. By considering the thermodynamics of carbonate chemistry, we demonstrate that the ocean pH decreases by approximately 0.5 for a factor of 10 increase in the atmospheric carbon dioxide content. The upper and lower limits of ocean pH are within 1-4 of each other, where the upper limit is buffered by carbonate precipitation and defines the ocean pH when the carbon cycle operates. If the carbonate compensation depth (CCD) resides above the ocean floor, then carbo…
Escape of an early atmosphere from Titan, during which time NH3 could be converted by photolysis into the present N2 dominated atmosphere, is an important problem in planetary science. Recently Gilliam and Lerman (2014) estimated escape driven by the surface temperature and pressure, which we show gave loss rates that are orders of magnitude too large. Their model, related to Jeans escape from an isothermal atmosphere, was used to show that escape driven only by surface heating would deplete the atmospheric inventory of N for a suggested Titan accretion temperature of ~355 K. Therefore, they c…
Melott et al. [2016] suggest that individual solar proton events (SPEs) are detectable as nitrate ion spikes in ice cores. They use the high fluence, high energy (hard spectrum) SPE of 23 February 1956 to calculate an enhancement of HNO3 from the surface to 46 km that is equivalent to a ~120 ng cm-2 nitrate ion spike observed in the GISP2H ice core. The Melott et al. [2016] approach is fundamentally flawed, since it considers only the absolute column burden of SPE-produced nitrate and not the pre-existing nitrate in the stratosphere. Modeling studies supported by extensive observations [Duders…
The atmospheric temperatures of the ultra-hot Jupiter KELT-9b straddle the transition between gas giants and stars, and therefore between two traditionally distinct regimes of atmospheric chemistry. Previous theoretical studies assume the atmosphere of KELT-9b to be in chemical equilibrium. Despite the high ultraviolet flux from KELT-9, we show using photochemical kinetics calculations that the observable atmosphere of KELT-9b is predicted to be close to chemical equilibrium, which greatly simplifies any theoretical interpretation of its spectra. It also makes the atmosphere of KELT-9b, which …
Duderstadt et al. [2016b] comment that the Melott et al. [2016] study of nitrate formation by solar proton events (SPEs) and comparison with the ice core archive is "fundamentally flawed," because it does not include pre-existing HNO3 in the stratosphere. We show that they exaggerate both the enhancement predicted by our findings and pre-industrial HNO3 levels in their model, and fail to prove this assertion. Our feasibility study matched expected SPE nitrate production with ground truth measurements. It is not clear that their approach is more realistic and absence of a detailed mechanism doe…
Nitrogen dioxide (NO$_2$) on Earth today has biogenic and anthropogenic sources. During the COVID-19 pandemic, observations of global NO$_2$ emissions have shown significant decrease in urban areas. Drawing upon this example of NO$_2$ as an industrial byproduct, we use a one-dimensional photochemical model and synthetic spectral generator to assess the detectability of NO$_2$ as an atmospheric technosignature on exoplanets. We consider cases of an Earth-like planet around Sun-like, K-dwarf and M-dwarf stars. We find that NO$_2$ concentrations increase on planets around cooler stars due to less…
Exoplanet Proxima b will be an important laboratory for the search for extraterrestrial life for the decades ahead. Here we discuss the prospects of detecting carbon dioxide at 15 um using a spectral filtering technique with the Medium Resolution Spectrograph (MRS) mode of the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST). At superior conjunction, the planet is expected to show a contrast of up to 100 ppm with respect to the star. At a spectral resolving power of R=1790-2640, about 100 spectral CO2 features are visible within the 13.2-15.8 um (3B) band, which can be c…
The current explosion in detection and characterization of thousands of extrasolar planets from the Kepler mission, the Hubble Space Telescope, and large ground-based telescopes opens a new era in searches for Earth-analog exoplanets with conditions suitable for sustaining life. As more Earth-sized exoplanets are detected in the near future, we will soon have an opportunity to identify habitable worlds. Which atmospheric biosignature gases from habitable planets can be detected with our current capabilities? The detection of the common biosignatures from nitrogen-oxygen rich terrestrial-type e…
The M-type star Gliese 581 is orbited by at least one terrestrial planet candidate in the habitable zone, i.e. GL 581 d. Orbital simulations have shown that additional planets inside the habitable zone of GL 581 would be dynamically stable. Recently, two further planet candidates have been claimed, one of them in the habitable zone. In view of the ongoing search for planets around M stars which is expected to result in numerous detections of potentially habitable Super-Earths, we take the GL 581 system as an example to investigate such planets. In contrast to previous studies of habitability i…
Of the 342 planets discovered so far orbiting other stars, 58 "transit" the stellar disk, meaning that they can be detected by a periodic decrease in the starlight flux. The light from the star passes through the atmosphere of the planet, and in a few cases the basic atmospheric composition of the planet can be estimated. As we get closer to finding analogues of Earth, an important consideration toward the characterization of exoplanetary atmospheres is what the transmission spectrum of our planet looks like. Here we report the optical and near-infrared transmission spectrum of the Earth, obta…
A Clearer View of HAT-P-1 b: JWST NIRSpec G395H Reveals Water, Carbon Dioxide, and Possibly Hydrogen Sulfide
Johns Hopkins University Applied Physics Laboratory（约翰斯·霍普金斯大学应用物理实验室）；William H. Miller III Department of Physics and Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学威廉·H·米勒三世物理与天文学系）；School of Earth & Planetary Sciences, National Institute of Science Education and Research (NISER)（国家科学教育与研究研究所地球与行星科学学院）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；Morton K. Blaustein Department of Earth & Planetary Sciences, Johns Hopkins University（约翰斯·霍普金斯大学莫顿·K·布拉斯坦地球与行星科学学院）；Space Telescope Science Institute（太空望远镜科学研究所）；School of Earth and Space Exploration, Arizona State University（亚利桑那州立大学地球与空间探索学院）；Department of Astrophysical Sciences, Princeton University（普林斯顿大学天体物理科学系）；Atmospheric, Oceanic, and Planetary Physics, University of Oxford（牛津大学大气、海洋与行星物理系）；Department of Physics and Astronomy, University of Exeter（埃克塞特大学物理与天文学系）
本研究结合 JWST、HST 的多波段光谱数据，证实热木星 HAT-P-1 b 大气富含水、二氧化碳，可能含硫化氢，金属丰度约为太阳的 10 倍，是热木星大气研究的基准天体。
Motivated by the work of Cooper & Showman, we revisit the chemical relaxation method, which seeks to enhance the computational efficiency of chemical-kinetics calculations by replacing the chemical network with a handful of independent source/sink terms. Chemical relaxation solves the evolution of the system and can treat disequilibrium chemistry, as the source/sink terms are driven towards chemical equilibrium on a prescribed chemical timescale, but it has surprisingly never been validated. First, we generalize the treatment by forgoing the use of a single chemical timescale, instead developi…
The origin of life on Earth involves the early appearance of an information-containing molecule such as RNA. The basic building blocks of RNA could have been delivered by carbon-rich meteorites, or produced in situ by processes beginning with the synthesis of hydrogen cyanide (HCN) in the early Earth's atmosphere. Here, we construct a robust physical and non-equilibrium chemical model of the early Earth atmosphere. The atmosphere is supplied with hydrogen from impact degassing of meteorites, sourced with water evaporated from the oceans, carbon dioxide from volcanoes, and methane from undersea…
A number of transiting, potentially habitable Earth-sized exoplanets have recently been detected around several nearby M dwarf stars. These worlds represent important targets for atmospheric characterization for the upcoming NASA James Webb Space Telescope. Given that available time for exoplanet characterization will be limited, it is critically important to first understand the capabilities and limitations of JWST when attempting to detect atmospheric constituents for potentially Earth-like worlds orbiting cool stars. Here, we explore coupled climate-chemistry atmospheric models for Earth-li…
The aim of the present work is to study the potential short-term atmospheric and biospheric influence of Gamma Ray Bursts on the Earth. We focus in the ultraviolet flash at the planet's surface, which occurs as a result of the retransmission of the $γ$ radiation through the atmosphere. This would be the only important short-term effect on life. We mostly consider Archean and Proterozoic eons, and for completeness we also comment on the Phanerozoic. Therefore, in our study we consider atmospheres with oxygen levels ranging from $10^{-5}$ to 1% of the present atmospheric level, representing diff…
