scholarly journals The atmospheres of rocky exoplanets

2020 ◽  
Vol 636 ◽  
pp. A71 ◽  
Author(s):  
O. Herbort ◽  
P. Woitke ◽  
Ch. Helling ◽  
A. Zerkle
Keyword(s):  
Gas Phase ◽  
Simultaneous Detection ◽  
Atmospheric Composition ◽  
Rock Composition ◽  
Metal Hydroxides ◽  
Element Abundances ◽  
Bulk Silicate Earth ◽  
Molecular Features ◽  
Future Space ◽  
Different Parts

Context. Little is known about the interaction between atmospheres and crusts of exoplanets so far, but future space missions and ground-based instruments are expected to detect molecular features in the spectra of hot rocky exoplanets. Aims. We aim to understand the composition of the gas in an exoplanet atmosphere which is in equilibrium with a planetary crust. Methods. The molecular composition of the gas above a surface made of a mixture of solid and liquid materials was determined by assuming phase equilibrium for given pressure, temperature, and element abundances. We study total element abundances that represent different parts of the Earth’s crust (continental crust, bulk silicate Earth, mid oceanic ridge basalt), CI chondrites and abundances measured in polluted white dwarfs. Results. For temperatures between ~600 and ~3500 K, the near-crust atmospheres of all considered total element abundances are mainly composed of H2O, CO2, and SO2 and in some cases of O2 and H2. For temperatures ≲500 K, only N2-rich or CH4-rich atmospheres remain. For ≳3500 K, the atmospheric gas is mainly composed of atoms (O, Na, Mg, and Fe), metal oxides (SiO, NaO, MgO, CaO, AlO, and FeO), and some metal hydroxides (KOH and NaOH). The inclusion of phyllosilicates as potential condensed species is crucial for lower temperatures, as they can remove water from the gas phase below about 700 K and inhibit the presence of liquid water. Conclusions. Measurements of the atmospheric composition could, in principle, characterise the rock composition of exoplanet crusts. H2O, O2 and CH4 are natural products from the outgassing of different kinds of rocks that had time to equilibrate. These are discussed as biomarkers, but they do emerge naturally as a result of the thermodynamic interaction between the crust and atmosphere. Only the simultaneous detection of all three molecules might be a sufficient biosignature, as it is inconsistent with chemical equilibrium.

scholarly journals A Sensitive Spectral Survey of Interstellar Features in the Near-UV [3040-3700Å]

2013 ◽  
Vol 9 (S297) ◽  
pp. 58-63
Author(s):  
N. H. Bhatt ◽  
J. Cami
Keyword(s):  
Gas Phase ◽  
Signal To Noise Ratio ◽  
Fundamental Parameters ◽  
Molecular Features ◽  
Polycyclic Aromatic ◽  
Early Type Stars ◽  
The Individual ◽  
Spectral Survey ◽  
Absorption Features ◽  
Uv Range

AbstractWe present a comprehensive and sensitive unbiased survey of interstellar features in the near-UV range (3040-3700 Å). We combined a large number of VLT/UVES archival observations of a sample of highly reddened early type stars – typical diffuse interstellar band (DIB) targets. We stacked the individual observations to obtain a spectrum with a signal-to-noise ratio exceeding 1500. Careful inspection of this spectrum reveals tens of absorption features of interstellar nature, most of which can be identified with various atomic and molecular features. We furthermore detect four weak unidentified features, but we cannot establish their interstellar nature. Our sensitivity is limited by telluric and instrumental residuals; this precludes us from detecting broader features (e.g. DIBs). For each detected feature, we measured fundamental parameters (radial velocities, line widths, and equivalent widths). We also compare our co-added spectrum to cold gas-phase laboratory measurements of small, neutral polycyclic aromatic hydrocarbon (PAH) molecules.

scholarly journals Atmospheric gas-phase composition over the Indian Ocean

2020 ◽  
Author(s):  
Susann Tegtmeier ◽  
Christa Marandino ◽  
Yue Jia ◽  
Birgit Quack ◽  
Anoop S. Mahajan
Keyword(s):  
Phase Composition ◽  
Indian Ocean ◽  
Greenhouse Gases ◽  
Gas Phase ◽  
Winter Monsoon ◽  
Atmospheric Composition ◽  
Trace Gas ◽  
Monsoon Circulation ◽  
Gangetic Plain ◽  
The Indian Ocean

Abstract. The Indian Ocean is coupled to atmospheric dynamics, transport and chemical composition via several unique mechanisms, such as the seasonally varying monsoon circulation. During the winter monsoon season, high pollution levels are regularly observed over the entire northern Indian Ocean, while during the summer monsoon, clean air dominates the atmospheric composition, leading to distinct chemical regimes. The changing atmospheric composition over the Indian Ocean can interact with oceanic biogeochemical cycles and impact marine ecosystems, resulting in potential climate feedbacks. Here, we review current progress in detecting and understanding atmospheric gas-phase composition over the Indian Ocean and its local and global impacts. The review takes into account results from recent Indian Ocean ship campaigns, satellite measurements, station data and information on continental and oceanic trace gas emissions. The distribution of all major pollutants and greenhouse gases shows pronounced differences between the landmass source regions and the Indian Ocean with strong gradients over the coastal areas. Surface pollution and ozone are highest during the winter monsoon over the Bay of Bengal and the Arabian Sea coastal waters due to air mass advection from the Indo-Gangetic Plain and continental outflow from Southeast Asia. We observe, however, that unusual types of wind patterns can lead to pronounced deviations of the typical trace gas distributions. For example, the ozone distribution maxima shift to different regions under different wind scenarios. The distribution of greenhouse gases over the Indian Ocean shows many similarities when compared to the pollution fields, but also some differences of the latitudinal and seasonal variations resulting from their long lifetimes and biogenic sources. Mixing ratios of greenhouse gases such as methane show positive trends over the Indian Ocean, but long-term changes of pollution and ozone, and in particular how they are driven by changing emissions and transport patterns, require further investigation in the future. Although we know that changing atmospheric composition and perturbations within the Indian Ocean affect each other, the impacts of atmospheric pollution on oceanic biogeochemistry and trace gas cycling is severely understudied. We highlight potential mechanisms, future research topics and observational requirements that need to be explored in order to fully understand interactions and feedbacks between the ocean and atmosphere in the Indian Ocean region.

scholarly journals Phase Coexistence and Structural Dynamics of Redox Metal Catalysts Revealed by Operando TEM

2021 ◽  
Author(s):  
Xing Huang ◽  
Travis Jones ◽  
Alexey Fedorov ◽  
Ramzi Farra ◽  
Christophe Copéret ◽  
...  
Keyword(s):  
Gas Phase ◽  
Structural Dynamics ◽  
Redox Reactions ◽  
Active Sites ◽  
Chemical Potential ◽  
Hydrogen Oxidation ◽  
Simultaneous Detection ◽  
Metal Catalysts ◽  
Operating Conditions ◽  
Chemical Dynamics

<div>Metal catalysts play an important role in industrial redox reactions. Although extensively studied, the state of these catalysts under operating conditions is largely unknown and assignments of active sites remain speculative. Herein, we present an operando transmission electron microscopy study that interrelates structural dynamics of redox metal catalysts to their activity. Using hydrogen oxidation on copper as an elementary redox reaction, we reveal how the interaction between metal and surrounding gas phase induces complex structural transformations and drives the system from a thermodynamic equilibrium towards a state controlled by chemical dynamics. Direct imaging combined with the simultaneous detection of catalytic activity provides unparalleled structureactivity insights that identify distinct mechanisms for water formation and reveals the means by which the system self-adjusts to changes of the gas phase chemical potential. Density function theory calculations show that surface phase transitions are driven by chemical dynamics even when the system is far from a thermodynamic phase boundary. In a bottom-up approach, the dynamic behavior observed here for an elementary reaction is finally extended to more relevant redox reactions and other metal catalysts, which underlines the importance of chemical dynamics for the formation and constant re-generation of transient active sites during catalysis. <br></div>

scholarly journals FORest canopy atmosphere transfer (FORCAsT) 1.0: a 1-D model of biosphere–atmosphere chemical exchange

2015 ◽  
Vol 8 (7) ◽  
pp. 5183-5234
Author(s):  
K. Ashworth ◽  
S. H. Chung ◽  
R. J. Griffin ◽  
J. Chen ◽  
R. Forkel ◽  
...  
Keyword(s):  
Gas Phase ◽  
Forest Canopy ◽  
Chemical Exchange ◽  
Critical Role ◽  
Mixed Forest ◽  
Oxidation Products ◽  
Atmospheric Composition ◽  
Alkyl Nitrate ◽  
Key Species ◽  
The Impact

Abstract. Biosphere-atmosphere interactions play a critical role in governing atmospheric composition, mediating the concentration of key species such as ozone and aerosol, thereby influencing air quality and climate. The exchange of reactive trace gases and their oxidation products (both gas and particle phase) is of particular importance in this process. The FORCAsT (FORest Canopy AtmoSphere Transfer) one-dimensional model is developed to study the emission, deposition, chemistry and transport of volatile organic compounds (VOCs) and their oxidation products in the atmosphere within and above the forest canopy. We include an equilibrium partitioning scheme, making FORCAsT one of the few canopy models currently capable of simulating the formation of secondary organic aerosols (SOA) from VOC oxidation in a forest environment. We evaluate the capability of FORCAsT to reproduce observed concentrations of key gas-phase species and report modeled SOA concentrations within and above a mixed forest at the University of Michigan Biological Station (UMBS) during the Community Atmosphere-Biosphere Interactions Experiment (CABINEX) field campaign in summer 2009. We examine the impact of two different gas-phase chemical mechanisms on modelled concentrations of short-lived primary emissions, such as isoprene and monoterpenes, and their oxidation products. While the two chemistry schemes perform similarly under high-NOx conditions, they diverge at the low levels of NOx at UMBS. We identify peroxy radical and alkyl nitrate chemistry as the key causes of the differences, highlighting the importance of this chemistry in understanding the fate of biogenic VOCs (bVOCs) for both the modelling and measurement communities.

Alfnoor: a population study on Ariel's low resolution transmission spectra.

2021 ◽  
Author(s):  
Lorenzo V. Mugnai ◽  
Ahmed Al-Refaie ◽  
Andrea Bocchieri ◽  
Quentin Changeat ◽  
Enzo Pascale ◽  
...  
Keyword(s):  
Machine Learning Algorithms ◽  
Atmospheric Composition ◽  
Transmission Spectra ◽  
Low Resolution ◽  
Scientific Content ◽  
Data Set ◽  
Target List ◽  
Spectroscopic Observations ◽  
Molecular Features ◽  
Reconnaissance Survey

&lt;p&gt;In the next decade, the Ariel Space Telescope will provide the first statistical data set of exoplanet spectra, performing spectroscopic observations of about 1000 exoplanets in the wavelength range 0.5 - 7.8 micron during its Reconnaissance Survey. The Ariel Reconnaissance Survey has been designed specifically to identify planets without molecular features in their atmosphere, and select targets (about 500) for accurate chemical characterisation with higher SNR spectroscopic observations.&lt;/p&gt; &lt;p&gt;In this work, we investigate the information content of Ariel's Reconnaissance Survey low resolution transmission spectra. We produce different planetary populations using the Ariel candidate target list, randomizing the planetary atmospheres, and simulating the Ariel observations using the Alfnoor software. Then we analyse the dataset, getting three different results:&lt;/p&gt; &lt;p&gt;(1) We present a solid strategy that will allow selecting candidate planets to be reobserved in an Ariel's higher resolution, using a chi-squared based metric to identify the flat spectra.&lt;/p&gt; &lt;p&gt;(2) Because the reconnaissance survey is not optimised for spectral retrieval, we propose a novel model-independent metric to preliminary classify exoplanets by their atmospheric composition. Without any other planetary information than the spectrum, our metric proves capable of indicating the presence of a molecule when its abundance in the atmosphere is in excess of 10&lt;sup&gt;-4&lt;/sup&gt; in mixing ratio.&lt;/p&gt; &lt;p&gt;(3) We introduce the possibility of finding other methods to better exploit the data scientific content. We report as an example of possible strategies, a preliminary study involving Deep and Machine Learning algorithms. We show that their performance in identifying the presence of a certain molecule in the spectra is marginally better than our metric for some of these algorithms, while others outperform the metric.&amp;#160;&lt;/p&gt; &lt;p&gt;We conclude that the the Ariel reconnaissance survey is effective in detecting exoplanets manifesting featureless spectra, and we further show that the data collected in this observing mode have a rich scientific content, allowing for a first chemical classification of the observed targets.&lt;/p&gt;

Laser-Induced Fluorescence Measurement of Free Radical Intermediates

1988 ◽  
Vol 117 ◽  
Author(s):  
David R. Crosley
Keyword(s):  
Free Radicals ◽  
Gas Phase ◽  
Spectroscopic Method ◽  
Simultaneous Detection ◽  
Reactive Intermediates ◽  
Laser Induced Fluorescence ◽  
Materials Processing ◽  
Fluorescence Measurement ◽  
Radical Intermediates ◽  
Quantitative Measurements

AbstractLaser-induced fluorescence (LIF) provides a means for sensitive, selective and nonintrusive measurements of reactive intermediates, often free radicals, which control the chemistry of combustion. The same approach can be used to detect in the gas phase, atoms, radicals and ions which are reactive intermediates in materials processing. This article briefly examines the use of LIF in combustion. It includes a description of the LIF spectroscopic method as employed for quantitative measurements, and the use of LIF in a semiquantitative manner with extension to the simultaneous detection of more than one species.

scholarly journals Future Observations of Transits and Light Curves from Space

2008 ◽  
Vol 4 (S253) ◽  
pp. 319-328 ◽  
Author(s):  
Charles A. Beichman ◽  
Tom Greene ◽  
John Krist
Keyword(s):  
Thermal Structure ◽  
Light Curves ◽  
Atmospheric Composition ◽  
Light Curve Analysis ◽  
James Webb Space Telescope ◽  
Sky Survey ◽  
Future Space ◽  
Host Stars

AbstractA variety of new observational opportunities have made transit and more generally light curve analysis central to the study of exoplanets. Talks at this IAU 253 Symposium have dramatically highlighted the measurement of the radius, density, atmospheric composition and atmospheric thermal structure, presently for relatively large, hot planets, but soon for smaller planets orbiting further from their host stars. On-going and future space observations will play a key role in the detection and characterization of these planetary systems. After a brief review, I focus on two topics: the need for a sensitive all-sky survey for planets transiting the brightest, closest stars and the follow-up opportunities afforded by the James Webb Space Telescope (JWST).

scholarly journals Phase Coexistence and Structural Dynamics of Redox Metal Catalysts Revealed by Operando TEM

2021 ◽  
Author(s):  
Xing Huang ◽  
Travis Jones ◽  
Alexey Fedorov ◽  
Ramzi Farra ◽  
Christophe Copéret ◽  
...  
Keyword(s):  
Gas Phase ◽  
Structural Dynamics ◽  
Redox Reactions ◽  
Active Sites ◽  
Chemical Potential ◽  
Hydrogen Oxidation ◽  
Simultaneous Detection ◽  
Metal Catalysts ◽  
Operating Conditions ◽  
Chemical Dynamics

<div>Metal catalysts play an important role in industrial redox reactions. Although extensively studied, the state of these catalysts under operating conditions is largely unknown and assignments of active sites remain speculative. Herein, we present an operando transmission electron microscopy study that interrelates structural dynamics of redox metal catalysts to their activity. Using hydrogen oxidation on copper as an elementary redox reaction, we reveal how the interaction between metal and surrounding gas phase induces complex structural transformations and drives the system from a thermodynamic equilibrium towards a state controlled by chemical dynamics. Direct imaging combined with the simultaneous detection of catalytic activity provides unparalleled structureactivity insights that identify distinct mechanisms for water formation and reveals the means by which the system self-adjusts to changes of the gas phase chemical potential. Density function theory calculations show that surface phase transitions are driven by chemical dynamics even when the system is far from a thermodynamic phase boundary. In a bottom-up approach, the dynamic behavior observed here for an elementary reaction is finally extended to more relevant redox reactions and other metal catalysts, which underlines the importance of chemical dynamics for the formation and constant re-generation of transient active sites during catalysis. <br></div>

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