Dynamic and isotopic evolution of ice reservoirs on Mars

Vos, E.; Aharonson, O.; Schörghofer, N.

doi:10.1016/j.icarus.2019.01.018

Cited by 18 publications

(32 citation statements)

References 38 publications

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“…Similar calculations could be performed for other atmospheric compositions. One interesting possible application is the atmosphere of Mars, where scientists are beginning to use isotopic information to study the planet's water cycle (Krasnopolsky, 2015; Montmessin et al., 2005; Vos et al., 2019) but so far have not included diffusion fractionation in their models. The required calculations for the diffusion of water isotopes in CO 2 could be performed with the recent H 2 O–CO 2 pair potential of Hellmann (2019b).…”

Section: Discussionmentioning

confidence: 99%

First‐Principles Diffusivity Ratios for Kinetic Isotope Fractionation of Water in Air

Hellmann

Harvey

2020

Geophysical Research Letters

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Kinetic isotope fractionation between water vapor and liquid water or ice depends on the ratio of the diffusivities of the isotopic species in air, but there is disagreement as to the values of these ratios and limited information about their temperature dependence. We use state-of-the-art intermolecular potential-energy surfaces for the water-nitrogen and water-oxygen pairs, along with the kinetic theory of molecular gases, to calculate from first principles the diffusivities of water isotopologues in air. The method has sufficient precision to produce accurate diffusivity ratios. For the HDO/H 2 O ratio, we find that the often used hard-sphere kinetic theory is significantly in error and confirm the 1978 experimental result of Merlivat. For the ratios involving 17 O and 18 O, the simple kinetic theory is relatively close to our more rigorous results. We provide diffusivity ratios from 190 K to 500 K, greatly expanding the range of temperatures for which these ratios are available. Plain Language Summary The different isotopes of hydrogen and oxygen distribute unevenly between water vapor and liquid or solid water during evaporation or precipitation. This fractionation of isotopes is widely used in studies of climate and other geophysical processes. Part of the fractionation depends on the relative diffusion rates of the isotopic molecules in air, but these relative diffusivities are difficult to measure and existing data are inconsistent. Because of these inconsistencies, a simple theory that treats the molecules as hard spheres is often used. We used more rigorous theory based on detailed quantum-mechanical description of the interactions between water molecules and those of nitrogen and oxygen to calculate the diffusivity ratios. Our results confirm some previous experiments and show that the simple hard-sphere model is not accurate. They also provide diffusivity ratios at temperatures where no experimental data exist, such as those relevant to ice.

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Section: Discussionmentioning

confidence: 99%

First‐Principles Diffusivity Ratios for Kinetic Isotope Fractionation of Water in Air

Hellmann

Harvey

2020

Geophysical Research Letters

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“…Earth is not the only place in our solar system with a hydrologic cycle. The distribution and seasonal variation of isotopic water species (especially HDO) has been used to study the climate of Mars (Encrenaz et al., 2016; Krasnopolsky, 2015; Montmessin et al., 2005; Villanueva et al., 2015; Vos et al., 2019). Current modeling of isotopic cycles on Mars neglects kinetic fractionation (Montmessin et al., 2005).…”

Section: Introductionmentioning

confidence: 99%

“…• Kinetic isotope fractionation depends on diffusivity ratios that have not been measured for conditions corresponding to Mars or Titan • The relative diffusivity of isotopologues can be calculated as a function of temperature from highaccuracy intermolecular potentials • Rigorous results agree well with simpler kinetic theory for water on Mars, but less well for methane on Titan Krasnopolsky, 2015;Montmessin et al, 2005;Villanueva et al, 2015;Vos et al, 2019). Current modeling of isotopic cycles on Mars neglects kinetic fractionation (Montmessin et al, 2005).…”

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confidence: 98%

First‐Principles Diffusivity Ratios for Atmospheric Isotope Fractionation on Mars and Titan

Hellmann

Harvey

2021

JGR Planets

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On Earth, the fractionation of stable water isotopes such as HDO and 18 2 H O is important for understanding the hydrologic cycle (Gat, 1996). In addition to the equilibrium fractionation that occurs between water vapor and ice or liquid water, in some cases a significant role is played by kinetic fractionation that depends on the ratio of the atmospheric diffusivity of the isotopologue of interest to that of H 2 O. Recently, we reported temperature-dependent diffusivity ratios in air calculated from the kinetic theory of molecular gases applied to state-of-the-art intermolecular potentials based on ab initio calculations for the interaction between water and molecular nitrogen and oxygen (Hellmann & Harvey, 2020). We found that, especially for HDO, the often-assumed constant diffusivity ratios from simple hard-sphere kinetic theory were in error, and that the temperature dependence of the diffusivity ratios was not negligible. We supplied recommended diffusivity ratios and their uncertainties from 190 to 500 K, greatly exceeding the range in which the (scattered) experimental data exist.Earth is not the only place in our solar system with a hydrologic cycle. The distribution and seasonal variation of isotopic water species (especially HDO) has been used to study the climate of Mars (Encrenaz Abstract Recent work used the kinetic theory of molecular gases, along with state-of-the-art intermolecular potentials, to calculate from first principles the diffusivity ratios necessary for modeling kinetic fractionation of water isotopes in air. Here, we extend that work to the Martian atmosphere, employing potential-energy surfaces for the interaction of water with carbon dioxide and with nitrogen. We also derive diffusivity ratios for methane isotopes in the atmosphere of Titan by using a highquality potential for the methane-nitrogen pair. The Mars calculations cover 100-400 K, while the Titan calculations cover 50-200 K. Surprisingly, the simple hard-sphere theory that is inaccurate for Earth's atmosphere is in good agreement with the rigorous results for the diffusion of water isotopes in the Martian atmosphere. A modest disagreement with the hard-sphere results is observed for the diffusivity ratio of CH 3 D in the atmosphere of Titan. We present temperature-dependent correlations, as well as estimates of uncertainty, for the diffusivity ratios involving HDO, H 2 17 O, and H 2 18 O in the Martian atmosphere, and for CH 3 D and 13 CH 4 in the atmosphere of Titan, providing for the first time the necessary data to be able to model kinetic isotope fractionation in these environments.Plain Language Summary Different isotopes distribute unevenly between the vapor phase and liquid or solid phases during precipitation and evaporation, and the resulting changes in isotope ratios are used in the study of climate and other geophysical processes. While equilibrium aspects of this fractionation are fairly well understood, in some circumstances there is also a kinetic component that depends on the relative diffusivities of diffe...

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“…Even though multiple sources likely supplied the atmospheric water vapor that contributed to deposition in the PLDs, finding the ratio of D/H within solid ice will provide insight into the long-term (>3 Ga) climate history of Mars (Vos et al, 2019). This in turn will teach us about the loss rate of water to space (Jakosky 1990) and Mars' earlier environment.…”

Section: Isotope Variability In Layersmentioning

confidence: 98%

“…The seasonal signal of D/H from atmosphere-ice exchange in the northern hemisphere imparts a distinctive isotopic signature in the atmosphere of >1000 per mil (Villanueva et al, 2015) that may be recorded in the currently forming ice layer. Over time, and through orbital cycles, the D/H ratio of layered ice will vary based on the source reservoirs that supply the materials (Vos et al, 2019). This deposition can tell us about the climate signal of orbital parameters driving variations in obliquity, which in turn provides information on what reservoirs are accessed at different orbital states (e.g., Montmessin et al, 2005;Fisher 2007).…”

Section: Isotope Variability In Layersmentioning

confidence: 99%

The Holy Grail: A road map for unlocking the climate record stored within Mars’ polar layered deposits

Smith

Hayne

Byrne

et al. 2020

Planetary and Space Science

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Dynamic and isotopic evolution of ice reservoirs on Mars

Cited by 18 publications

References 38 publications

First‐Principles Diffusivity Ratios for Kinetic Isotope Fractionation of Water in Air

First‐Principles Diffusivity Ratios for Kinetic Isotope Fractionation of Water in Air

First‐Principles Diffusivity Ratios for Atmospheric Isotope Fractionation on Mars and Titan

The Holy Grail: A road map for unlocking the climate record stored within Mars’ polar layered deposits

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