Mass fractionation in hydrodynamic escape

Hunten, D. M.; Pepin, R. O.; Walker, James C. G.

doi:10.1016/0019-1035(87)90022-4

Cited by 333 publications

(270 citation statements)

References 31 publications

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“…The cross-over mass equation given by Hunten et al [41] can be used to derive a rough estimate of the limiting mass loss rateṀ lim that is required for a species with mass M c (in units of m H ) to escape with H owing to neutral-neutral collisionṡ…”

Section: (C) Escape Rates and Mixingmentioning

confidence: 99%

Thermal escape from extrasolar giant planets

Koskinen

Lavvas

Harris

et al. 2014

Phil. Trans. R. Soc. A.

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The detection of hot atomic hydrogen and heavy atoms and ions at high altitudes around close-in extrasolar giant planets (EGPs) such as HD209458b implies that these planets have hot and rapidly escaping atmospheres that extend to several planetary radii. These characteristics, however, cannot be generalized to all close-in EGPs. The thermal escape mechanism and mass loss rate from EGPs depend on a complex interplay between photochemistry and radiative transfer driven by the stellar UV radiation. In this study, we explore how these processes change under different levels of irradiation on giant planets with different characteristics. We confirm that there are two distinct regimes of thermal escape from EGPs, and that the transition between these regimes is relatively sharp. Our results have implications for thermal mass loss rates from different EGPs that we discuss in the context of currently known planets and the detectability of their upper atmospheres.

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Section: (C) Escape Rates and Mixingmentioning

confidence: 99%

Thermal escape from extrasolar giant planets

Koskinen

Lavvas

Harris

et al. 2014

Phil. Trans. R. Soc. A.

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“…What happened between the end of accretion and 4.4 Gyr ago is, of course, very uncertain. The planet was probably rapidly outgassing, and volatile elements were being removed by hydrodynamic escape [Hunten et al, 1987;Pepin, 1991Pepin, , 1994. The heat flow must have been rapidly declining [Schubert et al, 1992], and the mix of impacting objects must have been rapidly changing.…”

Section: Description Of the Modelmentioning

confidence: 99%

Retention of an atmosphere on early Mars

Carr¹

1999

J. Geophys. Res.

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Abstract. The presence of valley networks and indications of high erosion rates in ancient terrains on Mars suggest that Mars was warm and wet during heavy bombardment. Various processes that could occur on early Mars were integrated into a self-consistent model to determine what circumstances might lead to warm temperatures during and at the end of heavy bombardment. Included were weathering and burial of CO2 as carbonates, impact erosion, sputtering, and recycling of CO2 back into the atmosphere by burial and heating. The models suggest that despite losses from the atmosphere by weathering and impact erosion, Mars could retain a 0.5 to 1 bar atmosphere at the end of heavy bombardment partly because weathering temporarily sequesters CO2 in the ground and protects it from impact erosion while the impact rate is declining and impact erosion is becoming less effective. Because of the low output of the early Sun, surface temperatures can be above freezing only for a very efficient greenhouse, such as that suggested by Forget and Pierrehumbert [1997]. With weak greenhouse models, temperatures are below freezing throughout heavy bombardment, and such a large amount of CO2 is left in the atmosphere at the end of heavy bombardment that it is difficult to eliminate subsequently to arrive at the present surface inventory. With strong greenhouse models, temperatures are well above freezing during heavy bombardment and drop to close to freezing at the end of heavy bombardment, at which time the atmosphere contains 0.5 to 1 bar of CO2. This can be largely eliminated subsequently by sputtering and lowtemperature weathering. Such a model is consistent with the change in erosion rate and the declining rate of valley formation at the end of heavy bombardment. Conditions that favor warm temperatures at the end of heavy bombardment are an efficient greenhouse, low weathering rates, low impact erosion rates, and a smaller fraction of heat lost by conduction as opposed to transport of lava to the surface. IntroductionGeomorphic evidence of high erosion rates and liquid water on early Mars suggests that early Mars was warmer and wetter and had a thicker atmosphere than it had for most of its subsequent history. This paper explores various ways that a thick CO2-H20 atmosphere could have been sustained on early Mars despite the tendency of large impacts to erode it away and despite the tendency of weathering to convert CO2 to carbonates and sequester it in the ground.

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“…Thus, heavier particles are less entrained, and this is particularly true of isotopes of an element which have identical cross-sections but different masses. Hunten et al ( 1987) have derived the equations for mass fractionation of heavy gases in an isothermal, neutral atmosphere. The effect of hydrodynamic escape of hydrogen on noble gas abundances and isotopic compositions in planetary atmospheres has been given by Pepin ( 1991).…”

Section: Volatile Loss From > 100 Km Bodiesmentioning

confidence: 99%

“…This can be shown to be the case for noble gas loss from planetary atmospheres (Pepin,199 1 ), which involves the preferential depletion of light noble gases, e.g., He, Ne, and Ar, relative to Kr and Xe. There is, likewise, a large accompanying isotopic fractionation (Hunten et al, 1987 ) which may have enriched the 38Ar/36Ar ratio in the Martian atmosphere. The largest chemical effect on planetary compositions would be severe depletion of the Li/Yb ratio, which has been found to be relatively constant between various planetary reservoirs (Norman and Taylor, 1992).…”

Section: Chemical and Isotopic Consequences Of Atmospheric Lossmentioning

confidence: 99%