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Xenon Fractionation and Archean Hydrogen EscapeXenon is the heaviest gas found in significant quantities in natural planetary atmospheres. It would seem the least likely to escape. Yet there is more evidence for xenon escape from Earth than for any element other than helium and perhaps neon. The most straightforward evidence is that most of the radiogenic Xe from the decay of (129)I (half-life 15.7 Myr) and (244)Pu (half-life 81 Myr) that is Earth's birthright is missing. The missing xenon is often attributed to the impact erosion of early atmospheres of Earth and its ancestors. It is obvious that if most of the radiogenic xenon were driven off by impacts, most of the rest of the atmophiles fared the same fate. The other line of evidence is in the nonradiogenic isotopes of xenon and its silent partner, krypton. Atmospheric xenon is strongly mass fractionated (at about 4% per amu) compared to any known solar system source (Figure 1). This is in stark contrast to krypton, which may not be fractionated at all: atmospheric Kr is slightly heavier than solar Kr (at about 0.5% per amu), but it is the same as in carbonaceous chondrites. Nonradiogenic xenon is also under abundant relative to krypton (the so-called "missing xenon" problem). Together these observations imply that xenon has been subject to fractionating escape and krypton not.
Document ID
20150010209
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Zahnle, K. J. (NASA Ames Research Center Moffett Field, CA United States)
Date Acquired
June 9, 2015
Publication Date
March 16, 2015
Subject Category
Astronomy
Report/Patent Number
ARC-E-DAA-TN20427
Meeting Information
Meeting: Lunar & Planetary Science Conference (LPSC)
Location: The Woodlands, TX
Country: United States
Start Date: March 16, 2015
End Date: March 20, 2015
Sponsors: Lunar and Planetary Inst., Universities Space Research Association
Funding Number(s)
WBS: WBS 811073.02.04.03.75
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
Keywords
magnetic fields
Xenon
planetary atmosphere

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