The dating of pre-exposure times of lunar rocks and soils

Xenon produced by fission of uranium, thorium and plutonium has repeatedly been observed in lunar rocks and soils. In two basaltic rocks and in two soils Xe was found originating from fission of U-235 induced by neutrons which are due to the interactions of cosmic ray particles with lunar matter. Two facts lead to this conclusion: (1) fission Xe is present in excess of that expected for the U, Th, and Pu concentrations and for the gas retention age of the samples; and (2) the Xe-134/Xe-136 ratio of excess fission Xe is close to 1.25 as expected for neutron induced fission of U-235. Information on the duration of the exposure to cosmic rays was obtained from the Kr-81-Kr systematics whereas the effective shielding conditions were derived from the depth sensitive cosmogenic ratio Xe-131/Xe-126. For the four samples the exposure to cosmic rays in the lunar regolith is described by a two stage exposure model. The history of the four samples was derived in terms of duration and shielding depth of the two stages

The composition of lunar noble gases traped 2.5 AE and 3.5 AE ago

The times when the soils 74001 and 73261 were exposed on the lunar surface were determined by the U-235 - Xe-136 dating method. The isotopic composition of the trapped noble gases in these two soils is compared with that of the surface correlated noble gases in the young soils 12001 and in the present day solar wind. The surface correlated trapped gases are a mixture of implanted solar wind particles and retrapped lunar atmospheric gases. The observed changes are interpreted as a result of decreasing outgassing of radiogenic Ar-40 and perhaps He-4 and of fissiogenic Xe from the lunar crust. The old soils probably also contain surface correlated Kr-80 and Kr-82 produced by secondary cosmic ray neutron capture of adsorbed or retrapped bromine. To some extent the isotopic composition of the trapped gases in old lunar soil may also have been altered due to diffusion loss from material of low retentivity

Plutonium-Xenon systematics of Angrites

Introduction: Angrites are igneous meteorites that crystallized very early in the solar system, ~10 Ma after CAIs, as also implied by the presence of now extinct short-lived radionuclides such as 53Mn, 146Sm and 244Pu [1]. Fission Xe was used to calculate 244Pu-136Xeretention ages of eucrites, relative to that of Angra dos Reis (AdoR) [2]. AdoR has an absolute Pb-Pb age of 4557.8 Ma [see 1 for ref.]. Most eucrites, being as old as angrites, experienced various parent body processes leading to ages ranging from ~20 Ma before, to ~100 Ma after AdoR [2]. Angrites, however, remained largely unaltered after differentiation. Here, we examine whether Xe isotopic characteristics allow determining an age sequence for angrites

The trapped heavy noble gases in recently found Martian meteorites

The composition of the trapped Ar, Kr, and Xe in the Martian meteorites Los Angeles, Say Al Uhaymir 005/008, and 094 is discussed and found to be consistent with a mixture of Martian mantle and atmosphere noble gases and terrestrial contamination

The pre-atmospheric size of Martian meteorites

The pre-atmospheric size of martian meteorites was calculated based on 80Kr produced by epithermal secondary cosmic-ray produced neutrons of 30-300 eV energy. For seven meteorites we obtained minimum radii of 22-27 cm, corresponding to 150-270 kg

Solar noble gases in the Angrite parent body – Evidence from volcanic volatiles trapped in D'Orbigny glass

We compare the noble gases in D'Orbigny glass and bulk. The glass was formed after the bulk silicates and contains interior solar noble gases that may originate from early volcanic activity on the angrite parent body, trapped upon fast cooling

Exposure age and terrestrial age of the paired meteorites Yamato-82192 and -82193 from the moon

The isotopic abundances of the noble gases in the lunar meteorites Yamato-82192 and -82193 were investigated with emphasis on the determination of the exposure history and the terrestrial age. Both meteorites contain low amounts of solar wind trapped noble gases indicating that the breccia grains resided for a very brief period of time on the lunar surface compared to typical lunar soil. Strong gas losses are reflected by the extremely low concentrations of He. Identical exposure histories are derived for both meteorites confirming earlier suggestions that they represent a paired fall. The investigated samples experienced a shallow shielding to cosmic rays of less than 25g/cm^2. From the activity of cosmogenic radionuclides we conclude that the meteoroid spent at least 5Ma of its most recent exposure history in free space. Assuming excavation on the Moon from a depth completely shielded from cosmic rays and propulsion into Earth orbit by the same impact event we calculate a Moon-Earth transit time, i. e. an exposure age in free space at 4π exposure geometry of 11±2Ma. The terrestrial age of the Y-82192/3 meteorite is 70000 to 80000 years which is typical for the meteorites collected in the Yamato Mountains

Element distribution and noble gas isotopic abundances in lunar meteorite Allan Hills A81005

Antarctic meteorite ALLAN HILLS A81005, an anorthositic breccia, is recognized to be of lunar origin. The noble gases in this meteorite were analyzed and found to be solar-wind implanted gases, whose absolute and relative concentrations are quite similar to those in lunar regolith samples. A sample of this meteorite was obtained for the analysis of the noble gas isotopes, including Kr(81), and for the determination of the elemental abundances. In order to better determine the volume derived from the surface correlated gases, grain size fractions were prepared. The results of the instrumental measurements of the gamma radiation are listed. From the amounts of cosmic ray produced noble gases and respective production rates, the lunar surface residence times were calculated. It was concluded that the lunar surface time is about half a billion years

The ingredients of the “Subsolar” noble gas component

On the basis of several experiments on separates of the EH5 chondrite St. Mark–s, we will argue that the 'subsolar' noble gas component is a mixture of solar-like, Q- and terrestrial noble gases

The interstellar gas experiment

The Interstellar Gas Experiment (IGE) exposed thin metallic foils to collect neutral interstellar gas particles. These particles penetrate the solar system due to their motion relative to the sun. Thus, it is possible to entrap them in the collecting foils along with precipitating magnetospheric and perhaps some ambient atmospheric particles. For the entire duration of the Long Duration Exposure Facility (LDEF) mission, seven of these foils collected particles arriving from seven different directions as seen from the spacecraft. In the mass spectroscopic analysis of the noble gas component of these particles, we have detected the isotopes of He-3, He-4, Ne-20, and Ne-22. In the foil analyses carried out so far, we find a distribution of particle arrival directions which shows that a significant part of the trapped particles are indeed interstellar atoms. The analysis needed to subtract the competing fluxes of magnetospheric and atmospheric particles is still in progress