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Matthew P Golombek - One of the best experts on this subject based on the ideXlab platform.
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amazonian chemical weathering rate derived from Stony meteorite finds at meridiani planum on mars
Nature Communications, 2016Co-Authors: Christian Schröder, Matthew P Golombek, J W Ashley, Philip A. Bland, J. A. GrantAbstract:Spacecraft exploring Mars such as the Mars Exploration Rovers Spirit and Opportunity, as well as the Mars Science Laboratory or Curiosity rover, have accumulated evidence for wet and habitable conditions on early Mars more than 3 billion years ago. Current conditions, by contrast, are cold, extremely arid and seemingly inhospitable. To evaluate exactly how dry today’s environment is, it is important to understand the ongoing current weathering processes. Here we present chemical weathering rates determined for Mars. We use the oxidation of iron in Stony Meteorites investigated by the Mars Exploration Rover Opportunity at Meridiani Planum. Their maximum exposure age is constrained by the formation of Victoria crater and their minimum age by erosion of the Meteorites. The chemical weathering rates thus derived are ∼1 to 4 orders of magnitude slower than that of similar Meteorites found in Antarctica where the slowest rates are observed on Earth. Little is known about the impacts of Mars’ contemporary dryness on weathering processes. Here, using iron oxidation estimates from the Mars Rover Opportunity, the authors quantify chemical weathering rates for Mars, finding appreciably slower rates compared with the lowest values on Earth.
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Properties and distribution of paired candidate Stony Meteorites at Meridiani Planum, Mars
Journal of Geophysical Research, 2010Co-Authors: Christian Schröder, J W Ashley, Kenneth E. Herkenhoff, William H. Farrand, John E. Chappelow, Wei Wang, Larry R. Nittler, Iris Fleischer, Ralf Gellert, Matthew P GolombekAbstract:[1] The Mars Exploration Rover Opportunity investigated four rocks, informally dubbed Barberton, Santa Catarina, Santorini, and Kasos, that are possible Stony Meteorites. Their chemical and mineralogical composition is similar to the howardite, eucrite, and diogenite group but with additional metal, similar to mesosiderite silicate clasts. Because of their virtually identical composition and because they appear to represent a relatively rare group of Meteorites, they are probably paired. The four rocks were investigated serendipitously several kilometers apart, suggesting that Opportunity is driving across a larger population of similar rock fragments, maybe a meteorite strewn field. Small amounts of ferric Fe are a result of weathering. We did not observe evidence for fusion crusts. Four iron Meteorites were found across the same area. Although mesosiderites are Stony irons, a genetic link to these irons is unlikely. The Stony Meteorites probably fell later than the irons. The current atmosphere is sufficiently dense to land such Meteorites at shallow entry angles, and it would disperse fragments over several kilometers upon atmospheric breakup. Alternatively, dispersion by spallation from an impacting meteoroid may have occurred. Santa Catarina and a large accumulation of similar rocks were found at the rim of Victoria crater. It is possible that they are associated with the impactor that created Victoria crater, but our limited knowledge about their distribution cannot exclude mere coincidence.
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event and conditions that produced the iron meteorite block island on mars
Journal of Geophysical Research, 2010Co-Authors: John E. Chappelow, Matthew P GolombekAbstract:[1] The Mars Exploration Rover Opportunity has discovered four large iron-nickel Meteorites that range in size from 50 to 240 kg dispersed over 10 km of Meridiani Planum, Mars. Because these Meteorites are covered with hollows that resemble regmaglypts, their surfaces record their ablation through the atmosphere, and they must have landed at speeds below hypervelocity (<2 km s−1) to survive. Slowing massive iron Meteorites requires a minimum atmospheric density, which was quantified using a numerical model that integrates the equations of motion for incoming meteoroids through an atmosphere of a given surface density and scale height and records their outcomes as direct (generally hypervelocity impacts that form craters), longer over the horizon and fallback flight paths, and skip outs. The present atmosphere of Mars is sufficient to slow iron meteoroids as large as Block Island (the most massive meteorite) via drag and significant ablation on long flight paths, although for standard distributions of entering meteoroid masses, velocities, and entry angles, such events are rare (0.007% of incoming iron meteoroids). Such events require entry angles of 10°–13°, entry velocities of 6–18 km s−1, and entry masses of 225–710 kg. The absence of large Stony Meteorites is probably at least partially because they are much weaker and thus broken up into smaller fragments on impact. Although differential drag deceleration on long flight paths could disperse fragments of an entering meteoroid by tens of kilometers, dynamic pressures are too low to break up an iron meteorite, leaving the possibility that they are paired an open question.
Jozef Masarik - One of the best experts on this subject based on the ideXlab platform.
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Thermal neutron capture effects in radioactive and stable nuclide systems
Meteoritics & Planetary Science, 2013Co-Authors: Ingo Leya, Jozef MasarikAbstract:Neutron capture effects in Meteorites and lunar surface samples have been successfully used in the past to study exposure histories and shielding conditions. In recent years, however, it turned out that neutron capture effects produce a nuisance for some of the short-lived radionuclide systems. The most prominent example is the 182Hf-182W system in iron Meteorites, for which neutron capture effects lower the 182W/184W ratio, thereby producing too old apparent ages. Here, we present a thorough study of neutron capture effects in iron Meteorites, ordinary chondrites, and carbonaceous chondrites, whereas the focus is on iron Meteorites. We study in detail the effects responsible for neutron production, neutron transport, and neutron slowing down and find that neutron capture in all studied meteorite types is not, as usually expected, exclusively via thermal neutrons. In contrast, most of the neutron capture in iron Meteorites is in the epithermal energy range and there is a significant contribution from epithermal neutron capture even in Stony Meteorites. Using sophisticated particle spectra and evaluated cross section data files for neutron capture reactions we calculate the neutron capture effects for Sm, Gd, Cd, Pd, Pt, and Os isotopes, which all can serve as neutron-dose proxies, either in Stony or in iron Meteorites. In addition, we model neutron capture effects in W and Ag isotopes. For W isotopes, the GCR-induced shifts perfectly correlate with Os and Pt isotope shifts, which therefore can be used as neutron-dose proxies and permit a reliable correction. We also found that GCR-induced effects for the 107Pd-107Ag system can be significant and need to be corrected, a result that is in contrast to earlier studies.
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Cosmogenic nuclides in Stony Meteorites revisited
Meteoritics & Planetary Science, 2009Co-Authors: Ingo Leya, Jozef MasarikAbstract:We present new model calculations for depth and size dependent cosmogenic production rates in ordinary and carbonaceous chondrites by galactic cosmic rays. This model, essentially that of Leya et al. (2000a), folds together particle spectra and cross sections for the relevant nuclear reactions, but has been significantly improved due to major improvements in the neutron cross section database and better Monte Carlo modeling of the primary and the secondary particle spectra. The data presented here replace (and extend) the results of our earlier model predictions. Here we give for ordinary and carbonaceous chondrites elemental production rates for the cosmogenic radionuclides 10Be, 14C, 26Al, 36Cl, 41Ca, 53Mn, 60Fe, and 129I as well as for the noble gas isotopes 3He, 4He, 20Ne, 21Ne, 22Ne, 36Ar, and 38Ar. Using the new data and expressing size and depth scales to the unit [g/cm2], we are able to demonstrate that the matrix effect for both chondrite types is negligible for all target product combinations, except for those which are dominated by thermal or very low energy neutron reactions. Based on the new model predictions, we present a variety of elemental and isotopic production rate ratios allowing for a reliable determination of preatmospheric sizes, shielding depths, cosmic-ray exposure ages, and diffusive losses.
Ingo Leya - One of the best experts on this subject based on the ideXlab platform.
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Thermal neutron capture effects in radioactive and stable nuclide systems
Meteoritics & Planetary Science, 2013Co-Authors: Ingo Leya, Jozef MasarikAbstract:Neutron capture effects in Meteorites and lunar surface samples have been successfully used in the past to study exposure histories and shielding conditions. In recent years, however, it turned out that neutron capture effects produce a nuisance for some of the short-lived radionuclide systems. The most prominent example is the 182Hf-182W system in iron Meteorites, for which neutron capture effects lower the 182W/184W ratio, thereby producing too old apparent ages. Here, we present a thorough study of neutron capture effects in iron Meteorites, ordinary chondrites, and carbonaceous chondrites, whereas the focus is on iron Meteorites. We study in detail the effects responsible for neutron production, neutron transport, and neutron slowing down and find that neutron capture in all studied meteorite types is not, as usually expected, exclusively via thermal neutrons. In contrast, most of the neutron capture in iron Meteorites is in the epithermal energy range and there is a significant contribution from epithermal neutron capture even in Stony Meteorites. Using sophisticated particle spectra and evaluated cross section data files for neutron capture reactions we calculate the neutron capture effects for Sm, Gd, Cd, Pd, Pt, and Os isotopes, which all can serve as neutron-dose proxies, either in Stony or in iron Meteorites. In addition, we model neutron capture effects in W and Ag isotopes. For W isotopes, the GCR-induced shifts perfectly correlate with Os and Pt isotope shifts, which therefore can be used as neutron-dose proxies and permit a reliable correction. We also found that GCR-induced effects for the 107Pd-107Ag system can be significant and need to be corrected, a result that is in contrast to earlier studies.
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Cosmogenic nuclides in Stony Meteorites revisited
Meteoritics & Planetary Science, 2009Co-Authors: Ingo Leya, Jozef MasarikAbstract:We present new model calculations for depth and size dependent cosmogenic production rates in ordinary and carbonaceous chondrites by galactic cosmic rays. This model, essentially that of Leya et al. (2000a), folds together particle spectra and cross sections for the relevant nuclear reactions, but has been significantly improved due to major improvements in the neutron cross section database and better Monte Carlo modeling of the primary and the secondary particle spectra. The data presented here replace (and extend) the results of our earlier model predictions. Here we give for ordinary and carbonaceous chondrites elemental production rates for the cosmogenic radionuclides 10Be, 14C, 26Al, 36Cl, 41Ca, 53Mn, 60Fe, and 129I as well as for the noble gas isotopes 3He, 4He, 20Ne, 21Ne, 22Ne, 36Ar, and 38Ar. Using the new data and expressing size and depth scales to the unit [g/cm2], we are able to demonstrate that the matrix effect for both chondrite types is negligible for all target product combinations, except for those which are dominated by thermal or very low energy neutron reactions. Based on the new model predictions, we present a variety of elemental and isotopic production rate ratios allowing for a reliable determination of preatmospheric sizes, shielding depths, cosmic-ray exposure ages, and diffusive losses.
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cosmic ray production of tungsten isotopes in lunar samples and Meteorites and its implications for hf w cosmochemistry
Earth and Planetary Science Letters, 2000Co-Authors: Ingo Leya, R Wieler, Alex N HallidayAbstract:Excesses and deficiencies in 182W in Meteorites and lunar samples relative to the terrestrial 182W atomic abundance have been assigned to the decay of 182Hf (t1/2=9 Ma) and have been used to date metal-silicate fractionation events in the early solar system. Because the effects are very small, production and burn-out of tungsten isotopes by cosmic ray interactions are a concern in such studies. Masarik [J. Masarik, Contribution of neutron-capture reactions to observed tungsten isotopic ratios, Earth Planet. Sci. Lett. 152 (1997) 181–185] showed that neutron-capture reactions on tungsten isotopes can account at best for a minor part of the observed deficit of 182W in Toluca and other iron Meteorites. On the other hand, in lunar samples and Stony Meteorites the production of 182W from 181Ta may become crucial. Here, we calculate this contribution as well as production and consumption of 182–186W by other neutron-induced reactions. The neutron fluence of each sample is estimated by its nominal cosmic-ray exposure age deduced from noble gas data. This approach overestimates the true cosmogenic W isotopic shifts for samples that might have been irradiated very close to the regolith surface. A quantitative estimate is often also hampered by a lack of Ta data. Despite these reservations, it appears that in many lunar samples neutron-capture on Ta has caused a large part of the observed 182W excess. On the other hand, in some samples, especially those with very low exposure ages, clearly only a minor or even negligible fraction of the 182W excess can be cosmogenic. Therefore, the conclusion, based on Hf–W model ages, that the Moon formed 50 Myr after the start of the solar system remains valid. Martian Meteorites have lower Ta/W ratios and cosmic ray exposure ages than most lunar samples. Therefore, cosmogenic production has not significantly altered the W isotopic composition in Martian Meteorites. Observed 182W excesses in Martian Meteorites as well as the very large excesses in two eucrites are undoubtedly the result of early 182Hf decay.
Christian Schröder - One of the best experts on this subject based on the ideXlab platform.
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amazonian chemical weathering rate derived from Stony meteorite finds at meridiani planum on mars
Nature Communications, 2016Co-Authors: Christian Schröder, Matthew P Golombek, J W Ashley, Philip A. Bland, J. A. GrantAbstract:Spacecraft exploring Mars such as the Mars Exploration Rovers Spirit and Opportunity, as well as the Mars Science Laboratory or Curiosity rover, have accumulated evidence for wet and habitable conditions on early Mars more than 3 billion years ago. Current conditions, by contrast, are cold, extremely arid and seemingly inhospitable. To evaluate exactly how dry today’s environment is, it is important to understand the ongoing current weathering processes. Here we present chemical weathering rates determined for Mars. We use the oxidation of iron in Stony Meteorites investigated by the Mars Exploration Rover Opportunity at Meridiani Planum. Their maximum exposure age is constrained by the formation of Victoria crater and their minimum age by erosion of the Meteorites. The chemical weathering rates thus derived are ∼1 to 4 orders of magnitude slower than that of similar Meteorites found in Antarctica where the slowest rates are observed on Earth. Little is known about the impacts of Mars’ contemporary dryness on weathering processes. Here, using iron oxidation estimates from the Mars Rover Opportunity, the authors quantify chemical weathering rates for Mars, finding appreciably slower rates compared with the lowest values on Earth.
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Properties and distribution of paired candidate Stony Meteorites at Meridiani Planum, Mars
Journal of Geophysical Research, 2010Co-Authors: Christian Schröder, J W Ashley, Kenneth E. Herkenhoff, William H. Farrand, John E. Chappelow, Wei Wang, Larry R. Nittler, Iris Fleischer, Ralf Gellert, Matthew P GolombekAbstract:[1] The Mars Exploration Rover Opportunity investigated four rocks, informally dubbed Barberton, Santa Catarina, Santorini, and Kasos, that are possible Stony Meteorites. Their chemical and mineralogical composition is similar to the howardite, eucrite, and diogenite group but with additional metal, similar to mesosiderite silicate clasts. Because of their virtually identical composition and because they appear to represent a relatively rare group of Meteorites, they are probably paired. The four rocks were investigated serendipitously several kilometers apart, suggesting that Opportunity is driving across a larger population of similar rock fragments, maybe a meteorite strewn field. Small amounts of ferric Fe are a result of weathering. We did not observe evidence for fusion crusts. Four iron Meteorites were found across the same area. Although mesosiderites are Stony irons, a genetic link to these irons is unlikely. The Stony Meteorites probably fell later than the irons. The current atmosphere is sufficiently dense to land such Meteorites at shallow entry angles, and it would disperse fragments over several kilometers upon atmospheric breakup. Alternatively, dispersion by spallation from an impacting meteoroid may have occurred. Santa Catarina and a large accumulation of similar rocks were found at the rim of Victoria crater. It is possible that they are associated with the impactor that created Victoria crater, but our limited knowledge about their distribution cannot exclude mere coincidence.
J. A. Grant - One of the best experts on this subject based on the ideXlab platform.
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amazonian chemical weathering rate derived from Stony meteorite finds at meridiani planum on mars
Nature Communications, 2016Co-Authors: Christian Schröder, Matthew P Golombek, J W Ashley, Philip A. Bland, J. A. GrantAbstract:Spacecraft exploring Mars such as the Mars Exploration Rovers Spirit and Opportunity, as well as the Mars Science Laboratory or Curiosity rover, have accumulated evidence for wet and habitable conditions on early Mars more than 3 billion years ago. Current conditions, by contrast, are cold, extremely arid and seemingly inhospitable. To evaluate exactly how dry today’s environment is, it is important to understand the ongoing current weathering processes. Here we present chemical weathering rates determined for Mars. We use the oxidation of iron in Stony Meteorites investigated by the Mars Exploration Rover Opportunity at Meridiani Planum. Their maximum exposure age is constrained by the formation of Victoria crater and their minimum age by erosion of the Meteorites. The chemical weathering rates thus derived are ∼1 to 4 orders of magnitude slower than that of similar Meteorites found in Antarctica where the slowest rates are observed on Earth. Little is known about the impacts of Mars’ contemporary dryness on weathering processes. Here, using iron oxidation estimates from the Mars Rover Opportunity, the authors quantify chemical weathering rates for Mars, finding appreciably slower rates compared with the lowest values on Earth.