The density and porosity of lunar rocks

Accurate lunar rock densities are necessary for constructing gravity models of the Moon\u27s crust and lithosphere. Most Apollo-era density measurements have errors of 2-5% or more and few include porosity measurements. We report new density and porosity measurements using the bead method and helium pycnometry for 6 Apollo samples and 7 lunar meteorites, with typical grain density uncertainties of 10-30 kg m(-3) (0.3-0.9%) and porosity uncertainties of 1-3%. Comparison between igneous grain densities and normative mineral densities show that these uncertainties are realistic and that the helium fully penetrates the pore space. Basalt grain densities are a strong function of composition, varying over at least 3270 kg m(-3) (high aluminum basalt) to 3460 kg m(-3) (high titanium basalt). Feldspathic highland crust has a bulk density of 22002600 kg m(-3) and porosity of 10-20%. Impact basin ejecta has a bulk density of 2350-2600 kg m(-3) and porosity of similar to 20%

Heterogeneity in lunar anorthosite meteorites: Implications for the lunar magma ocean model

The lunar magma ocean model is a well-established theory of the early evolution of the Moon. By this model, the Moon was initially largely molten and the anorthositic crust that now covers much of the lunar surface directly crystallized from this enormous magma source. We are undertaking a study of the geochemical characteristics of anorthosites from lunar meteorites to test this model. Rare earth and other element abundances have been measured in situ in relict anorthosite clasts from two feldspathic lunar meteorites: Dhofar 908 and Dhofar 081. The rare earth elements were present in abundances of approximately 0.1 to approximately 10× chondritic (CI) abundance. Every plagioclase exhibited a positive Eu-anomaly, with Eu abundances of up to approximately 20×CI. Calculations of the melt in equilibrium with anorthite show that it apparently crystallized from a magma that was unfractionated with respect to rare earth elements and ranged in abundance from 8 to 80×CI. Comparisons of our data with other lunar meteorites and Apollo samples suggest that there is notable heterogeneity in the trace element abundances of lunar anorthosites, suggesting these samples did not all crystallize from a common magma source. Compositional and isotopic data from other authors also suggest that lunar anorthosites are chemically heterogeneous and have a wide range of ages. These observations may support other models of crust formation on the Moon or suggest that there are complexities in the lunar magma ocean scenario to allow for multiple generations of anorthosite formation

Meteoritical Evidence And Constraints On Asteroid Impacts And Disruption

Impact events have played a central role in the life of meteorites. They compacted and lithified the dust from which meteorites are made; produced shock minerals, shock melting, and shock blackening of meteoritic minerals on their parent bodies; turned their parent bodies into rubble; and dispersed at least some pieces of this rubble, sending them to Earth as meteorites. Thus, as well as owing their very existence to the occurrence of catastrophic disruptions, meteorites contain physical ground truth concerning the impact and disruption environment of the solar system. Reviewing these aspects of the impact-meteorite connection, we conclude that impacts severe enough to disrupt asteroids were rare in the earliest stages of the solar nebula, when meteorite parent bodies accreted and were lithified. Likewise, though catastrophic disruptions clearly have occurred over the past several billion years, the small number of exposure events seen in the meteoritic cosmic ray age record indicates that such disruptions at these times also were rare. However, catastrophic disruptions must have been very prevalent during the first billion years of the solar system, resulting in the widespread asteroid macroporosity inferred from the comparison of asteroid bulk densities to meteorite grain densities. © 2004 Elsevier Ltd. All rights reserved

Density, Porosity, And Magnetic Susceptibility Of Carbonaceous Chondrites

We report physical properties (bulk and grain density, magnetic susceptibility, and porosity) measured using nondestructive and noncontaminating methods for 195 stones from 63 carbonaceous chondrites. Grain densities over the whole population average 3.44gcm-3, ranging from 2.42gcm-3 (CI1 Orgueil) to 5.66gcm-3 (CB Bencubbin). Magnetic susceptibilities (in log units of 10-9m3kg-1) averaged logχ=4.22, ranging from 3.23 (CV3 Axtell) to 5.79 (CB Bencubbin). Porosities averaged 17%, ranging from 0 (for a number of meteorites) to 41% (for one stone of the CO Ornans). Notably, we found significant differences in porosity between the oxidized and reduced CV subgroups, with the porosities of CVo averaging approximately 20% and CVr porosities approximately 4%. Overall, porosities of carbonaceous chondrite falls trend with petrographic type, from type 1 (CI) near 35%, type 2 (CM, CR) averaging 23%, type 3 (CV, CO) 21%, to type 4 (CK and some CO) averaging 15%. There is also a significant decrease in porosity between meteorites of shock stage S1 and those of S2, indicative of shock compression. © The Meteoritical Society, 2011

Density, Porosity, And Magnetic Susceptibility Of Achondritic Meteorites

+Abstract-: As part of a large-scale survey of meteorite bulk and grain densities, porosities, and magnetic susceptibilities, we measured these properties for 174 stones from 106 achondritic meteorites. These include four lunar meteorites, 15 stones from 10 shergottites, nakhlites, and chassignites (SNCs), 96 stones from 56 howardites, eucrites, and diogenites (HEDs), 17 stones from nine aubrites, two angrites, and 16 stones from 10 ureilites, four stones of three acapulcoites, as well as four stones of three lodranites, and 15 stones from eight primitive achondrites. Those meteorites derived from basalts and crustal material of differentiated parent bodies have lower densities and magnetic susceptibilities, on an average, than the more primitive achondrites, which have a higher percentage metal. A notable exception is the one chassignite in the study (Chassigny), which has a high grain density of 3.73±0.04gcm-3. Ureilites have magnetic susceptibilities consistent with primitive achondrites, but lower grain densities. Porosities do not vary considerably between most of the groups, with most stones 5-14% porous, although on an average, ureilites and brachinites have lower porosities, with most stones less than 7% porous. For primitive achondrites, the higher metal content causes finds to exhibit weathering effects similar to what is observed in ordinary chondrites, with a reduction in grain density, magnetic susceptibility, and porosity as compared with unweathered falls. For lunites, SNCs, and HEDs, no such effect is observed. We also observe that grain density and magnetic susceptibility used in conjunction distinguish shergottites, nakhlites, and chassignites from each other. Shergottites and nakhlites have low grain densities (averaging 3.31 and 3.41gcm-3, respectively) whereas Chassigny is 3.7gcm-3. In magnetic susceptibility, shergottities and chassignites are similar (averaging 2.85 and 2.98 in log units of 10-9m3kg-1, respectively) with nakhlites averaging higher at 3.42. © The Meteoritical Society, 2011

Enstatite Chondrite Density, Magnetic Susceptibility, And Porosity

As part of our continuing survey of meteorite physical properties, we measured grain and bulk density, porosity, and magnetic susceptibility for 41 stones from 23 enstatite chondrites (ECs), all with masses greater than 10-g, representing the majority of falls and a significant percentage of all available non-Antarctic EC meteorites. Our sampling included a mix of falls and finds. For falls, grain densities range from 3.45 to 4.17-g-cm-3, averaging 3.66-g-cm-3; bulk densities range from 3.15 to 4.10-g-cm-3, averaging 3.55-g-cm-3; porosities range from 0 to 12% with the majority less than 7%, and magnetic susceptibilities (in log units of 10-9-m3-kg-1) from 5.30 to 5.64, with an average of 5.47. For finds, weathering reduces both grain and bulk densities as well as magnetic susceptibilities. On average, finds have much higher porosity than falls. The two EC subgroups EH and EL, nominally distinguished by total iron content, exhibit similar values for all of the properties measured, indicating similar metallic iron content in the bulk stones of both subgroups. We also observed considerable intra-meteorite variation, with inhomogeneities in bulk and grain densities at scales up to approximately 40-g (approximately 12-cm3). © The Meteoritical Society, 2010

The Measurement Of Meteorite Heat Capacity At Low Temperatures Using Liquid Nitrogen Vaporization

Meteorite heat capacity (specific heat) is an essential parameter in modeling many aspects of the orbital and internal evolution of small solar system bodies, and can be a tool for characterization of the material in a meteorite itself. We have devised a novel method for the measurement of this quantity in whole- rock samples of meteorites, at low temperatures typical of asteroids. We insert the sample in liquid nitrogen, measure the mass of nitrogen boiled off due to the heat within the sample, and calibrating against measurements of pure quartz with a temperature-averaged heat capacity of 494J/kgK we calculate the temperature-average heat capacity of the sample. We show that this method is accurate, rapid, inexpensive, and non-destructive. Preliminary results for chondrites and metal rich meteorites are in excellent agreement with the literature data for meteorites, and hold the promise that such measurements may not only produce values useful to modelers but they also may provide an efficient way to classify whole meteorite samples and characterize subtle differences between meteorites of different compositional classes. © 2013 Elsevier Ltd

Magnetic classification of stony meteorites: 3. Achondrites

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The measurement of meteorite heat capacity at low temperatures using liquid nitrogen vaporization

Meteorite heat capacity (specific heat) is an essential parameter in modeling many aspects of the orbital and internal evolution of small solar system bodies, and can be a tool for characterization of the material in a meteorite itself. We have devised a novel method for the measurement of this quantity in whole- rock samples of meteorites, at low temperatures typical of asteroids. We insert the sample in liquid nitrogen, measure the mass of nitrogen boiled off due to the heat within the sample, and calibrating against measurements of pure quartz with a temperature-averaged heat capacity of 494J/kgK we calculate the temperature-average heat capacity of the sample. We show that this method is accurate, rapid, inexpensive, and non-destructive. Preliminary results for chondrites and metal rich meteorites are in excellent agreement with the literature data for meteorites, and hold the promise that such measurements may not only produce values useful to modelers but they also may provide an efficient way to classify whole meteorite samples and characterize subtle differences between meteorites of different compositional classes. © 2013 Elsevier Ltd

The measurement of meteorite heat capacity at low temperatures using liquid nitrogen vaporization

Meteorite heat capacity (specific heat) is an essential parameter in modeling many aspects of the orbital and internal evolution of small solar system bodies, and can be a tool for characterization of the material in a meteorite itself. We have devised a novel method for the measurement of this quantity in whole- rock samples of meteorites, at low temperatures typical of asteroids. We insert the sample in liquid nitrogen, measure the mass of nitrogen boiled off due to the heat within the sample, and calibrating against measurements of pure quartz with a temperature-averaged heat capacity of 494J/kgK we calculate the temperature-average heat capacity of the sample. We show that this method is accurate, rapid, inexpensive, and non-destructive. Preliminary results for chondrites and metal rich meteorites are in excellent agreement with the literature data for meteorites, and hold the promise that such measurements may not only produce values useful to modelers but they also may provide an efficient way to classify whole meteorite samples and characterize subtle differences between meteorites of different compositional classes. © 2013 Elsevier Ltd