Mössbauer Study of Weathered H-meteorite from the Desert of Oman

A number of meteorites from the desert of Oman, classified as H-chondrites, with known and unknown ages, were studied by using 57Fe Mössbauer spectroscopy to determine their Fe3+-bearing compositions. Mössbauer spectra measured at 78 K were composed of paramagnetic doublets superimposed on magnetic sextets. The doublets are assigned to the silicate minerals olivine and pyroxene and Fe3+ phases. The magnetic sextets in most samples showed the presence of at least three magnetic phases, namely troilite, magnetite and kamacite, which commonly exist in most ordinary chondrites. The relative amounts (area %) of Fe3+ in the known-age meteorites, determined from the Mössbauer spectra, were plotted against their terrestrial ages. The plot was used to estimate the terrestrial ages of meteorites with unknown terrestrial age.

Maryborough, a new H5 meteorite find from Victoria, Australia

The Maryborough meteorite is a new H5 ordinary chondrite discovered about 2 km south of Maryborough, Victoria, in May 2015. It is a single stone measuring approximately 39 × 14 × 14 cm and with a mass of 17 kg. Plentiful indistinct chondrules are up to 1 mm across in a strongly recrystallised plagioclase-bearing matrix. Olivine and orthopyroxene in both the matrix and chondrules are uniform in composition (Fo80.1Fa19.3Te0.5Ca-ol0.04 and En81.5Fs17.1Wo1.5 respectively).The main metallic phases present are kamacite, taenite and tetrataenite, often forming composite grains with troilite. There is no evidence for any shock-inducing event and the meteorite shows incipient weathering in the form of thin iron-oxide mantles around the Fe–Ni grains. A terrestrial age of less than 1000 years is estimated from C14 dating. While there are a number of historic reported meteor sightings in the Maryborough district, none can be tied to the meteorite’s find site. To date, Maryborough is the third H5 ordinary chondrite and the second largest single chondritic mass, after Kulnine (55 kg), found in Victoria.

Current Performance and Preliminary Results of a New 14C Extraction Line for Meteorites at the University of Bern

Here, we introduce a new radiocarbon (14C) extraction line operating at the University of Bern, which was designed and built for the extraction of in situ 14C from meteorites. With this system, we achieved two important developments compared to other systems. First, using the MICADAS gas-interface system, 14C can directly be measured from the collected CO2 gas, i.e., without graphitization of the sample. Second, meteorite sample masses as low as ~0.05 g can be used for high precision and reproducibility. Prior to extraction in an oxygen atmosphere held at a pressure of ~20–30 mbar in an iridium crucible at 1600°C for 40 min, samples were preheated for 1 h in a constant oxygen flow at 500°C and continuous pumping. Gas purification followed the method described previously (e.g., Hippe et al. 2009). While the blank levels for preheated samples are low (<2×104 14C atoms), the blanks for non-preheated samples are high, therefore those results cannot be used. We also report preliminary results for the L-chondrite JaH 073. The terrestrial age of 17.7±0.4 ka is in good agreement with previous results for the same sample of this meteorite, confirming that the extraction line, the gas purification system, and the AMS measurements are all reliable.

Radionuclide Studies of Stony Meteorites from Hot Deserts

We summarize the use of radiocarbon produced by spallation in meteorites in space to determine their terrestrial age or residence time. This “age” gives us important information as it can be compared to the rates of weathering and infall of meteorites. The processes that affect the collection of meteorites in a given area can be related to the rates of infall of new meteorites, and the rate of removal by chemical weathering and physical erosion.

The thermoluminescence of meteorites: A brief 2010 perspective

Early work on meteorite thermoluminescence, influenced by pottery dating and dosimetry applications, demonstrated a relationship between natural thermoluminescence and (1) the orbital perihelion of a meteorite and (2) the terrestrial age (time since fall) of a meteorite. For 14 years natural TL measurements were routinely made on newly recovered Antarctic meteorites to help identify unusual thermal and radiation histories, and to sort them by terrestrial age and perihelion. Two examples of the value of such data are presented, an Antarctic meteorite that underwent a major orbit change prior to fall and the collection mechanics of meteorites at the Lewis Cliff collection site. A second major area of focus for meteorite TL, that has no non-meteorite heritage, is the use of their induced TL to provide an extraordinarily sensitive and quantitative means of exploring metamorphic intensity and palaeothermometry. While especially valuable for unequilibrated ordinary chondrites, these types of measurement have proved useful with virtually every major class of meteorite, asteroidal and planetary. The challenge now is to extend the technique to small particles, micrometeorites, interplanetary dust particles, and cometary particles.

Thermoluminescence as a technique for determining the nature and history of small solar system particles

The thermoluminescence phenomenon has been used for pottery dating and radiation dosimetry for sixty years and for forty years has been applied to the study of meteorites, being successful in quantifying metamorphic histories and providing new insights into terrestrial age and orbits. Here we review some of the fundamental properties of thermoluminescence with particular focus on the study of small extraterrestrial particles. We suggest that natural TL data can be used to identify the burial and release history of cometary particles and that induced TL measurements can provide in-sights into the mineralogy of particles (even when largely amorphous) and the metamorphic history of those particles. We illustrate the use of TL to study small particles by describing recent studies on micrometeorites and 10–100 μm fragments taken from the matrix of a meteorite Semarkona which is type 3.0 ordinary chondrite.