Meteoritics & Planetary Science, Volume 38, Number 7 (2003)
ABOUT THIS COLLECTION
Meteoritics & Planetary Science is an international monthly journal of the Meteoritical Society—a scholarly organization promoting research and education in planetary science. Topics include the origin and history of the solar system, planets and natural satellites, interplanetary dust and interstellar medium, lunar samples, meteors and meteorites, asteroids, comets, craters, and tektites.
Meteoritics & Planetary Science was first published in 1935 under the title Contributions of the Society for Research on Meteorites. In 1947, the publication became known as Contributions of the Meteoritical Society and continued through 1951. From 1953 to 1995, the publication was known as Meteoritics, and in 1996, the journal's name was changed to Meteoritics & Planetary Science or MAPS. The journal was not published in 1952 and from 1957 to 1964.
This archive provides access to Meteoritics & Planetary Science Volumes 37-44 (2002-2009).
Visit Wiley Online Library for new and retrospective Meteoritics & Planetary Science content (1935-present).ISSN: 1086-9379
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Recent Submissions
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Spectral properties and geologic processes on Eros from combined NEAR NIS and MSI data setsFrom April 24 to May 14, 2000, the Near Earth Asteroid Rendezvous (NEAR) Shoemaker mission's near infrared spectrometer (NIS) obtained its highest resolution data of 433 Eros. High signal-to-noise ratio NIS reflectance spectra cover a wavelength range of 800-2400 nm, with footprint sizes from 213 x 427 m to 394 x 788 m. This paper describes improvement in instrument calibration by remediation of internally scattered light; derivation of a "pseudo channel" for NIS at 754 nm using Multispectral Imager (MSI) Eros approach maps at 951 and 754 nm; synthesis of a 3127-spectrum high-resolution data set with the improved calibration and expanded wavelength coverage; and investigation of global and localized spectral variation with respect to mineralogy, composition, and space weathering of Eros, comparing the findings with previous analyses. Scattered light removal reduces the "red" slope of Eros spectra, though not to the level seen by telescopic observations. The pseudo channel completes sampling of Eros' 1 micron (Band I) absorption feature, enabling direct comparison of NIS data with other asteroid and meteorite spectra without additional scaling or correction. Following scattered light removal and wavelength range extension, the spectral parameters of average Eros plot well inside the S(IV) field of Gaffey et al. (1993) and are consistent with the L6 chondrite meteorite fields of Gaffey and Gilbert (1998). Although Eros shows no evidence of mineralogical heterogeneity, modest spectral variations correlate with morphologically and geographically distinct areas of the asteroid. Eros bright-to-dark spectral ratios are largely consistent with laboratory "space weathering" experiment results and modeling of space weathering effects. Eros brightness variation unaccompanied by significant spectral variation departs from "lunar-type"--where band depths, slopes, and albedoes all correlate--and "Ida-type"--where significant spectral variation is unaccompanied by corresponding brightness variation. The brightest areas on Eros--steep crater walls--have lesser spectral slope and deeper Band I, consistent with exposure of "fresher," less space weathered materials. Bright crater slope materials have opx/(opx + olv) of 0.24-0.29 and may be more representative of the subsurface mineralogy than "average" Eros, which is probably affected by space weathering. The floors of the large craters Psyche and Himeros have lower albedo and contain the most degraded or altered looking materials. NIS spectra retain a "red" spectral slope at greater than 2 microns. The recalibrated and expanded NIS spectra show better agreements with mixing models based on space weathering of chondritic mixtures.
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Woodleigh impact structure, Australia: Shock petrography and geochemical studiesThe large, complex Woodleigh structure in the Carnarvon basin of Western Australia has recently been added to the terrestrial impact crater record. Many aspects of this structure are, however, still uncertain. This work provides a detailed petrographic assessment of a suite of representative drill core samples from the borehole Woodleigh 1 that penetrated uplifted basement rocks of the central part of this structure. Fundamental rock and mineral deformation data and high-precision chemical data, including results of PGE and oxygen isotopic analysis, are presented. The sampled interval displays likely impact-produced macrodeformation in the form of fracturing and breccia veining at the microscopic scale. Contrary to earlier reports that these breccias represent pseudotachylite (friction melt) or even shock/shear-produced pseudotachylitic melt breccia cannot be confirmed due to pervasive post-impact alteration. Abundant planar deformation features (PDFs) in quartz, in addition to diaplectic glass and partial isotropization, are the main shock deformation effects observed, confirming that Woodleigh is of impact origin. Over the investigated depth interval, the statistics of quartz grains with a variable number of sets of PDFs does not change significantly, and the patterns of crystallographic orientations of PDFs in randomly selected quartz grains does not indicate a change in absolute shock pressure with depth either. The value of oxygen isotopes for the recognition of meteoritic contamination, as proposed by earlier Woodleigh workers, is critically assessed. Neither INA nor PGE analyses of our samples support the presence of a meteoritic component within this basement section, as had been claimed in earlier work.
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Impact tectonics in the core of the Vredefort dome, South Africa: Implications for central uplift formation in very large impact structuresThe 80 km wide Vredefort dome presents a unique opportunity to investigate the deep levels of the central uplift of a very large impact structure. Exposure of progressively older strata in the collar of the dome and of progressively higher-grade metamorphic rocks toward its center is consistent with differential uplift; however, the deepest levels exposed correspond to pre-impact mid- crust, rather than lower crust, as has been suggested previously. Pre-impact Archean gneissic fabrics in the core of the dome are differentially rotated, with the angle of rotation increasing sharply at a distance of ~16-19 km from the center. The present asymmetric dips of the collar strata, with layering dipping outward at moderate angles in the southeastern sector but being overturned and dipping inward in the northwestern sector, and the eccentric distribution of the pre-impact metamorphic isograds around the core of the dome can be reconciled with symmetric rotation of an initially obliquely NW-dipping target sequence during central uplift formation. The rocks in the core of the dome lack distinctive megablocks or large-slip-magnitude faults such as have been described in other central uplifts. We suggest that the large-scale coherent response of these rocks to the central uplift formation could have been accommodated by small-scale shear and/or rotation along pervasive pseudotachylitic breccia vein-fractures.
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Geochemical variability of the Yucatán basement: Constraints from crystalline clasts in Chicxulub impactitesThe 65 Ma old Chicxulub impact structure with a diameter of about 180 km is again in the focus of the geosciences because of the recently commenced drilling of the scientific well Yaxcopoil- 1. Chicxulub is buried beneath thick post-impact sediments, yet samples of basement lithologies in the drill cores provide a unique insight into age and composition of the crust beneath Yucatán. This study presents major element, Sr, and Nd isotope data for Chicxulub impact melt lithologies and clasts of basement lithologies in impact breccias from the PEMEX drill cores C-1 and Y-6, as well as data for ejecta material from the K/T boundaries at La Lajilla, Mexico, and Furlo, Italy. The impact melt lithologies have an andesitic composition with significantly varying contents of Al, Ca, and alkali elements. Their present day 87Sr/86Sr ratios cluster at about 0.7085, and 143Nd/144Nd ratios range from 0.5123 to 0.5125. Compared to the melt lithologies that stayed inside the crater, data for ejecta material show larger variations. The 87Sr/86Sr ratios range from 0.7081 for chloritized spherules from La Lajilla to 0.7151 for sanidine spherules from Furlo. The 143Nd/144Nd ratio is 0.5126 for La Lajilla and 0.5120 for the Furlo spherules. In an tCHUR(Nd)-tUR(Sr) diagram, the melt lithologies plot in a field delimited by Cretaceous platform sediments, various felsic lithic clasts and a newly found mafic fragment from a suevite. Granite, gneiss, and amphibolite have been identified among the fragments from crystalline basement gneiss. Their 87Sr/86Sr ratios range from 0.7084 to 0.7141, and their 143Nd/144Nd ratios range from 0.5121 to 0.5126. The TNdDM model ages vary from 0.7 to 1.4 Ga, pointing to different source terranes for these rocks. This leads us to believe that the geological evolution and the lithological composition of the Yucatán basement is probably more complex than generally assumed, and Gondwanan as well as Laurentian crust may be present in the Yucatán basement.
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The Morávka meteorite fall: 3. Meteoroid initial size, history, structure, and compositionThe properties and history of the parent meteoroid of the Morávka H5-6 ordinary chondrites have been studied by a combination of various methods. The pre-atmospheric mass of the meteoroid was computed from fireball radiation, infrasound, seismic signal, and the content of noble gases in the meteorites. All methods gave consistent results. The best estimate of the pre-atmospheric mass is 1500 +/- 500 kg. The fireball integral bolometric luminous efficiency was 9%, and the acoustic efficiency was 0.14%. The meteoroid cosmic ray exposure age was determined to be (6.7 +/- 1.0) x 106 yr. The meteorite shows a clear deficit of helium, both 3He and 4He. This deficit can be explained by solar heating. Numerical backward integration of the meteoroid orbit (determined in a previous paper from video records of the fireball) shows that the perihelion distance was probably lower than 0.5 AU and possibly as low as 0.1 AU 5 Ma ago. The collision which excavated Morávka probably occurred while the parent body was on a near-Earth orbit, as opposed to being confined entirely to the main asteroid belt. An overview of meteorite macroscopic properties, petrology, mineralogy, and chemical composition is given. The meteorites show all mineralogical features of H chondrites. The shock level is S2. Minor deviations from other H chondrites in abundances of trace elements La, Ce, Cs, and Rb were found. The ablation crust is enriched with siderophile elements.
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The Morávka meteorite fall: 2. Interpretation of infrasonic and seismic dataThe sound production from the Morávka fireball has been examined in detail making use of infrasound and seismic data. A detailed analysis of the production and propagation of sonic waves during the atmospheric entry of the Morávka meteoroid demonstrates that the acoustic energy was produced both by the hypersonic flight of the meteoroid (producing a cylindrical blast wave) and by individual fragmentation events of the meteoroid, which acted as small explosions (producing quasi- spherical shock waves). The deviation of the ray normals for the fragmentation events was found to be as much as 30 degrees beyond that expected from a purely cylindrical line source blast. The main fragmentation of the bolide was confined to heights above 30 km with a possible maximum in acoustic energy production near 38 km. Seismic stations recorded both the direct arrival of the airwaves (the strongest signal) as well as air-coupled P-waves and Rayleigh waves (earlier signals). In addition, deep underground stations detected the seismic signature of the fireball. The seismic data alone permit reconstruction of the fireball trajectory to a precision on the order of a few degrees. The velocity of the meteoroid is much less well-determined by these seismic data. The more distant infrasonic station detected 3 distinct signals from the fireball, identified as a thermospheric return, a stratospheric return, and an unusual mode propagating through the stratosphere horizontally and then leaking to the receiver.
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The Morávka meteorite fall: 4. Meteoroid dynamics and fragmentation in the atmosphereDetailed analysis of the fragmentation of the Morávka meteoroid during the atmospheric entry is presented. The analysis is based on the measurement of trajectories and decelerations of fragments seen in a video and at the locations of energetic fragmentation events from seismic data obtained at several stations in the vicinity of the fireball trajectory. About 100 individual fragments are seen on video frames. Significant deceleration of the fireball at heights of ~45 km revealed that the meteoroid had already fragmented into ~10 pieces with masses of 100-200 kg, though the fireball still appeared as a single object. At heights of 37-29 km, all primary fragments broke-up again under dynamic pressures up to 5 MPa. The cascade fragmentation then continued, even though smaller pieces breaking off from the larger masses were increasingly decelerated and the dynamic pressure acting upon them decreased. At each fragmentation, a significant part of the mass was lost in the form of dust or tiny particles. This was the dominant process of mass loss. The continuous ablation due to melting and evaporation of the meteoroid surface was less efficient with a corresponding ablation coefficient of only 0.003 s^2 km^(-2). During fragmentation, some pieces achieved lateral velocities up to 300 m/s, about an order of magnitude more than can be explained by aerodynamic loading. The fragmentation continued even after ablation ceased, as demonstrated by the incomplete fusion crust covering all recovered fragments. We estimate that several hundreds of meteorites of a total mass of ~100 kg landed, mostly in a mountainous area not suitable for systematic meteorite searches. Six meteorites with a total mass of 1.4 kg were recovered up to the end of May 2003. Their positions are consistent with the calculated strewn field.
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Analysis of a "flickering" Geminid fireballIn the early morning hours of December 13, 2002, a bright Geminid fireball with an absolute magnitude of -9.2 +/- 0.5 was observed from Southern Saskatchewan, Canada. The fireball displayed distinct small-scale oscillations in brightness, or flickering, indicative of the parent meteoroid being both non-spherical and rotating. Using the light curve derived from a calibrated radiometer, we determine a photometric mass of 0.429 +/- 0.15 kg for the meteoroid, and we estimate from its initial rotation rate of some 6 Hz that the meteoroid was ejected from the parent body (3200) Phaethon some 2500 +/- 500 years ago. We find that 70% of Geminid fireballs brighter than magnitude -3 display distinct flickering effects, a value that is in stark contrast to the 18% flickering rate exhibited by sporadic fireballs. The high coincidence of flickering and the deep atmospheric penetration of Geminid fireballs are suggestive of Geminid meteoroids having a highly resilient structure, a consequence, we suggest, of their having suffered a high degree of thermal processing. The possibility of Gemind material surviving atmospheric ablation and being sampled is briefly discussed, but the likelihood of collecting and identifying any such material is admittedly very small.
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The Morávka meteorite fall: 1. Description of the events and determination of the fireball trajectory and orbit from video recordsThe Morávka (Czech Republic) meteorite fall occurred on May 6, 2000, 11:52 UT, during the daytime. Six H56 ordinary chondrites with a total mass of 1.4 kg were recovered. The corresponding fireball was witnessed by thousands of people and also videotaped by 3 casual witnesses. Sonic booms were recorded by 16 seismic stations in the Czech Republic and Poland and by one infrasonic station in Germany. A total of 2.5% of the fireball eyewitnesses reported electrophonic sounds. Satellites in Earth orbit detected part of the fireball light curve. In this first paper from a series of 4 papers devoted to the Morávka meteorite fall, we describe the circumstances of the fall and determine the fireball trajectory and orbit from calibrated video records. Morávka becomes one of only 6 meteorites with a known orbit. The slope of the trajectory was 20.4 degrees to the horizontal, the initial velocity was 22.5 km/s, and the terminal height of the fireball was 21 km. The semimajor axis of the orbit was 1.85 AU, the perihelion distance was 0.982 AU, and the inclination was 32.2 degrees. The fireball reached an absolute visual magnitude of -20 at a height of 33 km.