The orbit,atmospheric dynamics,and initial mass of the Park Forest meteorite

Abstract— The fireball accompanying the Park Forest meteorite fall (L5) was recorded by ground‐based videographers, satellite systems, infrasound, seismic, and acoustic instruments. This meteorite shower produced at least 18 kg of recovered fragments on the ground (Simon et al. 2004). By combining the satellite trajectory solution with precise ground‐based video recording from a single site, we have measured the original entry velocity for the meteoroid to be 19.5 ± 0.3 km/s. The earliest video recording of the fireball was made near the altitude of 82 km. The slope of the trajectory was 29° from the vertical, with a radiant azimuth (astronomical) of 21° and a terminal height measured by infrared satellite systems of 18 km. The meteoroid's orbit has a relatively large semi‐major axis of 2.53 ± 0.19 AU, large aphelion of 4.26 ± 0.38 AU, and low inclination. The fireball reached a peak absolute visual magnitude of ?22, with three major framentation episodes at the altitudes of 37, 29, and 22 km. Acoustic recordings of the fireball airwave suggest that fragmentation was a dominant process in production of sound and that some major fragments from the fireball remained supersonic to heights as low as ?10 km. Seismic and acoustic recordings show evidence of fragmentation at 42, 36, 29, and 17 km. Examination of implied energies/initial masses from all techniques (satellite optical, infrasound, seismic, modeling) leads us to conclude that the most probable initial mass was (11 ± 3) × 10³ kg, corresponding to an original energy of ?0.5 kt TNT (2.1 times 10¹² J) and a diameter of 1.8 m. These values correspond to an integral bolometric efficiency of 7 ± 2%. Early fragmentation ram pressures of <1 MPa and major fragmentations occurring with ram pressures of 2–5 MPa suggest that meter‐class stony near‐Earth asteroids (NEAs) have tensile strengths more than an order of magnitude lower than have been measured for ordinary chondrites. One implication of this observation is that the rotation period for small, fast‐rotating NEAs is likely to be >30 seconds.     

THE CORE OF THE QUADRANTID METEOROID STREAM IS TWO HUNDRED YEARS OLD

The Quadrantids are one of the most active annual meteor showers and have a number of unusual features. One is a sharp brief maximum, 12–14 h in length. A second is the Quadrantids, relatively recent appearance in our skies, the first observation having likely been made in 1835. Until recently no likely parent with a similar orbit had been observed and previous investigators concluded that the stream was quite old, with the stream’s recent appearance and sharp peak attributed to a recent fortuitous convergence of meteoroid orbits. The recent discovery of the near-Earth asteroid 2003 EH1 on an orbit very similar to that of the Quadrantids has almost certainly uncovered the parent body of this stream. From the simulations of the orbit of this body and of meteoroids released at intervals from it in the past, we find that both the sharp peak and recent appearance of the Quadrantids can most easily be explained assuming meteoroids were ejected in substantial numbers near 1800 AD.     

Mud diapirism: the origin of melanges in accretionary complexes?

Chaotic melange deposits, a mixture of blocks in a clay matrix, have commonly been attributed to the mechanism of submarine slumping. In the oceans at the present day slumping does not occur on a sufficiently large scale to produce the quantities of melange seen in ancient accretionary complexes. In modern accretionary complexes, massive shale diapirism produces large volumes of melange, and is an entirely adequate mechanism to account for melanges in ancient complexes.     

Characterization and P-T Evolution of Melt-bearing Ultrahigh-temperature Granulites: an Example from the Anapolis-Itaucu Complex of the Brasilia Fold Belt, Brazil

Sapphirine–quartz occurs in orthopyroxene–garnetgranulites in two areas     

The Crossite Content of Ca-Amphibole as a Guide to Pressure of Metamorphism

A correlation between the crossite component (NaM₄) in Ca-amphiboleand pressure of metamorphism has long been recognized (Shido& Miyashiro, 1959), but only recently has the reaction beenidentified which buffers this aspect of amphibole composition(Brown, 1974): Ca-amphibole+iron oxide+albite+chloriteI+H₂O (±stilp,qtz) = crossite+epidote (±muscovite, qtz). The exact stoichiometry of the reaction depends on compositionalvariables in the minerals, especially Fe²⁺/Mg and Fe³⁺/Al. Ca-amphiboleshould have fixed NaM₄, at any given T and P, where it coexistswith iron oxide, albite, and chlorite. Comparison of Ca-amphibole composition with mineral assemblage,in rocks from Otago, N.Z., and elsewhere, supports this hypothesis.In any terrane NaM₄ is nearly constant at a particular metamorphicgrade where amphibole exists in the buffering assemblage, butvaries widely outside of this assemblage. Variations in Fe²⁺/Mgand Fe³⁺/Al in the amphibole have relatively little effect onNaM₄, but in high pressure amphiboles NaM₄ varies inverselywith Al^iv. Ca-amphiboles from high pressure areas have substantially moreNaM₄ (Otago, 0.6 of 2.0) than those from lower pressure areas(Sierra contact aureoles, 0.1). These relations suggest thatin the buffering assemblage, the NaM₄ content of Ca-amphiboleshould be a useful relative barometer for low to medium grademetamorphic rocks.     

GRAPHICS FOR LINEARITY AND SELECTIVITY AND PREDICTION DIAGNOSTICS FOR MULTICOMPONENT SPECTRA

Modern scanning infrared reflectance/absorption spectroscopes measure absorptions or reflectance at asequence of around 1000 wavelengths. Training data may consist of 10-100 carefully designed samplemixtures whose true compositions are either known by formulation or accurately determined by wetchemistry. In future, one wishes to predict the true composition of a newly presented sample from itsspectrum. Varying compositions of a mixture of three sugars in water are used for illustration of severaldifferent graphical techniques; the spectral measurements here are near-infrared (NIR) absorbances, butthere is nothing exclusively infrared about the methodology. Graphs display the adequacy of a linearexplanation of absorbance variability at each wavelength by wavelength linearity plots. These highlightregions of the spectrum where non-linearities and interaction effects are substantial. By selecting out thesesubstantially non-linear regions, one can concentrate on linear formulae for prediction with resultantrobust linear modelling. Such selections are further aided by plots which identify the component sugarfor which each wavelength is most selective. Such plots offer rather natural pre-screening as an alternativeor supplement to the wavelength selection method of Brown. We also display prediction diagnostics (R, Rx) which on a sample-by-sample basis may diagnose aparticularly unusual presented spectrum. These diagnostics are shown to have predictive import for avalidation data set.     

Fe XVIII EMISSION LINES IN SOLAR X-RAY SPECTRA

We have calculated intensity ratios for emission lines of Fexviii in the 13–94 Å wavelength range at electron temperatures characteristic of the solar corona, T _e = 2–10 x 10⁶ K. Our model ion includes data for transitions among the 2s ²2p ⁵ , 2s2p ⁶, 2s ²2p ⁴3l, and 2s2p ⁵3l (l = s, p, and d) states. Test calculations which omit the 2s2p ⁵3l levels show that cascades from these are important. We compare our results with observed ratios determined from four solar X-ray instruments, a rocket-borne spectrograph, and spectrometers on the P78–1, OV1–17 and Solar Maximum Mission (SMM) satellites. In addition, we have generated synthetic spectra which we compare directly with flare observations from SMM. Agreement between theory and observation is generally quite good, with differences that are mostly less than 30%, providing limited support for the accuracy of the atomic physics data used in our calculations. However, large discrepancies are found for ratios involving the 2s ²2p ^{5 2}P_3/2- 2s2p ^{6 2}S line at 93.84 Å, which currently remain unexplained. Our analysis indicates that the FeXVIII feature at 15.83 Å is the 2s ²2p ^{5 2}P_3/2 - 2s ²2p ⁴(³P)3s ⁴P_3/2 transition, rather than 2s ²2p ^{5 2}P_3/2 - 2s ²2p ⁴(³P)3s ²P_3/2, as suggested by some authors.