Directional Distribution of Observable Comets Induced by A Star Passage Through the Oort Cloud

We simulated the passage of a star through the Oort cometary cloud andanalyzed the resulting sample of observable long period comets, noting strong asymmetries in the directional distribution of the perihelion points of thosecomets. We discuss the results previously published byWeissman (1996) for the same case. An explanation is suggestedwhy the isotropic output can be obtained only for a very peculiar case. The``cometary shower' density variation with time is also presented and thetime-dependence of the directional distribution is discussed.     

Impact Break-Up of Cometary Nuclei – Conclusions from Impact Experiments

Experiments of impact-generated break-up of icy and icy/mineral targets were performed. Formulae for the velocity of ejecta and for energy of disruption were fitted to the experimental data. An assumption that these formulae can be extrapolated for kilometer-size bodies enabled us to discuss the consequences of impacts on cometary nuclei and on planetesimals. It was found that the porosity of the targets as well as their composition (mineral to total mass ratio), are the crucial parameters.     

ChemiX: a Bragg crystal spectrometer for the <Emphasis Type="Italic">Interhelioprobe</Emphasis> interplanetary mission

Interhelioprobe (IHP), an analogue to the ESA Solar Orbiter, is the prospective Russian space solar observatory intended for in-situ and remote sensing investigations of the Sun and the inner heliosphere from a heliocentric orbit with the perihelion of about 60 solar radii. One of several instruments on board will be the Bragg crystal spectrometer ChemiX which will measure X-ray spectra from solar corona structures. Analysis of the spectra will allow the determination of the elemental composition of plasma in hot coronal sources like flares and active regions. ChemiX is under development at the Wroc?aw Solar Physics Division of the Polish Academy of Sciences Space Research Centre in collaboration with an international team (see the co-author list). This paper gives an overview of the ChemiX scientific goals and design preparatory to phase B of the instrument development.     

Observations of the Ly-α Forest

We analyze four high resolution rich samples of Ly-α and metal lines (two at z ≥ 2 and two at z ≤ 0.2). We describe evolution of the observed Doppler parameters and absorbers separation and propose a model of the forest. We argue that all absorption lines are formed in gaseous caustics created in stable DM subclouds. The absorption lines are described by two local characteristics, the Doppler parameter and the column density of neutral hydrogen. We show that evolution of the Doppler parameter is very slow and its mean value increases by a factor ≤1.5 at redshifts 0 ≤ z ≤ 3. We show that absorbers separation increases as <d_sep ∝ (1 + z)?2. We describe evolution of absorbers in the framework of a two component model: the first population represents absorbers with just one line created in compact stable DM clouds with random spatial distribution, and the second population includes absorbers with two, three and more absorption lines formed in more massive and extended random DM clouds. Slow evolution of the Doppler parameter indicates high stability of caustics and conditions within clouds. For absorbers of the second population relative velocity of lines slowly increases with time.     

Multiphase magmatic activity in the Variscan Kłodzko–Złoty Stok intrusion,Polish Sudetes: evidence from SHRIMP U–Pb zircon ages

International Journal of Earth Sciences - The Kłodzko–Złoty Stok intrusion (KZSI), located in the NE part of the Bohemian Massif of Central Europe, has preserved records of the...     

Protomylonite evolution potentially revealed by the 3D depiction and fractal analysis of chemical data from a feldspar

Tourmalinization associated with peraluminous granitic intrusions in metapelitic host-rocks has been widely recorded in the Iberian Peninsula, given the importance of tourmaline as a tracer of granite magma evolution and potential indicator of Sn-W mineralizations. In the Penamacor-Monsanto granite pluton (Central Eastern Portugal, Central Iberian Zone), tourmaline occurs: (1) as accessory phase in two-mica granitic rocks, muscovite-granites and aplites, (2) in quartz (±mica)-tourmaline rocks (tourmalinites) in several exocontact locations, and (3) as a rare detrital phase in contact zone hornfels and metapelitic host-rocks. Electron microprobe and stable isotope (δ¹⁸O, δD, δ¹¹B) data provide clear distinctions between tourmaline populations from these different settings: (a) schorl–oxyschorl tourmalines from granitic rocks have variable foititic component (^X□ = 17–57 %) and Mg/(Mg + Fe) ratios (0.19–0.50 in two-mica granitic rocks, and 0.05–0.19 in the more differentiated muscovite-granite and aplites); granitic tourmalines have constant δ¹⁸O values (12.1 ± 0.1 ‰), with wider-ranging δD (?78.2 ± 4.7 ‰) and δ¹¹B (?10.7 to ?9.0 ‰) values; (b) vein/breccia oxyschorl [Mg/(Mg + Fe) = 0.31–0.44] results from late, B- and Fe-enriched magma-derived fluids and is characterized by δ¹⁸O = 12.4 ‰, δD = ?29.5 ‰, and δ¹¹B = ?9.3 ‰, while replacement tourmalines have more dravitic compositions [Mg/(Mg + Fe) = 0.26–0.64], close to that of detrital tourmaline in the surrounding metapelitic rocks, and yield relatively constant δ¹⁸O values (13.1–13.3 ‰), though wider-ranging δD (?58.5 to ?36.5 ‰) and δ¹¹B (?10.2 to ?8.8 ‰) values; and (c) detrital tourmaline in contact rocks and regional host metasediments is mainly dravite [Mg/(Mg + Fe) = 0.35–0.78] and oxydravite [Mg/(Mg + Fe) = 0.51–0.58], respectively. Boron contents of the granitic rocks are low (<650 ppm) compared to the minimum B contents normally required for tourmaline saturation in granitic melts, implying loss of B and other volatiles to the surrounding host-rocks during the late-magmatic stages. This process was responsible for tourmalinization at the exocontact of the Penamacor-Monsanto pluton, either as direct tourmaline precipitation in cavities and fractures crossing the pluton margin (vein/breccia tourmalinites), or as replacement of mafic minerals (chlorite or biotite) in the host-rocks (replacement tourmalinites) along the exocontact of the granite. Thermometry based on ¹⁸O equilibrium fractionation between tourmaline and fluid indicates that a late, B-enriched magmatic aqueous fluid (av. δ¹⁸O ~12.1 ‰, at ~600 °C) precipitated the vein/breccia tourmaline (δ¹⁸O ~12.4 ‰) at ~500–550 °C, and later interacted with the cooler surrounding host-rocks to produce tourmaline at lower temperatures (400–450 °C), and an average δ¹⁸O ~13.2 ‰, closer to the values for the host-rock. Although B-metasomatism associated with some granitic plutons in the Iberian Peninsula seems to be relatively confined in space, extending integrated studies such as this to a larger number of granitic plutons may afford us a better understanding of Variscan magmatism and related mineralizations.     

Periglacial structures within fluvio‐aeolian successions of the end of the Last Glaciation – examples from SE Poland and NW Ukraine

The nature of permafrost and related environmental conditions in the Weichselian Late Pleniglacial and Lateglacial are reconstructed based on the assessment of frost structures that are best documented in the Loess Belt and in plateau areas composed of glacial till. Investigations were conducted in the central‐eastern part of the European Sand Belt (SE Poland and NW Ukraine) on a fluvio‐aeolian sedimentary succession and took into account its chronological context given by luminescence dating. Various generations of periglacial structures found in these deposits indicate not only the development of permafrost (ice‐wedge pseudomorphs) and decreased humidity (composite wedge casts) but also the degradation of permafrost (large‐scale involutions) and, finally, the establishment of deep seasonal frost (frost cracks). The diversity of structures in the study region appears to result from local conditions rather than increasing continentality of climate towards the east.     

The EURONEAR Lightcurve Survey of Near Earth Asteroids 2017–2020

Earth, Moon, and Planets - The Perseverance rover (Mars 2020) mission, the first step in NASA’s Mars Sample Return (MSR) program, will select samples for caching based on their potential to...