Wyniki wyszukiwania - Biblioteka Nauki

1

Time of fall and some properties of the Morasko meteorite

100%

Stankowski W. , Muszyński A.

Materials Science Poland

|

2008

|

tom Vol. 26, No. 4

897--902

EN

The time of fall of a meteorite and the appearance of the impact craters in Morasko have been documented by the thermoluminescene method, 14C dating, as well as palynological estimation. The extraterrestrial effect on the lithology and morphology of Moraska Góra (Morasko Hill) took place about 5000 years BP. Morasko meteorite is composed in about 98 wt. % of Fe--Ni alloy and in about 2 wt. % of dark FeS nodules, up to 20 mm in diameter. The principal Fe--Ni alloy is kamacite with nearly 6% Ni and taenite with up to 30% of Ni. FeS occurs as troilite, being often wrapped up by rounded flakes of graphite.

2

Kratery meteorytowe na Marsie

80%

Hurnik H.

Acta Societatis Metheoriticae Polonorum

|

2011

|

tom 2

40-56

EN

Meteorite craters, volcanoes and deep valleys are main obiects of Mars topography. The are many tausend or millions of craters and they are very different, with diameters of only centimeters to big basins with diameters of 25oo kilometers. The age of oldest craters on Mars is about 3,9 billions year.

3

Spectral scaling in Mars topography: effect of craters

80%

Nikora V. , Goring D.

Acta Geophysica

|

2006

|

tom Vol. 54, no. 1

100-112

EN

Extensive computer simulations aimed at testing a hypothesis that impact craters may explain the scaling behaviour of surface spectra are presented. The simulations show that indeed crater effects alone may explain the spectral scaling of Mars’ topography revealed from MOLA data. The range of the scaling exponents obtained for a wide range of simulation parameters does not exceed the limits observed for Mars. The simulations suggest that the shape of large craters is the key factor lead-ing to the two scaling ranges in the surface spectra. Particular values of the scaling exponents may additionally depend on the depth-diameter relationship and the crater size distribution.

4

Identyfikacja kraterów uderzeniowych ze względu na rodzaj środowiska

80%

Brachaniec T. , Brom K.

|

2015

|

tom 6

26-33

EN

It seems that the only correct way to identify impact craters is a combination of theoretical analysis, visual observation and experimental analysis, which are inextricably linked to the environment in which the crater was formed. Undoubtedly, the shock metamorphism is an essential diagnostic tool for the identification of the crater. The depth of water is a major problem in the formation of the marine craters.

5

Początki badań impaktów

70%

Brachaniec T.

Acta Societatis Metheoriticae Polonorum

|

2013

|

tom 4

9-21

EN

Impacts geology is a multi-disciplinary science, focus aspects of meteoritics, astronomy, petrography, geochemistry, structural geology, sedimentology and geophysics. The first studies of craters began in the 60s. Significant events in the development of this science were: the first research of the Cosmos, development of mineralogical and geochemistry analysis and important papers. Significant progress in the development of research studies reflect the number of newly discovered craters. Many aspects associated with them, such as dating, strewnfields, water impacts are still fairly problematic.

6

Analiza cech impaktu ukośnego na przykładzie struktur Porządzie, Jaszczułty i Ochudno

60%

Walesiak T.

|

2016

|

tom 7

151-176

EN

It’s considered that one half of all projectiles are striking surface of planets at the angle lower than 45°. Our knowledge of oblique impact events is based on computer modelling, laboratory experiments and observation of craters on the Moon, Mars, Venus and other celestial bodies. Recent discovery in northeast Poland, reveals at least four structures with features reserved for low-angle impacts. In this article we show and explain them using high-quality laser air scanning data (LiDAR) in comparison to results of experiments and similar real known objects on other planets. Also we try to verify by analyzing historical sources if multiple impact event could occur in our area and, if it was noticed and reported in the papers.

7

Przegląd najważniejszych prac dotyczących próby ustalenia daty spadku meteorytów oraz wieku kraterów Morasko

51%

Walesiak T.

Acta Societatis Metheoriticae Polonorum

|

2021

|

tom 12

129-148

EN

One of criteria suggesting impact origin may be recognition of extraterrestrial matter inside or around suspected cavities. In case of Morasko some dating results throw doubt on link between craters and meteorites. Conclusion of some past research papers was that cavities were formed about 5 ka BP (e.g. palynological investigation, luminescence dating), while more or less facts testify fall in the Middle Ages (e.g. “young” charcoal pieces in crust of meteorites or shrapnel stuck in the roots of old tree). In this paper we perform comprehensive analysis of each result and check if there exists alternative explanation. During past palynological investigation, there were examined two craters. It was concluded that beginning of accumulation of sediments in smaller cavity started 5500–5000 BP. However, pollen spectrum for largest basin was different suggesting younger age. The problem is that according to bathymetric maps, samples could be collected from inner uplift (similar feature was observed inside Porzadzie and Jaszczulty, unconfirmed impact structures yet). If we compare profiles from craters with recent research (palynological study supported by radiocarbon dating) on sediments in Lake Strzeszynskie (6 km SW from Morasko) pollen spectrum seems to be similar more to results dated to <1000 BP. Especially percentage of non-arboreal pollen for both examined Morasko craters is much higher (5 times greater than it was for layer dated to 5 ka BP in Lake Strzeszynskie). Possibility of short disturbance (related to impact) cannot be excluded, but in such case any time of event should be taken into account. For small lakes (like those filling the craters) also local conditions could play important role. Analysis of luminescence dating may also discuss past conclusions. OSL method applied for samples taken from the thin layer of sand in the bottom of largest structure (under 3,9 m of organic sediments filling the crater) suggested age 5–10 ka BP for 24 aliquots. Same number of samples (24) revealed age 0–5 ka BP (13 samples with age <3 ka BP including several younger than 1 ka BP). Older dates can be explained by partial or even no zeroing, but last contact with light (zeroing signal) of sand grains (excavated from depth of almost 4 meters under organic matter) seems that might occur only during (or shortly after) the impact. It is difficult to find convincing arguments, which can undermine initial radiocarbon dating giving age <1 ka BP for 7 of 9 samples taken from the bottom layer of organic sediments from three Morasko craters. Same issue may exist with small charcoal pieces with age <2 ka BP (and several dated to ~700 BP) discovered deep in sinter-weathering crust of meteorites. Study of charcoal particles excluded their origin during post-sedimentary processes (like forest fire) unless meteorite fragments were laying directly on the surface for period between impact and wildfire (surviving whole time inhospitable climate conditions). There are two other possible explanations of charcoals. Either they were present at location as a result of past forest fire or they were produced during impact. However, similar small charcoal pieces were discovered around many craters (Kaali, Ilumetsa, Campo del Cielo, Whitecourt) and they were successfully used to estimate maximum age of those structures. During second stage of 14C dating the age obtained from three samples (taken few centimeters above the mineral bottom) was estimated ~5 ka BP. Looking for answer why these results are so different from previous once there may be mentioned at least two options. Lake sediments is difficult matter for radiocarbon dating and results may be hundreds or even thousands years older than real age. Second explanation may be that older matter (remnant of trees, paleosoil etc.), distributed around craters during impact, could be displaced by wind, rain, erosion and trapped in the bottom of cavities. The argument, which may be also against hypothesis of impact ~5 ka BP is meteorite shrapnel stuck in the roots of old tree. Result of expertise showed, that there exists mechanical damage in the wood and the only possible explanation is that meteorite has hit living tree. Maximum age, that this type of wood may preserve (inside building) is 1,8 ka while in natural environment not more than 500 years. Anyway some further examinations should be performed. The age obtained during AMS 14C dating of 2 samples from thin layer of paleosoil, discovered under overturned flap around largest Morasko crater, was ~5 ka BP. Observation that preserved layer of paleosoil is approximately 3 times thinner than thickness of modern soil may lead to conclusion that during impact top (younger) layer of organic sediments was removed and only older part “survived” in few locations close to the rim. The conclusion of the research was that dating provides maximum age of the impact (which does not exclude much younger impact <1 ka BP) so could be considered as right explanation of past discrepancies.

8

Ekspansja pustki kulistej w nieściśliwym ośrodku sprężysto-idealnie plastycznym

51%

Włodarczyk E. , Głodowski Z.

Biuletyn Wojskowej Akademii Technicznej

|

2005

|

tom Vol. 54, nr 11

77-90

PL

Skonstruowano analityczne rozwiązanie problemu ekspansji kulistej pustki w w nieściśliwym ośrodku sprężysto-idealnie plastycznym. Ekspansję wymuszono skokowym radialnym napędzeniem powierzchni pustki do początkowej prędkości v₀. Określono analitycznie stan naprężenia w ośrodku otaczającym pustkę. Wprowadzono zamknięte wzory na maksymalne promienie odkształconych plastycznie kawerny i otaczającej ją warstwy ośrodka. Jak się okazuje, za pomocą tak uproszczonego modelu można szacować średnią wartość średnicy krateru od nieodkształcalnego pocisku uderzającego w metalową tarczę z umiarkowaną (do 800 m/s) prędkością v₀.

EN

It has been constructed an analytic solution of a problem of expansion of a spherical void in incompressible elasto-ideal plastic medium. The expansion was forced by a radial jumpwise acceleration of a void surface up to the initial velocity v₀. The stress state in the medium surrounding the void has been determined. The closed formulae for the maximal radius of the plastically deformed cavity and the medium layer surrounding it have been derived. It was found that using this simplified model one can estimate the mean value of the crater diameter due to the projectile striking on a metal target with the moderate velocity v₀ (up to 800 m/s).