- Tytuł:
-
Kratery Morasko – obrona hipotezy ukośnego impaktu w kontekście dostępnej wiedzy i wyników badań
Morasko craters – in defense of oblique impact origin based on knowledge and research - Autorzy:
- Walesiak, Tomasz
- Powiązania:
- https://bibliotekanauki.pl/articles/1830330.pdf
- Data publikacji:
- 2021
- Wydawca:
- Polskie Towarzystwo Meteorytowe
- Tematy:
-
bilateral symmetry
crater field
elliptical craters
forbidden zone
meteorite Morasko
oblique impact - Opis:
- Over 2 years ago there was published an article (Bronikowska 2018a) challenging some results of research related to Morasko meteorite fall. Those results are huge problem for scientists who are not able to explain them using simplified models and maybe do not want to admit that some assumptions should be verified and redefined. One of hypothesis discussed in the paper was article manifesting that Morasko craters were created during oblique impact (Walesiak 2017) and that initial trajectory can be estimated by elongation of almost all cavities, their bilateral symmetries according to longer axis and observed asymmetries of rims. By comparison to Campo del Cielo craters Walesiak suggested that impact angle could be very shallow (10–20°), as ellipticity of all smaller Morasko structures is approx. 1,3. Further analysis of topography in neighborhood of Morasko revealed that there may exist more impact craters around this area, which may explain discovery of two iron meteorites near Oborniki village (17 km NW from Meteorite Morasko Restricted Area), unfortunately lost during World War II. In fact, Bronikowska confused definitions “oblique impact” and “elliptical craters”, what can be supported by given references (Elbeshausen et al. 2009) confirming Walesiak hypothesis. Unfortunately, this misunderstanding touches also another article of this author (Bronikowska et al. 2017), where obliquity was neglected. However, estimated during that modeling pre-impact angle (30–43°), according to known definitions written in many publications, should be classified as oblique impact. All elongated craters, as well as morphology of the largest structure in Meteorite Morasko Restricted Area suggest impact from NW while during reconstruction of meteoroid parameters Bronikowska assumed impactor coming from NE (based on existing strewn field). Considering not clear relation between meteorites and craters (e.g., lack of findings in cavities, relatively poor number of shrapnel fragments around structures and possibility that craters may be much older than fall of meteorites), it may be not enough reliable justification. Even if relation exists, example of Whitecourt (with distribution of meteorites downrange), compared with abundance of Morasko shrapnel fragments collected hundreds of meters NE from Restricted Area, undermines parameter used in modelling. Also, single fragmentation is doubtful, concluded after unreasonable omitting known craters outside Restricted Area (e.g., crater no 8 described by Pokrzywnicki (1964) and structure no 9 mentioned by Hodge (1994)). Finally, use of iSALE-2D shock physics code (valid for vertical impacts only) for modelling of elliptical craters formed during highly oblique impact (angle lower than 12°), even considering vertical component (which approximation is only applicable for impact into materials with a friction coefficient of about f=0,7 with no or very little cohesion) (Elbeshausen et al. 2009), also should not be considered as proper applied method leading to get valuable results. In this article there is proposed new strewn field definition for Morasko meteorite, based on elongation of all known and unconfirmed (yet) craters. Surprisingly, estimated (redefined) pre-impact trajectory gives convincing explanation for bilaterally symmetrical distribution of documented findings.
- Źródło:
-
Acta Societatis Metheoriticae Polonorum; 2021, 12; 108-128
2080-5497 - Pojawia się w:
- Acta Societatis Metheoriticae Polonorum
- Dostawca treści:
- Biblioteka Nauki
Artykuł