Different Directions

Different Directions

The Pultusk Shower

A high, historic fall from Poland!

At 7 pm near the town of Pultusk, thousands of people witnessed a large fireball followed by detonations and a very large shower of small fragments in an area of about 127 sq km.

 

Meteorite breaking up.

Figure 1. Meteorite breaking up.

 

The Pultusk meteorite is one of the largest stony meteorite showers recorded in history.

And we are lucky to have one of the stones. Here's our education sample, 84 grams with a great fusion crust:

 

Pultusk, 84 grams.

Figure 2.

 

Pultusk is a historical meteorite fall because it was the largest known meteorite shower on record. An estimated 2000kg fell a few miles north of Warsaw, Poland. Many of the stones were very small and a single stone from the fall is often referred to as a "Pultusk pea."

According to Norton (1998), the meteoroid became visible at an altitude of almost 200 miles, which also makes it the highest fireball on record seen by the naked eye! The point at which the meteoroid ceased to generate light was about 25 miles.  This resulted in an unusually wide fall path and meteorite fragments resembling Pultusk were found in Madagascar, Italy and Russia.

Here's a map of its strewn field:

 

Pultusk, Strewnfield.

Figure 3.

 

The Pultusk meteorite is a veined and brecciated chondrite with abundant xenoliths with various degrees of recrystallization.

Like all stony meteorites that had not been modified due to melting or differentiation of a parent body, Pultusk formed when various types of dust and small grains present in the early solar system accreted to form primitive asteroids.

Pultusk has been classified an H5 because of its high iron content, and many researchers feel that its parent body, and for all H5 chondrites, is the S-type asteroid 6 Hebe, with less likely candidates being 3 Juno and 7 Iris.

 

Hebe Model.

Figure 4. 6 Hebe modeled.

As you can see, 6 Hebe is cratered by impacts and quite deformed, but the large Pultusk fall was the result of impacts of small near-earth asteroids broken off from 6 Hebe in the past – not from a direct impact on 6 Hebe.

The H chondrites have very similar trace element abundances and Oxygen isotope ratios to the IIE iron meteorites, making it likely that they both originate from the same parent body.

The chondrules in Pultusk have been subjected to heat and pressure so that their contours are frequently difficult to distinguish.

Analysis of Pultusk show that olivine and bronzite are the main minerals with Kamacite, troilite and chromite also part of its composition.

Just The Specs

Jan 30 - 142th Anniversary (1868 - 2010), Pultusk Meteorite Shower in Poland.

H5 Veined & Brecciated Chondrite with abundant Xenoliths.

Fall January 30, 1868.Pultusk, Poland.

Composition:

  • Meteorite iron, kamacite – occurs as gray grains of various shape and size.
  • Troilite – forms fractured grains. Occurs with kamacite and as inclusions in it.
  • Chalcopyrite – appears rarely, occurs with troilite.
  • Chromite – occurs relatively rarely as inclusions in silicate minerals, its grains are also fractured.
  • Native copper – forms tiny inclusions in kamacite.
  • Olivine – a component of the chondrules and occurs in the groundmass.
  • Pyroxene – bronzite, a component of the chondrules and in subordinate amounts present in the groundmass.
  • Plagioclases – fractured grains with twinning.
  • Maskelynite – a glass that is only formed by extremely high-velocity impacts.

    Scientists used Maskelynite (See Terms) to determine that the Lonar crater in Maharashta, India - around 6,000 feet wide and 500 feet deep - was caused by an asteroid

Side Trip – More on H chondrites

The H type ordinary chondrites are the most common type of meteorite.

The name comes from their High iron abundance, with respect to other ordinary chondrites, which is about 25-31% by weight and present in metallic form. H chondrites are thus strongly magnetic despite their stony chondritic appearance.

A probable parent body for this group is 6 Hebe, although it could also be 3 Juno and 7 Iris. These meteorites arise from impacts on small near-earth asteroids broken off from 6 Hebe, rather than originating from 6 Hebe directly.

The H chondrites have very similar trace element abundances and Oxygen isotope ratios to the IIE iron meteorites, making it likely that they both originate from the same parent body.

The most abundant minerals are bronzite (an orthopyroxene), and olivine. Characteristic is the fayalite (Fa) content of the olivine. H chondrites also 15-19% of nickel-iron metal and about 5% of troilite.

Most of these meteorites have been significantly metamorphosed.

Historically, the H chondrites have been named bronzite chondrites or olivine bronzite chondrites for the dominant minerals, but these terms are considered obsolete, and only still used at a few vendor sites.

Terms

As we have seen with other meteorites, Pultusk is a historic chondrite with some unique features. Here's some of the terms used to describe the meteorite.

 

Definition of Breccia

  1. n. A course-grained rock, composed of angular, broken rock fragments held together by a mineral cement or a fine-grained matrix.

Here's an example:

 

Breccia.

Photo from http://plone.jcu.edu.au/ees/Members/jc135592/breccias-and-brecciation-mechanisms

 

Definition of Chondrite

  1. n. A meteoric stone characterized by the presence of chondrules.

Definition of Chondrule

  1. n. A peculiar rounded granule of some mineral, usually enstatite or chrysolite, found embedded more or less abundantly in the mass of many meteoric stones, which are hence called chondrites


Chondrite with Chondrules.

Photo from http://www.geokem.com/meteorites.html

 

Definition of Maskelynite

  1. n. A type of impact created glass.

Here's a sample of feldspar that has been subjected to impact pressures and converted to Maskelynit.

 

bedout-maskelynite.

Thin section is from a breccia-zone sample showing feldspar laths (yellow-brown in plane light due to alteration).  Under crossed-nicols (A Nicol prism is a type of polarizer, an optical device used to generate a beam of polarized light.) the feldspars are black at all orientations, indicating that they have been converted into Maskelynite (M) - glass produced when plagioclase is subjected to pressures only produced under impact conditions (after Becker et al., 2004).

http://records.viu.ca/~earles/bedout-jun04.htm

 

Definition of Troilite

  1. n. Native iron protosulphide, FeS. It is known only in meteorites, and is usually in embedded nodular masses of a bronze color.

Here's a picture of a troilite inclusion:

 

Troilite Inclusion Within Iron Inclusion.

Photo from http://www.lexic.us

 

Definition of Xenolith

  1. n. (Greek: 'foreign rock') A rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. Here's a picture.

 

Xenolith.

A xenolith in a granite; eastern Sierra Nevada, Rock Creek Canyon, California.

Wikimedia Commons.

 

Links

Here's an article about the asteroid Hebe:

http://en.wikipedia.org/wiki/6_Hebe

 

Here's a fascinating article about the lake in Lonar Crater. The uniqueness of the lake is it’s salinity and alkalinity. However, the crater is about 50,000 years old and roughly the same size and age as Meteor Crater, in Arizona, USA.

http://en.wikipedia.org/wiki/Lonar_crater_lake

 

Lonar Crater.

http://probaway.wordpress.com/2008/05/28/tunguska-event/

 

Here's the International Meteorite Collectors Association (IMCA):

http://imca.repetti.net/metinfo/index.html

 

Here's two dictionaries for reference:

http://www.science-dictionary.org/

Lexic also includes excellent pictures:

http://www.lexic.us/

 

Figures & Acknowledgments

 

Figures

Figure 1. Photo from http://www.uocmas.info/Picture_Day/Pictures/20091015.png

Figure 2. Photo by New England Meteoritical Services. www.meteorlab.com

Figure 3. Distribution ellipse of the Pultusk meteorite fall, Poland, 1868. Wikimedia Commons.

Figure 4. Image from http://www.starrynightsupport.com/support_trio/modules/KB/html.php


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