An October 1933 Witnessed Fall: Pesyanoe, Russia
The Rarest Look the Part
The year 1933 was the best ever in terms of witnessed meteorite falls. No less than 18 were reported that year which amounts to an average of one new meteorite fall every 20 days!
The picture below shows the dirty gray crust on my sample of Pesyanoe carrying with it a classic Russian Academy of Sciences meteorite label consisting numbers on cloth tape.
|In an almost never seen appearance, the gray crust of the Pesyanoe aubrite is highlighted here. Some Aubrite crust is tan, some brown, and some gray. Almost nowhere do these rarest of the rare fit the traditional characteristics of meteorites.
A total of 3393 grams of aubrite meteorite fell in the form of several stones fell on October 2nd at 6:00 in the morning constituting the 13th fall of a total of 18 falls for the year 1933. The largest single stone on this fall named Pesyanoe was 905 grams.
Unlike calcium-rich achondrites like the eucrites, Ca-poor stones including Pesyanoe have a light colored fusion crust, and in this case, the crust on Pesyanoe looks dirty gray in color.
Snow White and the Five metal nodules.
Poking out from a pearly white matrix are both enstatite crystals and a few rusting knots of metal, all hardly exemplifying 99.9% of the features found in other stone meteorites.
What’s in a Name?
The namesake and type specimen for the aubrite meteorites is the Aubres meteorite that fell near Nyons, France, on September 14, 1836. Outside the hot and cold desert finds, there are less than a dozen members of the aubrite class, with a vast majority of those witnessed to fall.
Aubrites have distinctive light-colored fusion crust, with a snowy white interior. They are usually friable stones so they crumble apart easy. Because of their high enstatite composition, aubrites are also known as enstatite achondrites.
In addition to their large white enstatite crystals, they also contain varying amounts of olivine, nickel-iron metal, and troilite, among other minerals. This arrangement of minerals in both composition and size suggests that aubrites cooled underground in their parent body under oxygen-free (reducing) conditions.
Violent impacts are likely in the aubrite’s past since the crystals are broken up and mixed around within the stone. Further, the oxygen isotopic composition of enstatite chondrites has led to the suggestion that aubrites might have formed by partial melting of an enstatite chondrite body.
A great interest to scientists is that aubrites have the highest cosmic ray exposure ages of any stony meteorites, with some estimates ranging up to 120 million years. What that means is that they have spent much time in space without any shielding help by being buried deep.
Reflectance spectra various asteroids showed similarities between the aubrite meteorites and the main belt asteroid 44 Nysa which happens to be the largest E-class asteroid as well as the brightest asteroid. The only known E-class near-earth asteroid is a suspect for the parent body of the aubrite meteorites. The asteroid, named 3103 Eger, is an Apollo and that was discovered in 1982 by Miklós Lovas who named after the city of Egerin Hungary.
From what could uncover in collection catalogues, this particular piece is the second largest sample of Pesyanoe in any collection in the world. A majority of the preserved Pesyanoe material, a sum around 1790g, still resides in the Academy of Sciences in Moscow, Russia.
This specimen also arrived to me with an elegant hand-written specimen card from the Academy of Science containing a matching specimen number.
So little Pesyanoe material has ever left Russia that this particular sample travels with both an on-specimen number, and a matching handwritten card.
Initially, when this specimen first arrived in the United States to join an institutional collection specializing in achondrites, it weighed in at 30 grams heavier. I wonder if some of those 30 grams lead to the research results published about Pesyanoe.
In an article titled Pre-Accretion and/or Regolith History of the Pesyanoe Orbite Matter and published in Lunar and Planetary Science (2003), the authors posit the following conclusions about Pesyanoe:
1. The initial Pesyanoe meteorite constrain material was contained the compounds of the essentially different irradiation and shock-thermal pre-history.
2. There are a high probability that the Pesyanoe individual En-grains fossil track characteristics refer to their history of a radiation, thermal and shock-thermal influence chiefly occurred on pre-accretion and/or regolith stages of a parent body formation of this achondrite.
3. The possible ”pure thermal” metamorphism inside a parent body, would result about the same manner in all En grains. But quite essential difference of TL-parameters, measured for the several matrix samples, indicate on very small influence of this process in comparison with the more effective and heterogeneous shock-thermal process during of exogenic reworking of this meteorite material.
4. Absence of the visual variation of concentration of some volatile-refractory elements in a number of the matrix samples of different sizes correlate with the low-level shock-thermal reworking of material consisting investigated achondrite in their metamorphic history.
5. The achondrite Pesyanoe matter during all his geology history, starting from the early irradiation in the regolith or more early environment conditions, do not underwent to influence of the shock-thermal events, stronger during the short-time interval. As it was obtained early the En group IV of the Pesyanoe probably undergoes a shock-pressure treatment with shock stage S1. This conclusion is confirmed by our TL study of experimentally shock loaded oligoclase, quartz and calcite.
In another article titled Regolith history of the aubritic meteorite parent body revealed by neutron capture effects on Sm and Gd isotopes
The authors report the following in their abstract:
Enstatite achondrites (aubrites) when compared to other stone meteorites have unusually long cosmic-ray exposure (CRE) ages. We report here the 150Sm/149Sm and 158Gd/157Gd ratios in six different structural phases, i.e., light and dark (shocked) grains and in matrix materials of Pesyanoe, in three different fragments from Pena Blanca Spring, and in one from Norton County, Shallowater, and Khor Temiki, to investigate the regolith history on the aubrite parent body.
The results from phases components of Pesyanoe confirm earlier reported evidence for regolith irradiation of several aubrites. The inferred neutron fluences for six Pesyanoe separates vary. The fluences also significantly exceed those expected from cosmic-ray irradiation during transit to Earth and approach those observed in the lunar regolith. These observations confirm that the brecciated Pesyanoe meteorite, which contains solar wind (SW) gases only in dark phases, was processed in a regolith and that structural phases were differentially irradiated before compaction.
On the other hand, in some aubrites (Mt. Egerton, Shallowater, Pena Blanca Spring, Norton County) neutron capture effects may entirely be due to space irradiation.
The contrast between the internal and the external is obvious, but not as dramatic as with most other stone meteorites.
Bursting like flower buds, the radiating enstitite crystals in this enstatite rich matrix make viewing this stone one for the more seasoned meteorite enthusiasts given its subtle features and fragile innards.
Pesyanoe is one of the specimens in my collection upon which I hold very fond memories of its acquisition. But like many other pieces, I was unable to share the true enjoyment of Pesyanoe ownership until recently when another similar sized and looking sample of Pesyanoe joined a private American collection. But details on that stone are the prerogative of its owner.
Until next time….
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