SIKHOTE-ALIN

"The Sikhote-Alin meteorite shower belongs to the class of unique natural phenomena. It represents the most abundant iron meteorite shower, far exceeding all known meteorite showers both in the number of individual specimens and in their total mass.".

The fall of the Sikhote-Alin meteorite on February 12, 1947, 10:38, Iman city, Primorsky Krai. Drawing by artist P.I. Medvedev, an eyewitness to the event.

"... On 12 February, residents of the taiga region of Krasnoarmeysky District witnessed a very rare phenomenon. At 10 AM, a giant glowing meteoroid was observed moving at enormous speed in the direction of the Sikhote-Alin Ridge. The fall was accompanied by a thunderous noise, producing airshocks that shattered windows, damaged pipes, and caused trees to sway violently as in a strong storm. In some locations, huge oaks and cedars were uprooted. The meteoroid left a dense brownish red smoke trail that remained suspended in the air for an extended period. Explosions were heard. The exact fall location could not initially be determined...."

One of the craters formed by the fall of the Sikhote-Alin meteorite. Painting by artist N.A. Kravchenko (1948).

On the ground at the fall site, many trees were uprooted along with their roots. Surviving trees stood with broken tops and crowns. Debris of trunks, branches, and pine and fir needles were scattered across the crater field. Amid this chaos, craters and depressions were observed. E. L. Krinov, 1981

Initial ground searches failed to locate the impact site. On 14 February, the fall site was accidentally spotted from the air by pilots P.Y. Fartsikov and A.I. Ageev, who were conducting a scheduled flight from Ulunga to Khabarovsk. After arriving in Khabarovsk, they reported their observations to the Geological Administration, which immediately organized an expedition for preliminary exploration of the fall site. The expedition consisted of geologists V.A. Yarmolyuk, G.T. Tatarinov, and V.V. Onikhimovsky. On 21 February the expedition departed from Khabarovsk, and on 24 February, after a difficult two day march through the taiga, the geologists reached the fall site. An hour later, the impact site was reached by Vladivostok geologist F.K. Shipulin with two local hunters, who had undertaken an independent search guided by eyewitness accounts of the bolide's flight direction.

The first to reach the impact site were the Far Eastern geologists F.K. Shipulin, G.T. Tatarinov, V.A. Yarmolyuk, and V.V. Onikhimovsky (from left to right), who investigated the crater pits and discovered the first fragments of meteoric iron. Late February 1947.

The caravan of the first expedition of the Committee on Meteorites en route to the Sikhote-Alin meteorite impact site. April 1947.

At the impact site, the taiga was devastated. Many trees were shattered, their tops cut off. Fragments of tree trunks hung in the crowns of surviving trees. The snow was compacted, and the resulting firm crust easily supported a person's weight. Amidst this chaos gaped craters and pits. The largest crater had a diameter of 26 m and a depth of 6 m. Huge cedars, uprooted, lay radially around the craters. The geologists discovered about 30 craters and pits and mapped their locations. In one of the pits, amidst shattered rock, they collected meteorite fragments.

The Committee on Meteorites was aware of the event from press reports. Later, telegrams arrived from geologist F.K. Shipulin, the Krasnoarmeysky District Committee of the CPSU, and the Far Eastern Geological Survey. A special expedition was dispatched to the impact area, which reached the work site by the end of April. The expedition was led by Academician V.G. Fesenkov. To assist the expedition, a sapper unit was allocated by the Primorsky Military District. The expedition conducted a detailed survey of the impact site, interviewed eyewitnesses, performed a theodolite survey of the area, and collected several tons of individual specimens and fragments of the meteorite shower. However, the main point is that this expedition initiated the subsequent multi-year studies of the Sikhote-Alin fall, which continue to this day.

Sappers extracting the largest fragment of the Sikhote-Alin meteorite, weighing 1745 kg, from a crater pit. Photograph from 1950.

Another large fragment of meteoric iron extracted from a crater pit by the efforts of the sapper unit. Photograph from 1950.

The organizer and leader of these studies was Evgeny Leonidovich Krinov. In the course of this work, the following was established:

Схема дробления метеорного тела во время движения в земной атмосфере с космической скоростью (Кликни чтобы увеличить).

A cosmic body several meters in diameter and weighing hundreds of tons entered the Earth's atmosphere. During its passage, it underwent multiple fragmentation events. The first breakup of the body occurred at an altitude of about 25 km, the last at approximately 6 km.

This fragment formed during the initial stages of fragmentation high above the Earth's surface and almost did not change its orientation during further atmospheric flight. As a result of atmospheric processing, it acquired a shape resembling a projectile's warhead.

Under intense rotation in the atmosphere, fragments from the first stages of fragmentation become rounded and possess a well-defined fusion crust and regmaglypt relief.

Pieces from the first stages of fragmentation traveled the longest path through the atmosphere, during which their surface experienced intense heating. Melting and ablation led to a well-formed crust and a wavelike relief on the meteorite surfaces.

Fragments of the second stage of fragmentation separated from the meteoroid at a lower altitude. They possess regmaglypt relief and a fusion crust, i.e., they still undergo significant atmospheric processing, but retain a fragmental form resulting from the atmospheric destruction of the meteoroid body.

Fragments of the second stage of fragmentation have a finer and sharper relief.

Fragments formed near the Earth's surface during the final stages of fragmentation bear no noticeable traces of atmospheric processing and retain the fragmental form arising from the atmospheric destruction of the meteoritic body. They are often devoid of fusion crust and regmaglypt relief. Such fragments readily become coated with a layer of rust.

Finally, pieces from the third stage replicate the shape of parts of the internal structure of the meteoritic material.

Fragments of the Sikhote-Alin meteorite.

Over an area of about 20 km² more than 100,000 fragments fell, with masses ranging from fractions of a gram to hundreds and even thousands of kilograms.

The wondrous world of the Sikhote-Alin meteorite fragments is a vivid illustration of the effectiveness of the mechanical destruction of cosmic bodies during deceleration in the Earth's atmosphere.

Large pieces formed craters on the soil surface (from 0.5 to 30 m in diameter).

Their impacts were so powerful that these pieces were partially destroyed, and their fragments were ejected from the craters.

In total, several tens of thousands of fragments were collected, with a total mass exceeding 27 tons. The largest intact specimen weighs 1745 kg. The Sikhote-Alin meteorite is classified as a coarsest octahedrite of chemical group IIB. Its chemical composition is: Fe 93.29; Ni 5.94; Co 0.38; Cu 0.03; P 0.46; S 0.28 (wt.%).

Cross-section of a Sikhote-Alin meteorite fragment.

The mineral composition is dominated by metallic iron; in minor amounts, troilite (FeS), schreibersite ([Fe,Ni]₃Р), and chromite (FeCr₂O₄) are present. Tensile strength is 4.4 kgf/mm², compressive strength is 40.6 kgf/mm². Orbit calculations showed that the Sikhote-Alin meteoroid, even at its greatest distance from the Sun, remained within the asteroid belt and never approached the Sun closer than the radius of Earth's orbit. The disintegration of the Sikhote-Alin meteorite's parent body, which led to the formation of this orbit, occurred 350 million years ago.