Sikhote-Alin Meteorites

The Sikhote-Alin meteorite fall was a massive impact event that occurred on February 12, 1947, approximately 440 km northeast of Vladivostok, Russia.

Fall

At around 10:30 am on February 12, 1947, eyewitnesses in the Sikhote-Alin Mountains, Primorye, Russia, observed a fireball brighter than the sun that came out of the north and descended at an angle of about 41 degrees. The bright flash and the deafening sound of the fall were observed for three hundred kilometers around the point of impact near the village of Paseka (approximately 440 km northeast of Vladivostok). A smoke train, estimated at 32 km long, remained in the sky for several hours. As the meteorite entered the atmosphere, traveling at a speed of about 14 km/s, it began to break apart, and the fragments fell together. At an altitude of about 5.6 km, the largest mass apparently broke up in a violent explosion. The strewn field for this meteorite covered an elliptical area of about 1.3 km. Some of the fragments made craters, the largest of which was about 26 m across and 6 m deep. Fragments of the meteorite were also driven into the surrounding trees.

Description

Specimens of the Sikhote-Alin Meteorite are basically of two types;

1. Individuals

Individuals are meteorite specimens showing fusion crust and signs of ablation. These first probably broke off of the main object early in the descent. These pieces are characterized by regmaglypts (cavities resembling thumb prints) in the surface of each specimen.

(Ablation is defined as the removal of material from the surface of an object by vaporization, chipping, or other erosive processes. The term occurs in space physics associated with atmospheric reentry)

2. Shrapnel

Shrapnels are meteorite specimens showing evidence of violent fragmentation. The second type is fragments which were either torn apart in the atmosphere during the descent or blasted apart upon impact. Most were probably the result of the explosion at 5.6 km altitude.

Size

Sikhote-Alin is a massive fall. The overall size has been estimated at just under 900,000 kg. A large specimen is on display in Moscow, and a great number of smaller specimens have made their way into private collections.

Structure and chemical composition

The Sikhote-Alin meteorite is classified as a coarse octahedrite type IIB. It is composed of approximately 93% iron, 5.9% nickel, 0.42% cobalt, 0.46% phosphorus, and 0.28% sulfur, with trace amounts of germanium and iridium. Minerals present include taenite, plessite, rhabites, troilite, chromite, kamacite, and schreibersite. Sikhote-Alin displays a beautiful pattern of Widmanstatten lines when sliced and etched. It is the amount of nickel relative to the amount of iron present that creates this crystalline pattern. This pattern is only present in etched meteorites and is one way of determining the authenticity of a suspected meteorite find.

Iron meteorites are extremely rare. Of all of the meteorites that fall on the earth, scientists estimate that only about five percent are Iron Meteorites.