METEORITE IMPACTS

COUNTLESS IMPACTS CONTINUE TO SHAPE EARTH, OTHER PLANETS AND MOONS IN OUR DYNAMIC SOLAR SYSTEM.

FEBRUARY 12, 1947, 10:30 A.M.: A woodsman stacking logs in the frozen forest of eastern Siberia stopped working when he noticed a sudden flash of light, brighter than the Sun, streaking across the sky. Dozens of others in the area saw the flash too, and they described a huge fireball that exploded, bursting into smaller pieces that fell to Earth with cracking and roaring sounds. A huge, red-tinged column of dark dust hung in the sky for several hours, marking the fireball's path.

An iron meteorite weighing perhaps 100 tons, more than three times as much as Ahnighito—displayed at the center of this hall—had exploded in the dense lower layer of Earth's atmosphere. It shattered into tens of thousands of fragments that crashed into the thick forest, tearing apart and uprooting trees and digging hundreds of craters in the snowy ground.

INTO THE FROZEN FOREST

The Sikhote-Alin meteorite shower fell in a remote forested area of eastern Siberia. Geologists spent two days during the coldest part of the winter searching for the impact site, in an area that is home to Siberian brown bears and Amur tigers. They hacked through miles of dense taiga, a type of evergreen forest found in swampy subpolar regions, before finding the craters.

Expeditions to Sikhote-Alin have gathered more than 29 tons of meteorite fragments, but perhaps twice that amount remains on or under the ground. The twisted shape of the fragment displayed here reveals the intense, wrenching force of the explosion of the original mass. The fingerprint-like impressions in its surface, called regmaglypts, show that friction with the atmosphere started to melt it.

When the Sikhote-Alin fireball appeared in the sky, artist P. I. Medvedev was painting at his easel in the nearby town of Iman. He immediately began to paint the image that was later featured on this Russian stamp, issued in 1957 to commemorate the 10th anniversary of the meteorite shower.

The meteorite mass that formed this crater weighed roughly 1,300 kilograms (2,870 pounds) before it broke apart upon impact. The crater, one of the larger ones at Sikhote-Alin, measures 11 meters (37 feet) across. Uprooted trees and shattered pieces of rock lie strewn around the crater rim.

THE BIGGER THEY COME, THE HARDER THEY FALL

As geologists searched for meteorites by digging beneath craters at Sikhote-Alin, they noticed something peculiar. Many fairly large meteorite samples were buried at the bottom of small craters measuring no more than two meters (6.5 feet) across. Larger craters, on the other hand, usually contained many very small meteorite fragments.

But the researchers knew that larger impacting meteorites must have made the larger craters. These meteorites apparently landed with so much kinetic energy that they shattered into tiny fragments. Smaller impactors were less likely to break apart because they hit with less energy.