Meteor that blasted millions of trees in Siberia only 'grazed' Earth, new research says

A mysterious blast in 1908, thought to have been caused by a meteor, flattened a Siberian taiga forest. This photo was taken in 1938, during an expedition by Russian mineralogist Leonid Kulik, investigating the event.

(Image credit: Sovfoto/Universal Images Group via Getty Images)

A new explanation for a massive blast over a remote Siberian forest in 1908 is even stranger than the mysterious incident itself.

Known as the Tunguska event, the blast flattened more than 80 million trees in seconds, over an area spanning nearly 800 square miles (2,000 square kilometers) — but left no crater. A meteor that exploded before hitting the ground was thought by many to be the culprit. However, a comet or asteroid would likely have left behind rocky fragments after blowing up, and no "smoking gun" remnants of a cosmic visitor have ever been found.

Following the bright light, which lasted for about 1 minute, was an explosion that smashed windows and knocked people off their feet in a town more than 35 miles (60 km) away, the BBC reported. "The sky was split in two, and high above the forest the whole northern part of the sky appeared covered with fire," another witness said in a testimonial. Energy released by the blast was later estimated by scientists to be 185 times greater than that of the atomic bomb dropped on Hiroshima in 1945, according to NASA.

Initial explanations for the blast included volcanic eruptions and mining accidents, according to NASA, but those claims were not supported by physical evidence. Other later suggestions were more far-fetched, such as a crashed UFO or a black hole collision with Earth — a study describing the black hole hypothesis was published in the journal Nature in 1973 (and was soundly debunked in another Nature study published just a few months later).

The most widely accepted scientific explanation is that a rocky asteroid or comet entered Earth's atmosphere and then disintegrated with a bang about 3 to 6 miles (5 to 10 km) above the ground, Pariev told Live Science in an email. But such an explosion should have strewn the ground with rocky debris, which no one has ever found. By comparison, a meteor that exploded over Chelyabinsk, Russia, in February 2013 broke into fragments that were discovered within a week, Pariev said.

The researchers estimated that the Tunguska meteor likely measured between 328 and 656 feet (100 and 200 m) in diameter, and hurtled through Earth's atmosphere at roughly 45,000 mph (72,000 km/h). During its fiery passage, the meteor would lose some of its mass. But iron shed by a meteor traveling at such speeds would have escaped as gas and plasma, oxidized in the atmosphere and then dispersed on the ground, becoming nearly indistinguishable from terrestrial iron oxides, according to the study.

In the case of the Tunguska meteor, the iron-rich space object could have entered Earth's atmosphere at a very shallow angle — about 9 to 12 degrees tangential to the surface. It then would have grazed through the atmosphere, creating a shock wave at an altitude of around 6 to 10 miles (10 to 15 km) above the ground, capable of flattening trees for hundreds of kilometers and scorching the surface. But because of the meteor's mass and momentum, it didn't break up; it then exited the atmosphere and returned to space, the researchers reported.

What's more, the pattern of felled trees at the site is radial — emanating from a single point of tremendous energy release, he said. That's something you'd expect to see after an explosion rather than a sonic boom, "even if it had been strong enough to blow trees over." Boslough added that eyewitness accounts at the time of the incident "are consistent with an object that was descending toward the surface before it exploded."

Mindy Weisberger is a science journalist and author of "Rise of the Zombie Bugs: The Surprising Science of Parasitic Mind-Control" (Hopkins Press). She formerly edited for Scholastic and was a channel editor and senior writer for Live Science. She has reported on general science, covering climate change, paleontology, biology and space. Mindy studied film at Columbia University; prior to LS, she produced, wrote and directed media for the American Museum of Natural History in NYC. Her videos about dinosaurs, astrophysics, biodiversity and evolution appear in museums and science centers worldwide, earning awards such as the CINE Golden Eagle and the Communicator Award of Excellence. Her writing has also appeared in Scientific American, The Washington Post, How It Works Magazine and CNN.