Celebrate (And Respect) Asteroids Today!

Artist concept of an asteroid passing by Earth. NASA

110 years ago today about 7:17 a.m. local time, an asteroid or comet streaked through the atmosphere and exploded over eastern Siberia near the Stony Tunguska River. Known since as the Tunguska event, the object left no crater. Instead it appears to have disintegrated at an altitude of 3 to 6 miles (5-10 km), creating a shockwave that leveled more than 80 million trees with the energy of a 15 megaton atomic bomb.

The blue-white meteor shown brighter than the sun. Eyewitness S. Semenov, who lived 40 miles (65 km) south of the explosion, reported seeing it for 10 minutes and feeling the heat of the fireball so intensely he wanted to rip off his shirt. Many reported loud booms resembling thunderclaps or cannon-fire.

Photograph of fallen trees from Leonid Kulik’s 1929 expedition taken near the Hushmo River. Kulik Expedition

Remarkably, no one was killed in the blast which extended in a butterfly pattern 43 miles long by 34 miles wide. Because the region was so remote, it wasn’t until 1927 that an expedition led by Russian mineralogist Leonid Kulik arrived for a scientific study and a search for an impact crater and possible meteorites. Neither was found.

The sample of a “surviving” tree shown here was cut during the first scientific Tunguska expedition in 1927, probably by the Leonid Kulik himself. It shows some burn marks (red arrow), as well as a changed (faster) growth of the tree after the event. Herbert Raab

Later expeditions did careful analyses of the soil and trees and discovered small magnetite and silicate spheres as well as enhancements of iridium, an element common in meteorites. Debate goes back and forth whether it was a comet or asteroid fragment that disintegrated that day. Comets are fragile and break apart easily, the reason to consider one as the cause, but the same is true of some types of asteroid material.

Downed trees pointing away from the epicenter of the aerial Tunguska explosion. Leonid Kulik

Some carbonaceous (car-bun-AY-shuss) chondrites — dark, carbon-rich stony meteorites — will crumble between your fingers if you’re not careful. That fact combined with the composition of the spheres and taking into account that not a single meteorite of more than 40,000 known has been definitively linked to a comet makes me think that the Tunguska impactor was an asteroid.

Depending on composition, a small asteroid (meteoroid) can lose up to 99% of its mass during its passage through the atmosphere traveling at typical speeds of 50,000 mph. Good thing Tunguska happened over a thinly populated area. Had it occurred over a metropolitan region, massive devastation and loss of life would have resulted.

Check out asteroid programs all day today and tomorrow on youtube. Click the image to go there.

Tunguska is the largest impact event in recorded history, and something similar is guaranteed to happen again. That’s why we’re celebrating Asteroid Day, an annual event begun in 2015 on the June 30 Tunguska anniversary. Various events are held on Asteroid Day and range from lectures and educational programs to live concerts and broader community events all to raise public awareness of the need for increased detection and tracking of asteroids.

Asteroid 162173 Ryugu photographed Japanese Hayabusa2 spacecraft on June 26. The picture was taken at a distance of just 12 miles (20 km). Ryugu is about a half-mile (0.9 km) across. JAXA

There are a handful of special events in the U.S. and many in Europe including a star party at Yerkes Observatory in southern Wisconsin and a chance to talk with experts and handle meteorites at the Perot Museum of Nature and Science in Dallas, TX. Click here for more. Or you can just drop in on the 48-hour-long TV broadcast on youtube and listen to asteroid experts asteroids discuss cool topics like the best ways to mitigate potential dangerous impacts (slam a spacecraft into an asteroid) and upcoming asteroid flybys.