The meteor shower that brought Tunguska is due in June
That disastrous rock may now looks to have been a Beta Taurid passenger
- Analysis of the Tunguska tree-fall patters suggests a familiar source for the asteroid that caused it
- Its timing also fits perfectly with a late June annual meteor shower
- Nonetheless, it's more interesting than dangerous. Put down that helmet.
It's just after seven in the morning on June 30, 1908 as a man sits on the front porch of a trading post in Vanavara, Siberia. That is, until a sudden blast of heat at 7:17 hurls him from his seat. It comes from a huge asteroid exploding about 28,000 feet above the Podkamennaya Tunguska River 40 miles away.
Suddenly in the north sky… the sky was split in two, and high above the forest the whole northern part of the sky appeared covered with fire… At that moment there was a bang in the sky and a mighty crash… The crash was followed by a noise like stones falling from the sky, or of guns firing. The earth trembled.
Such asteroids are not that rare — scientists estimate they happen about every 300 years. There was one over the Russian city of Chelyabinsk in 2013, and though smaller at 11,000 tons than the Tunguska rock, it nonetheless injured 1,200 people and caused damage to buildings up to 58 miles away.
It seems like we now know how the Tunguska asteroid got here. Physicist Mark Bosloughof Los Alamos National Laboratory recently presented, at the American Geophysical Union fall meeting, a new analysis of the tree-fall pattern in the Tunguska area. It suggests that the rock may have arrived during the annual Beta Taurid meteor shower. The next one's in June 2019. (There's another Taurid shower each October.) A quote from the presentation: "If the Tunguska object was a member of a Beta Taurid stream … then the last week of June 2019 will be the next occasion with a high probability for Tunguska-like collisions or near misses."
The Tunguska event
The Tugnuska asteroid , a 220-million-pound space rock, is believed to have been traveling at about 33,500 miles per hour, heating the air around it to 44,500° Fahrenheit before it exploded, flattening trees for about 800 square miles. As NASA puts it: "Eighty million trees were on their sides, lying in a radial pattern." The timing for being a Beat Taurid is about right, too, since it arrived in their typical late-June window.
The first scientific investigation occurred 19 years after the event, led by Leonid Kulik of the St. Petersburg Museum. Don Yeomans, of NASA's Near-Earth Object Office describes what Kulik found when he arrived in the area: "At first, the locals were reluctant to tell Kulik about the event. They believed the blast was a visitation by the god Ogdy, who had cursed the area by smashing trees and killing animals." Kulik was able to follow the flattened trees to identify "ground zero. "Those trees," according to Yeomans, "acted as markers, pointing directly away from the blast's epicenter." And eventually, "when the team arrived at ground zero, they found the trees there standing upright — but their limbs and bark had been stripped away. They looked like a forest of telephone poles."
The Taurus' elliptical orbit
The Earth encounters the Taurids twice a year due to the belt's odd orbit, which is roughly on the same plane as ours. We pass through it twice a year, as the belt carries Taurid materials toward the sun in October, and away from the sun in June. It's also a very elliptical orbit that gets as close to the sun as Mercury, but also stretches far beyond Earth's orbit.
The October encounter is visible in our autumn night skies, but the June visit occurs during daylight so it's not as visible. Its passengers are primarily spotted via radar.
Some years we encounter denser regions of the Taurid stream than others, and 2019 is one of those years, with scientists saying we'll be seeing more incoming material than any year since 1976. That year, Apollo-mission seismometers installed on the moon's surface recorded an unusually high number of Taurid impacts.
The odds of another Tunguska blast early this summer
Neither Bosloughof of anyone else predicts a Tunguska-style event in June, but if the new calculations are correct, it's just the meteor shower in which it probably arrived back in 1908. According to physicist Peter Brown, who presented the new analysis with Bosloughof, "This is not something that should be keeping you up at night." Paul Chodas, of the Center for Near Earth Object Studies, says, "There are no objects in our catalogue that have any significant impact probability in the next 100 years."
In fact, if there are any near misses this summer, as Bosloughof says, our best odds of finding out if the Beta Tarids did, in fact, carry any Tunguska-sized asteroids would be to spot them in telescopes them as they streak away through space from a much-relieved Earth.
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