The Chelyabinsk meteor that exploded over Russia smashed through Earth’s atmosphere on the rebound from a collision with another asteroid in space.
Researchers from Tohoku University in Japan have analysed the debris left behind by the space rock, which caused the second largest asteroid airburst in human history, in an effort to help understand how near-Earth objects (NEOs) could end up on a crash course for our home world.
The scientists found that the rocks left behind by the Chelyabinsk asteroid contained the high-pressure mineral jadeite, which is only formed under extreme pressure and high temperatures. The jadeite was formed under pressures of at least three to 12 gigapascals during a shock that was longer than 70 milliseconds, according to their study.
Using that data, the team were able to figure out that the Chelyabinsk asteroid had to have been smashed off its parent rock by a collision with a much larger space rock – at least 150 metres wide – at a relative speed of around 4,800 kilometres per hour.
null “This impact might have separated the Chelyabinsk asteroid from its parent body and delivered it to the Earth,” said lead researcher Shin Ozawa in the Scientific Reports paper.
If the Earth is ever hit by a larger NEO, it’s likely to be because it was knocked off its usual course, whether by colliding with another space rock or with the gravitational forces caused by another celestial body.
The planet was lucky with the 20m-wide Chelyabinsk asteroid because it was incinerated by the Earth’s atmosphere, leaving just fragments of meteorite to rain down on the town in Siberia in February last year.
Barrelling through the atmosphere at speeds of around 67,000 km/h heated up the asteroid until it exploded, around 30km short of the ground. However, that explosion was still enough to cause shockwaves that blew out windows and damaged buildings, injuring over a thousand people in the process.
The meteorites that survived the fall provide a unique sample for scientists because they actually hit the Earth and their trajectory is well-known.
Ozawa and his team believe that the impact speed shown by the minerals in the meteorites make it likely that the asteroid chunk originated in the main asteroid belt. Because jadeite wouldn’t have survived a second impact, the crash that caused the rock to break was probably the last big bump it ever got, which means it likely happened a staggering 290 million years ago.
However, it likely took a further 280 million years for the asteroid to settle into its place in the asteroid belt, after being shuffled around by the gravitational forces of the asteroids around it and the far off force of Jupiter, which causes the rocks in the belt to group together. This shifting around eventually pushed the asteroid into its Earth-crossing orbit around ten million years ago, for the planet’s second-largest airborne explosion.
The only larger airburst explosion in recorded history was also over Russia and has come to be known as the Tunguska event. Although studies differ on the size of the event, it’s clear that a space rock blew up in the sky near the Tunguska river in 1908, just five to ten kilometres from the ground with an energy around a thousand times greater than the atomic bomb that was dropped on Hiroshima. The power of the Chelyabinsk explosion is estimated at between twenty and thirty times the power of the same bomb.