The chunk of space rock that streaked across a Siberian sky in February 2013 left its mark via tweets and viral videos shared around the world. But the fireball's greatest legacy may be the insight it offers into the longevity of Near Earth Objects (NEOs) still out there. Researchers analyzing several fragments of the Chelyabinsk meteorite — named for the Russian city over which it exploded — found evidence of a significant impact event prior to the rock's entry into Earth's atmosphere. Based on the fragments' composition and, in particular, the specific shape and distribution of jadeite crystals, the team determined that the parent body of the Chelyabinsk meteorite collided with another asteroid that was at least 500 feet (150 meters) in diameter.
Birth of a Bruiser
The team based their theory on shock-melt veins found in the fragments which contained needle-like crystals of jadeite. The mineral jadeite forms under high pressure, such as during an impact event. From the shape and location of the jadeite and other minerals, researchers determined that the Chelyabinsk parent asteroid collided with the second asteroid at a speed of at least 3,400 miles per hour. That collision, say researchers, likely caused the 30-60 foot chunk of rock that would become the Chelyabinsk meteor to break off from its parent body. The team estimated the massive collision happened up to 290 million years ago. That's a particularly hefty span of time, given that the average "lifetime" of a space rock in our solar system's asteroid belt has been calculated to be less than 10 million years. While more research is needed, the proposed timeline suggests that asteroids — including NEOs that pose a potential threat to Earth — may have much greater longevity than previously estimated. The analysis is published today in Scientific Reports.
The new study clarifies previous research on Chelyabinsk fragments by a different team. Those researchers had identified anomalies, including a fusion crust, which suggested the rock had been melted and cooled at least once before. That team theorized the meteorite had been involved in an earlier collision, or had traveled too close to the sun. The current study, then, puts this question to rest. The Chelyabinsk fireball's explosion was the second largest airburst recorded on Earth — and an impressive example of the destructive force NEOs can bring to our planet.