Fun new facts about the Chelyabinsk fireball
But scientists are still furiously investigating the meteoroid that exploded over that city 11 months ago, evidenced by three new papers that come out today in two top journals.
In Nature, a paper authored by a slew of international scientists and led by Canada's own Peter Brown shows that the airburst -- as the detonation of a fireball like Chelyabinsk's is known -- was incredibly powerful.
Their study calculated the peak brightness of the Chelyabinsk airburst to be 30 times greater than the sun. The detonation had the energy equivalent of 500 kilotons of TNT. For reference, estimates of the force of the atomic bomb that exploded over Hiroshima are somewhere in the vicinity of 12 to 20 kilotons of TNT.
The good news: in any 20 year period, there is only a 13 per cent chance that an airburst as powerful as or more powerful than Chelyabinsk will occur.
The sort-of-good news: existing techniques for estimating the damage of an airburst don't synch up with observations. Using math based on the effects of nuclear weapons, as scientists normally do, tends to overestimate the damage.
The bad news: Chelaybinsk still broke a lot of windows, and small bolides like this one -- it was just 19 metres across -- pose a greater risk than previously thought. Scientists have successfully identified most near-Earth asteroids larger than 1 kilometre in diameter. But Brown's analysis shows that the number of impacts (either craters or mid-air explosions) from asteroids with diameters in the tens of metres may be an order of magnitude higher than researchers have calculated using other techniques.
Brown, a professor at Western University in London, Ontario, happens to be the world's top expert at analyzing fireball events with infrasound technology. I wrote a feature a few months ago about what the day of the blast was like for Brown and his wife, professor Margaret Campbell-Brown (spoiler alert: it was crazy. Not least because it indefinitely delayed their Valentine's Day date.) You can read that story here.
A second paper published in Nature today tracked the path of Chelyabinsk using a professional suite of instruments and also using YouTube videos shot by amateurs. Its orbit was similar to another near-Earth asteroid known, jazzily, as near-Earth asteroid 86039 (1999 NC43). The authors of that paper think that one, which has come really close to Earth, and Chelyabinsk were once part of the same object.
Last but not least, a study in Science discovered that the Chelyabinsk meteoroid was 4,452 million years old, that it was an ordinary chondrite, the most common type, and that it went through a "shock event" 115 million years after the creation of the solar system, which resulted in a bunch of veins running through it that helped it blow up sooner rather than later after it entered Earth's atmosphere.
Qing-Zhu Yin, a planetary scientist at University of California Davis who participated in the Science study, called the event a "wake-up call" in statement.
"If humanity does not want to go the way of the dinosaurs, we need to study an event like this in detail."
Kate Allen is the Star's Science and technology reporter. Find her on Twitter at @katecallen.