Heads up – it’s explosive-meteorite season. A new analysis suggests that powerful incoming meteors like the rock responsible for last year’s explosion over ChelyabinskMovie Camera, Russia, may not be completely random.

Brothers Carlos and Raúl de la Fuente Marcos at Complutense University of Madrid in Spain used data from the infrasound sensors of the Comprehensive Nuclear-Test-Ban Treaty Organization – which were designed to detect nuclear detonations on Earth – to measure 26 explosions from meteors hitting the atmosphere with energy of up to 1 kilotonne of TNT between 2000 and 2014. Seven other events were taken from published literature.

They found that several explosions occurred within a handful of days as similar explosions in previous years. For instance, the Chelyabinsk impact was on 15 February, 2013, while a meteorite over the South China Sea was recorded on 18 February, 2000, at almost the same latitude. The number of meteors in the study is admittedly very small, but a statistical analysis suggests that rather than being random events, there may be a seasonal aspect to explosive meteorites.

A seasonal peak was discernible in the southern hemisphere, where explosions clustered between September and December. In the northern hemisphere, blasts seemed evenly distributed throughout the year, although some individual events appeared to be linked.

Seasonal showers

We already know about seasonal meteor showers caused by debris from comets entering Earth’s atmosphere when the comets cross our planet’s path. But while comets shed centimetre-scale particles to create ordinary meteor showers, explosive impacts may be caused by streams of metre-scale objects. These might be the remnants of large asteroids ripped apart by gravitational encounters with other bodies, like Jupiter, or objects kicked out of the asteroid belt and trapped in orbits that regularly carry them into the vicinity of Earth’s path.

Unfortunately, it is hard to compare the material of meteorites from two potentially linked explosions, as in many cases, no samples are recovered. But the authors hope their work will inspire further examination of existing meteorites.

“Although based on a small sample – lucky for us, these relatively big things are not falling often – our work is intended to spawn multidisciplinary research that may eventually help us all to better deal with this problem,” says Carlos de la Fuente Marcos.

Alan Harris at the Space Science Institute in Boulder, Colorado, is not inspired by the new research. He points out that astronomers would not change their strategy and stop searching the skies during a supposedly low-probability month – and for small, local explosions, advanced knowledge of a significant meteor could actually make the situation worse.

“Evacuations are not harmless,” he says, adding that they typically result in a death rate of about 1 in 100,000 people. While no deaths were attributed to the 2013 explosion over Russia when it came without warning, “emptying out Chelyabinsk might kill 10 or so people. We run a serious risk of overreacting.”

Journal reference: arxiv.org/abs/1409.0452v3
http://www.newscientist.com