Who's been taking potshots at Earth? A new study shows how a 200-metre-wide cluster of rocks, first spotted by scientists in 2011, could have spawned the Chelyabinsk meteor which exploded over Russia earlier this year.

If correct, that means we may need to watch out for further impacts from other fragments of the cluster, which are still at large, in orbit around the sun.

The meteor that exploded over Russia on 15 February, scattering debris across the Chelyabinsk region and injuring hundreds , came as a complete surprise. Since then researchers have traced it to the Apollo asteroid family, but no one had matched it to a particular member of the group.

Now Carlos de la Fuente Marcos and his brother Raul, both of the Complutense University of Madrid, Spain, are pointing the finger at asteroid 2011 EO40. Roughly 200 metres wide, it is a rock – or cluster of rocks – previously listed as potentially hazardous by the International Astronomical Union's Minor Planet Center in Cambridge, Massachusetts.

Rubble pile

First the pair used a computer simulation to create hypothetical orbital paths around the sun that would have intersected with Earth at the time that the meteor hit. Then they searched a database of known asteroids for ones that could have produced rocks that follow those orbits . The closest match was with 2011 EO40.

Most asteroids aren't solid rocks but rather rock clusters that have been gradually fragmenting for eons. "Most asteroids are rubble piles, very fragile," says Carlos. So the brothers also simulated the disintegration of an object the size of 2011 EO40 and showed that it could fragment to produce a Chelyabinsk-size object that would impact with Earth at the correct time.

Future observations of 2011 EO40 could help confirm it as the Chelyabinsk parent. Analysing the light bouncing off it would let us match its composition to fragments of the meteorite collected in Russia. Sending a probe to bring back samples of the asteroid is the only way to be sure, but that is a hugely expensive mission that is unlikely to happen. "The cheap but not fully conclusive approach will have to suffice for the time being," says Carlos.

Asteroid census

If 2011 EO40 really is Chelyabinsk's parent, future observations should also help us predict if Chelyabinsk has any siblings still in orbit that might also pose a threat to Earth, says Carlos. "Having a precise census of this population can help us predict similar impacts in the future."

Jorge Zuluaga of the University of Antioquia in Colombia, who traced the Chelyabinsk meteor to the Apollo asteroid family, cautions that EO40 2011 has yet to be confirmed as the parent. And even it is, he is not too worried about it spawning further impacts.

"I don't think this particular asteroid is more hazardous than others in the MPC list," he says. He also points out that the asteroid itself isn't on a direct collision course with Earth, in any case.

Meanwhile, other researchers are working to piece together the orbit of the Chelyabinsk meteor by different methods. One recent study by Simon Proud of the University of Copenhagen, Denmark, unearthed satellite pictures that show what the meteor looked like from space as it streaked through our atmosphere.

Quelle: NewScientist