Four years ago today an explosion shattered the morning sky over the Chelyabinsk region in southwestern Russia, the result of a 60-foot-wide fragment of an asteroid entering Earth’s atmosphere at over 40,000 mph and brilliantly blowing itself to smithereens at 97,000 feet up. Even at that altitude, the resulting flash of light and air blast was powerful enough to cause extensive damage on the ground, shattering windows, knocking in doors, and causing injury to nearly 1,500 people across towns in the area—several of them seriously.

This was the largest observed meteor since the famous 1908 Tunguska event, but thanks to the prevalence today of dashboard and CCTV cameras in Russia this one was well-recorded. (I remember seeing the videos online within an hour after it happened!) The footage has allowed scientists to not only determine the energy of the Chelyabinsk meteor explosion—about 500 kilotons—but also the object’s trajectory and origin.

Watch a video below of footage captured from various locations of the Chelyabinsk meteor:

And here’s another video, focusing on the effects of the shockwave resulting from the air blast:

The Chelyabinsk meteoroid wasn’t discovered before impact because it came from an area of the sky too near the Sun…and, as strong as its explosion was, it was still within a size range that is difficult to spot with current technology. Even though the chances of such an event occurring over a populated area on any given day are extremely small what happened on Feb. 15, 2013 showed us they are certainly not zero. If we are to ever develop a system to identify such objects before they actually impact Earth and either warn all those at risk or alter the objects’ courses, first we need to be able to find them.

This year Asteroid Day is June 30, and researchers are discussing our options and trying to get an action plan assembled and agreed upon. But as of now we are still a long way off from having anything in place.

Chelyabinsk was a wake-up call. Did we hear it? Like Neil deGrasse Tyson likes to say during his presentations, “asteroids are nature’s way of asking ‘how’s that space program coming along?'”

UPDATE 6/30/17: On June 30, 2016 a transcript was posted from a talk with three of the University of Arizona’s asteroid specialists. Tunguska and Chelyabinsk were discussed, as well as Bennu — the subject of NASA’s OSIRIS-REx mission — and in general the chances of a large-scale asteroid impact and what we could do to prevent it. The bottom line: it’s not something we should panic over, but it is good science to study asteroids and learn more about them, regardless. Read the interview here.