Since the Chelyabinsk event in early 2013, when a brilliant meteor fireball streaked across Russian skies and exploded with the energy of thirty Hiroshima bombs, humans have paid slightly more attention to the potential danger of asteroids than before. A combination of media attention and the viral spread of eyewitness videos and photos perhaps did more for the cause of Earth asteroid protection than anything else in recent history.
Later analyses that included data from a global infrasound network, designed to help monitor nuclear test-ban treaty rules on bomb detonation, have indicated that the last few decades may in fact represent a slight uptick in asteroid impacts on the Earth. The cause? The probable disruption a million years ago of parts of a mile-and-a-half sized body known as 1999 NC43.
Now the B612 Foundation - an organization devoted to the monitoring and mitigation of harmful asteroid impacts on Earth - has assembled a great visual of the last 13 years of asteroid hits with kiloton or greater explosive energy. Picked up by the infrasound network, the majority of these 26 events were 'airbursts', and most took place over the oceans or relatively remote areas. You can watch the animation below.
Its a sobering reminder of our rather precarious situation in a dynamic and still evolving planetary system, where even our homeworld has, in some sense, not finished assembling itself from the fossil remains of our proto-stellar nebula.
Towards the end of this video is a hint of the B612 Foundation's privately funded 'Sentinel' space mission - an infrared telescope that would scour local space for objects as small as about 30 meters across, and spot 90% of objects larger than 140 meters. These are 'near-Earth objects' or NEOs (objects whose orbits carry them between approximately 1.3 and 0.98 astronomical units from the Sun), the asteroids whose paths have the potential to intersect the Earth's.
Although there's been a lot of talk over the years about spotting and deflecting Earth-hazardous asteroids, there's yet to be a real breakthrough moment. B612's Sentinel mission would be a terrific step to take. Right now the best data we have on NEOs is only for the big guys. It's estimated that we've spotted about 93% of the NEOs larger than 1 kilometer across. Sounds good, right? The problem is that this still leaves an estimated 70 or so unseen, lumbering, kilometer-sized mountains that could pose an enormous threat to our civilization. And that's the big, relatively easy to spot stuff. Push into the regime of bodies that are hundreds to tens of meters across and there must be tens of thousands of NEOs that we simply haven't spotted yet.
The Chelyabinsk meteor was no more than about 20 meters across, yet it exploded with over 400 kilotons of energy. Fortunately this was at seventy-six thousand feet above ground level, mitigating the effect. Still, over a thousand people in a modestly populated region were injured.
And the sobering fact is that it is only a matter of time before something far worse happens.