The Statistics of Large Space Rocks

Jupiter was recently hit by a giant space rock and astronomer @jose.luis_pereira (Instagram) was lucky enough to capture the impact in this incredible footage.

Encounters like this always remind me of our relative fragility on planet Earth. Although Jupiter’s gravity protects us from more frequent large impacts, there’s an inevitability when it comes to future encounters with big space rocks. You need only glance up at the Moon for clear evidence of this destructive heritage.

The statistics of space rock encounters are both reassuring (in terms of long timescales) but also gravely concerning (in terms of raw destructive power).

On average, every few hundred years, the Earth is hit by an object some 30-60 meters in diameter. Such an impact generates enough energy to devastate an entire city if the final shockwave is concentrated in the right position and direction. The 2013 Chelyabinsk and 1908 Tunguska events are recent example of such encounters.

Then every 10,000 years we’re hit by a 200-500 meter wide object, large enough to trigger short term but significant climate changes, potentially lowering global temperatures and disrupting crop growth and finely balanced ecological systems.

Then every million years a 2-4 kilometer wide impact can occur, releasing energy equivalent to the explosive output of every nuclear weapon on the planet!

Finally on a hundred million year timescale Earth can be visited by something like the Chicxulub event that wiped out the dinosaurs, an object some 10-20 kilometres across. That’s enough destructive power to wipe out vast swathes of life across the entire planet.

As a species we’re only a few million years old and our recorded history takes us back a paltry 10,000 years. It makes you wonder therefore, what unrecorded and long forgotten destructive encounters our distant ancestors experienced and survived? Or is our species yet to be challenged by any of the bigger impacts mentioned above?