One of my fondest memories of my childhood is watching “B
movies” on Saturday afternoons with my mom while my dad was still at work. There were the classic vampire, werewolf and
ghost stories, but one of my favorites was the 1951 science fiction classic “When
Worlds Collide” about (as the title suggests) a collision between the Earth and
another planetary body that will destroy both. Unlike the modern incarnations of “Armageddon”
and “Deep Impact”, there is no rush to destroy/deflect the incoming body, but
there is a last ditch attempt to build an “ark” and evacuate a few and re-start
civilization on a (conveniently) trailing (conveniently) Earthlike planet. For the 50s, it was way ahead of its time.
Fast forward to the early 1990s and like a good, young
scientist I’m catching up on the literature and while I’m reading Nature one day, I noticed an article entitled “Impacts on the Earth by asteroids and comets:
assessing the hazard” – it started off with the cheerful sentence:
There is a 1-in-10,000 chance that a large (2-km diameter)
asteroid or comet will collide with the Earth during the next century,
disrupting the ecosphere and killing a large fraction of the world's
Now I knew that an asteroid impact was the big theory (really
only a few years old at the time) that had wiped out dinosaurs 65 million years
ago. But the paper went on to explain
that things hit the Earth all the time and that – as you might imagine – the
frequency of the event and size of the object are inversely proportional – little things hit all the time
(and burn up in the atmosphere) – while the impacts of larger objects are
exceedingly rare – but not as rare as I thought!
I started digging through the literature and find out that comets and pretty
large asteroids– termed Near Earth Objects, or NEOs, capable of
producing H-bomb like explosions “get close” fairly often and that we usually
don’t notice them until they’re right on top of us.
So, it was with that weird combination of fascination and
paranoia that I saw a report the other day that on Monday asteroid 2009DD45 passed
within 45,000 miles of the Earth. 2009DD45
was about 100m in diameter and was capable of producing a “nuclear bomb” level
explosion similar to that of the famous Tunguska event that flattened a big
chunk of Siberia in 1908. For those keeping score, 45,000 miles puts you
outside of satellites’ but well inside the Moon’s orbit. The best part – it was first observed only two days
Not much time to build an ark. Happy Friday!