Sixty six million years ago - the end of the Cretaceous period - an asteroid or comet struck the Earth near what is now Chicxulub, Mexico creating a crater 150 kilometers in diameter. Huge tsunamis that rose hundreds of feet as they approached coastlines. Worse, firestorms swept the planet and the oceans underwent a sudden and deep acidification. Food chains collapsed on land and in the oceans and with them three quarters of plant and animal species vanished.
Arguably it was a bad day.
If the non-avian dinosaurs only had evolved larger brains perhaps they would have made it to the point where they had good astronomy and a good enough space program. But nature keeps moving on and the massive change allowed other lifeforms to evolve including us. In retrospect it was a great day for the human race.
Could it happen again? That one's easy - 100 percent probability. Fortunately we're at the point where we have astronomy and a space program so it makes sense to think about risk and mitigation efforts.
In 1994 a comet called Shoemaker-Levy 9 broke into 21 major pieces and struck Jupiter. It had been captured by Jupiter's gravity and had been orbiting the planet for about three decades it put on a show that would have devastated life on Earth.
An Earth strike would be different and Jupiter's large size makes it a more likely target it did ring alarms and people started thinking about the probability of something big enough to do serious damage hitting the Earth as well as what could be done about it. After all - we had telescopes to figure out likelihoods and rockets to do something about it.
On the 1st of July, 1770 we came very close to a major extinction event - one that probably would have included humanity among the erased. Lexell's comet came with six times the distance between the Earth and the Moon. Cosmically speaking that's a near miss. New comets tend to appear anywhere between a few months to a year before they could be dangerous. But there's much more than just comets out there.
NEOs - Near Earth Objects - are comets or asteroids that come close to or pass through Earth's orbit. They range in size from a few meters to several kilometers. Small ones are common and tend to fragment or disintegrate leaving only small pieces for collectors and scientists. Moving up the size scale you pass through city killers to objects capable of global devastation. Fortunately the big ones are fairly easy to spot, but over ninety percent of the estimated city killers have yet to be cataloged.
A program to funding the construction and operation of new survey telescopes along with retrofitting existing observatories was kicked off about ten years ago with the US and EU taking part. It's relatively inexpensive and has made some progress, but the Trump Administration cut funding.
So what can you do? With enough advance warning you can evacuate regions for objects in the city killer size range. Moving up the size scale means using rockets to intercept the threatening NEO. What to do with it is non-trivial and depends a lot on its composition and size. That's an interesting subject for a future post if there's interest (hint: you probably don't want to nuke it) , but an important step would be expanding missions to asteroids of various sizes to learn about their makeup. In addition to insurance there are technical and scientific benefits that are probably justification enough.
Perhaps it would help us think about preparation and mitigation - the next pandemic and global warming will both make their presence known with much higher probabilities in the next few decades.
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