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edit People are Idiots, Numbers are Big
Just briefly, and work with me here, I would like to talk about asteroids and comets. Here we go:
Asteroids and comets are space-born chunks of minerals and ice, rotating about various stellar bodies at various distances. Smaller than planets, indeed too small to even make themselves spherical, asteroids nonetheless pursue roughly circular orbits about stars. Comets are only a touch large, but move rather more quickly, because they move in largely elliptical orbits about a star when they are pulled from their position on the outmost edge of a stellar system, beyond most planets.
Here I will admit that our own solar system does, indeed, contain both asteroids and comets. The asteroids rotate the sun at a distance roughly halfway between Mars' and Jupiter's relative distances from the sun. The comets are in a large cloud, known as the Oort Cloud, further out than Pluto and Neptune, the hindmost planets in our system, discounting the fabled Planet X which still has managed to escape being named.
Occasionally one or the other of the two types of sub-planetary bodies will see fit to careen about our solar system, occasionally hitting one of the nine planets or their moons. The pock-marked appearance of the moon and various other planets and their moons leads us to this conclusion: they are basically museums of every past hit they have had, because their lack of even a thin atmosphere means that they have no defense against smaller hits, and no erosion patterns to remove the craters the impacts cause.
Earth is not left out from this shooting gallery, not at all. But our atmosphere does create sufficient friction to most incoming ballistic objects that they simply burn up, victims of their own speed. We hardly notice them if that does happen, or, if we do, we make wishes on them.
It is the larger meteoric impacts I wish to speak of, however; this past bit was just background, so that we can agree on a common ground.
In the past, Earth has been subject to larger meteoric impacts, rocks hitting us that are too large to be stopped by the atmosphere, bundles of such incredibly excess kinetic energy that they have an extremely noticeable affect on the Earth, and the organisms living upon it. Any meteor larger than about half a kilometer across hits with force to throw billions of tons of dirt and dust into the air.
This dust itself moves with such speed, both on moving upward and on returning to the Earth's atmosphere later, on the other side of the planet, that it can raise the temperature of the air far in excess of 200 degrees Celsius. Plants burst into flame with a temperature change such as that; spontaneous combustion leading to horrific wildfires the likes of which no human alive has ever witnessed. Species die, plants wither, the planet itself falls into a dark cloud of lifeless darkness.
But this doesn't happen often.
Once every 600 thousand years, on average. And far more frequently, such a meteor will just miss. Because the universe is a big place. This has been covered many, many times. Humanity is so incredibly small compared to almost anything else in the universe; we just can't understand that. And our attempts to do so often end badly, because we're just not built for it.
And here we come to what I really want to talk about:
Recently a ballistic object, name irrelevent, passed by the Earth. It was more than 500m across, and would have done significant damage. Had it hit.
People were very worried for a bit there, not because we thought that it was going to hit us (we knew it wasn't), but because our governments had done nothing to prevent a future collision, one which might cause the human race's extinction. They cited astronomical distances, saying that the meteor had come within 400,000 kilometers of our beloved planet and that in astronomical terms, a mouse would starve on the difference between that and a direct hit.
The Earth is a rough sphere, about 6370 kilometers across. The meteor was 600m across. If the earth was only a meter across, the asteroid would have been as big as a pinhead, or much smaller. I don't feel like doing the math. What happened, in other words, was a pinhead came within about a half-mile of our beloved beachball. What this means is that the chances of that pinhead hitting the Earth are so incredibly, irrelevantly, absurdly low that we shouldn't give a shit. If the meteor was "the size of Texas", or there were millions of them, maybe we should be worried. The fact of the matter, though, is that it wasn't, and there aren't, and it didn't come anywhere near us. In layman's terms: while the solar system makes the distance between us and that meteor seem small, it makes the Earth seem even smaller, by a couple orders of magnitude.
I'm not worried.
So please, if you like you can dick around with distance, and science, and philosophy, and the media, but if you don't understand probability, leave it alone. There's a goddamn reason this sort of thing only happens once every few hundred millenia. It's because it's not likely. And the chances that you or I will see an extinction-level, or even just local extinction-level, event are pretty damn low. Except for nuclear war; only 7 minutes to midnight, if you know what I mean.
Here's some easy references:
Apophis being a recent near earth object, and the other two being danger scales.