On that day, 31 October 2015, a rock about 650 metres across just missed hitting us. It was smaller than the 10km rock that helped wipe out the dinosaurs about 65 million years ago. I know that some of the dinosaurs survived. We call them birds. But the point is that a fast-moving rock 650 metres across would cause a lot of damage – depending on where it landed. The impact site could be a potential super-volcano such as Yellowstone National Park in the USA or Mt. Etna in Italy, or it could be mid-Pacific Ocean. I don’t know which is worse – volcanic eruptions blackening the skies world wide, or massive tsunamis.
Regardless, a rock hitting the Earth at some 30km/sec would cause a lot of damage to the human race.
Now, if the human race had been given three years warning and if the rock (2015 TB145) had been on a direct collision course, we would have had enough time to gently nudge it off course. The radius of the Earth is about 6,400km, so that is the maximum distance that we would have to shift the asteroid by.
But we didn’t have three years warning – we had three weeks! It was discovered on 10 October 2015 and 21 days later zipped past us at a distance of just 486,000 km (1.27 times the distance between the Earth and the Moon, or 1.27 Lunar Distances).
And there are more of these civilisation-busters. Fewer than half of the estimated 2,400 near-Earth asteroids, between 300 and 500 metres across, have been discovered. We spend more money making movies about asteroids hitting the Earth, than we do on looking for these asteroids.
This asteroid, 2015 TB145, was hard to find. It spends most of its time out past Mars and its orbit is highly tilted relative to the plane of the planets (about 40o). As it zipped past at an uncomfortably close distance, we observed it with some very big radio telescopes and found that it was rotating every five hours.
The media (if it did report on this civilisation-killer rock) took the jolly fun angle. The rock was roughly spherical with a few bumps and craters, so it looked a little like a skull. So, because 2015 TB145 passed us on Halloween, the media nicknamed it the “Great Pumpkin” or “Skull Asteroid”.
But I take a slightly more sombre approach. I think that 2015 TB145 is the Universe’s way of asking, “Hey humans, how’s your Space Program going?”.
We humans have to become a space-going race. Avoiding destruction is only one reason. The benefits include all the spin offs that come with every new technology, most of which can’t be predicted. Earth has been our Cradle of Life, but as we grow, we have to leave the cradle.