Years ago, we would discuss a potential collision of the Earth with the 2004 MN 4 asteroid – also known as 99942 Apophis – on Friday, 13th of April, 2029. The estimated diameter of this rock was 270 meters. The collision was first delayed to April 13th, 2036, and then it was deemed very unlikely.
This spectacular collision assumes a 500-kilometer asteroid. We're talking about rocks whose linear radii are 2,000 times smaller, so the corresponding mass is about 10 billion times smaller. Don't expect the video above to become a reality anytime soon.
After some time, NASA's Near Earth Object Program finally reports some potential collisions whose Torino scale is nonzero.
These objects are:
- 2011 AG5
- 2007 VK184
The second guy may collide with us on June 8th, 2048. Adjust your itineraries accordingly (and buy assets in Czechia which are mostly safe). The odds of that collision are 1 in 1,800. Other potential dates contribute to the overall odds by less than 1 in 50,000.
While the collisions wouldn't be anything like the video above, they would be devastating for a big region of the Earth.
For example, a 200-meter asteroid in diameter which is just a bit larger than the two candidates above would do pretty interesting things. If it hit the Atlantic ocean, the resulting tsunami would swallow both Great Britain and the entire U.S. East Coast.
So with our candidates whose chances to "succeed" are about 1 in 1,000, we may be talking about some tsunami that destroys one-half of Great Britain and one-half of the U.S. East Coast. While 1 in 600 is "probably not", you can't feel really safe.
My broader point is that there are many risks that are much more imaginable than an Earth that gets fried at 16 °C or that suddenly starts to warm up 10 times faster than in recent decades etc. A collision with an asteroid has calculable odds. They depend on basic laws of mechanics and geometry.
With a strong enough technology and healthy economy, we would be able to deflect such an asteroid. We would probably know that the collision is near certain and the approximate predicted location of the collision a few years in advance and that could be enough to "act". Of course, if the mankind became a pile of hippies who only have access to energy to store their food for hours in their effective fridges, and only when the wind blows, we couldn't act.
If you want a greater asteroid whose diameter is 560 meters, you need to wait for a possible collision through 2182. The odds are 1 in 4,000 right now.