OTHER SPACE TOPICS
- topics that don't fit into the other categories -

We've been hit before...and it's just a matter of time before it happens again.

And so, defending Earth against killer asteroids is a legitimate objective of space development. Yet, just how great is that risk given our modern ability to detect and react to such a threat?

OUR CURRENT KNOWLEDGE
Modern telescopes have become much, much better at detecting asteroids. The following animation demonstrates just how rapidly we are now detecting new asteroids. Not only are we able to detect more and more asteroids but we are also able to detect smaller and smaller asteroids. That's comforting news because, if there's a killer asteroid out there with our name on it, being able to detect it years or even decades into the future will give us the opportunity to deflect it or, if not, at least evacuate the impact area. But despite the tens of thousands of asteroids that we've detected, none reach a high level of concern for impact.

THE SIZE OF UNDETECTED ASTEROIDS
Bigger asteroids are more easily detected than smaller ones -- this is obvious. Fortunately, we can actually estimate the number of remaining asteroids of any given size that remain undetected. When one is first able to detect asteroids down to a given size, a lot of such asteroids are detected in rapid order. The remaining undetected asteroids start to decrease. As this happens, the rate of discovering new asteroids of that size starts to decrease. One can mathematically use that detection rate to estimate the total population of asteroids of that size.

The good news is that there comes a point in which the detection rate of large asteroids decreases to the point where we calculate that it is more likely that not that there is no more remaining asteroids to be detected of that size. Currently, that point is somewhere around two or three kilometers in size. This is very good news since we are getting to the point where there are no more undetected asteroids capable of having global impacts (e.g. putting the human species at risk of extinction).

The other good news is that, even if we were to detect a very large asteroid that will eventually hit Earth, it is far more likely that not that such as asteroid would pass through the inner solar system numerous times before striking Earth. We would have decades if not centuries to advance our technology and nudge said asteroid out of its intercept path. In short, there remains no undiscovered near Earth asteroid large enough to cause human extinction. Although such concerns make for great movies, we can lay that specific concern aside.

MEDIUM-SIZED ASTEROIDS
When one gets down to about 700 meter diameter asteroids, only about 50% or so have been detected. An asteroid of that size hitting Earth would certainly make for a very bad day. Fortunately the numbers of such large asteroids are low so that the odds of our being hit by such an asteroid are very small. But the other good news is that objects that large should be able to be detected days to weeks in advance and so give us plenty of time to casually evacuate the impact region. There would be no need for the loss of human life although some infrastructure might be lost. We would be able to recover from such an event.

THE SMALLEST ASTEROIDS
Asteroids below about 20 meters in diameter will break up and burn up upon entry into the Earth's atmosphere. If anything makes it to the ground it would be smaller rocks and a blast wave breaking glass -- a real fright but not particularly devastating.

SMALL TO MEDIUM-SIZED ASTEROIDS
However, it is the 20 meter - 150 meter or so asteroids that should really concern us. We know of only a small percentage of these asteroids and they are small enough such that we may not have much warning before they come. They are large enough to get through the atmosphere can cause significant devastation. The famous Tunguska impact is an example of this category of asteroid. What can be done?

What we really need is a good early warning system to detect them at least two to three days before they impact Earth so that we have enough time to evacuate. Rural areas can easily be evacuated of course but can a large (e.g. Miami-sized) city be successfully evacuated within that time frame? The answer is yes, city evacuations are frequently done when really bad hurricanes strike coasts. If needed, officials would convert both sides of the freeways to outgoing traffic and cities have numerous roads big and small to accommodate traffic. The further one gets out the more roads will be able to carry more vehicles. And people certainly would be willing to evacuate 24 hours a day. So an early detection system would be most helpful.

Fortunately there is work being done to set up a global early warning system. Specialized telescopes are strategically-placed around the globe will scan the sky each night and provide several days warning for these smaller impactors. We may get to the point where no one need die from an meteor impact.

DEDICATED SATELLITE
The B-12 Foundation is dedicated to setting up a sentinel satellite which would orbit between Venus and Earth. Looking outward from the sun, it would be able to more easily detect Earth-crossing asteroids that otherwise might go undetected. The Space Development Network believes that this would be a relatively low-cost solution to the small to medium-sized asteroid problem.