Some of what is known about near-earth objects and the risks of collisions from small asteroids in particular

Actually, a tremendous amount of solid data exists about the relatively small asteroid, 99942 Apophis and all calculations to date (12/2008) indicate that there is only a 1/45,000 chance that it's trajectory in 2036 will result in a collision with the earth's surface (and the likelihood of anything in 2029 is practically zero, but 2029 is when a possibility exists for the asteroid to pass through a "keyhole" region that could (back to the 1 in 45,000 likelihood) result in a 2036 collision course).

Here is a different perspective, [from http://timworstall.typepad.com/timworstall/2005/12/asteroid_strike.html]

At the peak of concern, Apophis asteroid was placed at four out of 10 on the Torino scale - a measure of the threat posed by an NEO where 10 is a certain collision which could cause a global catastrophe. This was the highest of any asteroid in recorded history and it had a 1 in 37 chance of hitting the Earth. The threat of a collision in 2029 was eventually ruled out at the end of last year.

Why ruled out?

Alan Fitzsimmons, an astronomer from Queen's University Belfast, said: "When it does pass close to us on April 13 2029, the Earth will deflect it and change its orbit. There's a small possibility that if it passes through a particular point in space, the so-called keyhole, ... the Earth's gravity will change things so that when it comes back around again in 2036, it will collide with us." The chance of Apophis passing through the keyhole, a 600-metre patch of space, is 1 in 5,500 based on current information.

OK, so this particular one was thought to be a threat, is now a great deal less of one and so we can all relax? Well, no, not really. An 1 in 5,500 chance may be fairly small but the damage it would do if it did happen would be fairly large. Traditionally one is supposed to multiply the chance of an event occuring by the cost of it occuring in order to get the expected cost. If the cost were, just as an example, $10 trillion (not unreasonable BTW), then with a one in 5,500 chance that expected cost would be some $2 billion. We’d therefore be logical (ignoring things like discount rates) in spending up to $2 billion in trying to avoid such an occurence. The unfortunate part of this calculation is that that one in 5,500 is the chance of this specific asteroid hitting us in that specific year of 2036. When we look at the grander picture, the chance of an asteroid hitting us at some point approaches one. It’s virtually certain to happen (but we don’t know when which means that to be complete, we do have to use discounting but I’m not going to do the math).

[from http://timworstall.typepad.com/timworstall/2005/12/asteroid_strike.html]

There are two fundamental points, facts, irrefutables, that need to be considered:

1. 99942 Apophis is known, identified, studied, in great detail. So are many other asteroids. But there are a lot of others out there that we simply don't know about, period. We do not have a "God's Eye" radar system that works across a span of billions of miles of space, and while we are very well equipped to calculate what could be a threat years and decades out, for an identified object, that does not help us for those which may not be detected until, perhaps, five or ten years out, or perhaps even less. It's a reasonable claim that we will not be suddenly surprised with only weeks or months advance warning, true, but in our present zero-stage level of response readiness, even five years' or ten years' advance warning is not much. Look at us now. 99942 Apophis has been a known commodity for many years, and we are doing hardly nothing and we are fresh into 2009.

2. We have made and continue to make unrealistic assumptions that could come back to haunt us. The belief system that looks upon 99942 Apophis (for one clear example) as a zero threat on the Torino scale, just a 1 in 45,000 chance of a collision anywhere with the planet, does rest in part upon assumptions regarding the constituency and distribution of mass within the asteroid as well as regarding the interactions of the asteroid with any unknown objects throughout its projected orbital cycle between now and 2029 and also 2036, interactions that could modify its path in 2036 slightly, for better or for worse, relative to the Earth.

These unknowns do not imply that there will be a change that brings 99942 Apophis into a collision course, and any such unexpected trajectory modification could result in an increased margin of safety. The point here is simply that we do not have sufficient information to just take a long rest, kick up our feet, and lay on the sofa like "couch potatoes."

There is another relevant fact.

Any and all serious and collaborative efforts on an program to have a space-based defensive response to asteroid collisions will absolutely have benefits for all sorts of other industrial, scientific, economic purposes, such as are described about the ASTRIC program and projects - energy sources, power generation, mining, manufacturing, colonization, medicine, agriculture, social networking and reduction of global conflict (to name a few!).

Thus, we have a Win-Win situation here. Every dollar, every euro, spent today and tomorrow on something like ASTRIC, focused on this asteroid collision avoidance problem, is an investment into our collective short-term and long-term benefit and gain, for Everyone. Even if there is not any asteroid that needs to be lasso'd, corraled, and redirected away from your home and your head.