My, it’s a red-letter day. I’m compelled to disagree with Iain Murray twice in a single day, on two different subjects.

The Professor is worried about asteroids on InstaPundit.Com. I take his point that he’s not worried about this particular rock, but Steve Milloy’s point on JunkScience.com is important here:

Gasp! Shock, horror! Er… hang on. Doesn’t this particular rock cross the orbits of Mars, Earth, Venus and Mercury (twice) every 1,321 days (3.6 Earth years)? And hasn’t it been doing so for millions of years? Wow! That was a close call alright…

Mr. Milloy is indulging in a fallacy here, similar to the one of the man who jumps off the building, and calls out as he passes every floor, “Doing fine so far!”

It was a very close call in astronomical terms. And in fact it doesn’t “cross the orbits” of those planets with any regularity–space is three dimensional. There is no way to know for how many millions of years that particular object has been avoiding hitting planets (it may be a chunk broken off from a larger one that did, in fact, collide with some planet, such as our own Moon).

Of course we shouldn’t lie awake now sweating over the fear that this particular object will hit us the next time around the carousel. The point is that it’s a reminder that many such objects are out there, some of them have our number on them eventually (as evidenced by past extinctions, and the cratered surface of the Moon, which didn’t get that way from too many sweets during adolescence), and that now that we have a civilization worth saving, and the technical means to save it, we should be thinking about it and devoting appropriate resources toward that end.

Of course we must colonize whatever worlds we can, but at the moment that’s beyond us. So let’s just keep on with our lives until we have the technology. Until then it’s best for us to treat this as the interplanetary equivalent of crossing the road. Look both ways, don’t build a bridge.

I’m not sure what Iain’s point is here. It is not, in fact, beyond us to colonize other worlds now–we simply choose not to. Will it be more affordable in the future? Of course. But that rationale can also be used to put off forever the decision to buy a new computer.

When he says, “just keep on with our lives until we have the technology,” one might infer from that that acquiring this magical “technology” is a passive act, like receiving manna from heaven, or cargo from the airplanes and control towers built from palm fronds. Technology is something that we develop (active voice), in response to some perceived need. Glenn and I point this little event out as a reminder that there might be reasons to develop space technology sooner rather than later.

How much we should devote to such an endeavor depends on the expected value of it (i.e., the probability of a catastrophic extraterrestrial event times the cost of it should it occur). I haven’t done that computation, partly because I don’t know the probabilities (because we aren’t even spending the trivial amounts necessary to adequately fund the sky surveys to gather the data with which to do so). But it’s certainly not zero, which is approximately how much we’re currently spending on it.

And as for “…Look both ways, don’t build a bridge,” I have no idea what this means in the context of the discussion. The point of the article was that even if we “look both ways” (right now, as I said, we are barely looking at all) we currently have no policy options if we see the car is bearing down on us–bridges are entirely beside the point.

[Update at 10 PM PST]

A reader who calls him/herself “skeptic” asks:

What is the probability and how was it calculated? If it is based on known events and conditions, that is fine. But what is it?

As I pointed out, we don’t know, because we haven’t even spent the money needed to gather the data necessary to do the calculation. The known events are many (e.g., in 1910 a meteor or comet known as the “Tonguska Event” hit a remote region of Siberia. Had it occurred in a populated area today, it would have caused billions of dollars in damage, and thousands, perhaps millions, of lives).

If it is based on what we don’t know, that is *not* fine. I don?t care what it is; it is speculation.

So we should ignore it if it’s based on willful ignorance?

What can we do about it? It would take a massive, massive amount of energy to alter the orbit of anything substantial.

Do you have some calculations to back up this claim? In fact, the amount of energy required to divert an object from its path sufficiently to prevent a collision with earth is quite small.

Hydrogen Bombs would be insignificant.

Ummm… no. Do you have any idea whatsoever what you’re talking about?

Even if we could amass the required energy, how would it be delivered?

By landing a small probe on the body, setting up a solar-powered or nuclear de-vice that could utilize its own mass as a rocket to divert it the few meters per second that would be required to prevent the catastrophe.

I am all in favor of space exploration. But I am not big on tax-funded research: who gets to set priorities? Politicians ? I hope not. Speculators ? I hope not. Scientists – How do we choose?

I said nothing about tax-funded research. Presumably we would choose based on who would do the best job of providing results.