The main reason that these small asteroids are noticed only days before they come to closest approach is because they are small. They are not large enough for us to notice while they are still farther away.

The article notes that the scientists needed three observations to calculate the meteor’s orbit. Interestingly, if you have distance information, it only takes two observations. In the movie “Roxanne,” the title character says that she thinks she discovered a comet but wouldn’t know for a few days. This is because comet hunters need three observations to calculate the object’s orbit to verify that it is in a cometary orbit; they have no distance information.

Robert wrote “The article spends most of its time selling a computer model the scientists have developed that they claim can predict the approach trajectory of meteorites, something I find quite unconvincing.”

I think I understand the reasoning that they apply. They associate their “Monte Carlo” type of model with orbits that resemble already known asteroid orbits. Where there are a number of similar asteroid orbits, then the conclusion seems to be that there are even more, so we might expect asteroids that land in various locations on Earth to come from directions that match their “predictions” for the various locations.

If future sightings match their predictions, then the value may be in concentrating our meteor-searches in the directions that are likely to fall in areas that would be most adversely affected. Fortunately, we now have lots of cameras around the planet, so sightings may become common enough for the model to be well tested in the next few decades.

Although, with luck, we will have already found all the dangerous asteroids by then.

Andrew_W: You make a very good point that I should have considered. The question remains: Would a nickel-iron asteroid of this size (several meters) and weight (about 350 tons) produce any significant damage?

I suspect not, in most cases. Only if the asteroid is coming in from a high angle orbit at great speed would it pose a greater threat.

It seems likely to me that this was a C-type meteorite, if it had been a several hundred ton S or M-type it may have hit Earths surface mostly intact.