16 February 2013, 17:32

Russia's meteor too small to track; no relation to asteroid, experts say

Russia's meteor too small to track; no relation to asteroid, experts say
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Experts everywhere are continuing to analyze the shocking meteor that crashed over the Urals in Russia on Friday morning, injuring close to 1,000 residents and causing structural damage to hundreds of buildings.

Jim Zimbelman, a geologist at the Center for Earth and Planetary Studies at the National Air and Space Museum, about the strike and what we can do to spot, predict and protect ourselves:

We continue our coverage today looking at a meteor strike which hit five cities in the Urals in Russia, leading to what some are estimating 1,000 injuries. Here to talk about the meteorite strike and our ability to predict and understand them is Dr. Jim Zimbelman, he is a geologist at the Center for Earth and Planetary Studies at the National Air and Space Museum. Everyone was looking at the skies today but for a very different reason. This is quite a coincidence that DA-14 happened at the same day, right?

It is and I was interested to hear NASA spokesman this morning, making it very clear that the two were completely unrelated in their orbits.

And in terms of this meteorite, was there any warning, is there any ability to have a warning for an event like this?

Yes there is. The question is at what size limit do we no longer detect things and that has been a point of discussion for quite some time. Starting many years ago but really getting in earnest about ten or fifteen years ago, NASA has been supporting sort of grassroots efforts by some amateur and professional astronomers to look for asteroids that could be civilization-threatening, the ones that would really be an enormous problem for the whole Earth. And NASA has enabled that kind of search to be quite thorough for these catastrophic ones. I think, the last estimate I’ve heard that there were over 95% of the ones that we think should be out there, that would be a size that would be, you know, end-of-civilization kind of event. We know where just about all of those are. The problem is the smaller they are the harder they are to detect and where exactly is that cut-off. It’s probably slightly larger than today’s meteor strike. That is even with this wonderful program that is ongoing now between NASA and several other countries I seriously doubt that we would have easily detected the object that hit this morning.

But even with those colossal, those 1,300 multi-km large asteroids, half their orbit isn’t completely easy to predict because of the way it’s impacted by gravity, it’s impacted by the Krasowski effect and other factors. So, how might we be able to impact something that might even be more manipulatable?

That’s a very good question and today’s close fly-by is a good illustration of how NASA deals with that. When an asteroid is detected that could be coming somewhere near the Earth, what really refines the orbits precisely, that gives us much more confidence, is when we can bounce radio or radar signals off of the asteroid and, actually, track it for a while. And that is what gives us very very precise orbital information. Today’s close fly-by was a situation when this asteroid was only discovered last year but that gave radio astronomers enough time to detect it to the point that JPL and the people who do these orbital calculations had a very high degree of confidence that it would not hit us and knew that it was going to be close but it was going to miss. My understanding is that it was a direct result of being able to get some of these much more precise radio-based observations to back up what we might get from a telescope. A simple telescope discovery may not give us an orbit determination good enough to allow us to be very confident that we knew where the thing was going.

Now one of the things that some might wonder is when we launch a rocket up and the capsule begins coming down we’re able to estimate probably within half a mile, certainly a couple of hundred meters, where it’s going to land – somewhere on the ocean or wherever. Now part of that we know is the launching point but why is it so much harder with the meteor or meteorite?

It, actually, relates to what we’ve just talked about that with our own spacecraft we’re tracking their radio signals and doing the same kinds of orbit calculations real-time while the thing is going up. So that we have this much more precise electro-magnetic radiation-based determination of its orbital properties than we do of a natural object. If one is discovered and we don’t know anything about it before some telescopic discovery, we have to be really fortunate to be able to make the kind of radio astronomy measurements that would allow us to get a really precise and accurate orbit.

Now my understanding is that the object which struck today originally was about 10 meters across and when it hit the surface it broke up into many-many pieces of much smaller size. Why does something that size cause such considerable damage?

Good question and the best analogy is to an event that happened in 1908 in Russia as well. Doesn’t mean Russia preferentially gets hit but it is a very large nation so it’s got a lot of area where things like this can happen. In 1908, a very similar sized object to what you’ve just described blew up in the atmosphere above the Russian forest and it flattened a whole bunch of trees. Why did it do that? Well, we think that’s very similar to what happened today that as these objects are coming towards the Earth they’re going through Earth atmosphere and its atmospheric density is getting thicker and thicker as we get closer to the surface and at some point the pressure of the atmosphere that it’s running into gets so great that it causes the thing to fragment. We use the word explode but it literally just completely disaggregates itself at some elevation. The Tunguska event was estimated to be 5 to 10 km up. I would bet today’s event will be a very similar kind of distance. I have heard some reports of small pieces reaching the ground, and that’s the result of once the larger, 10m or so object, broke up and then the little guys not only going slower but they will have a better chance of surviving and reach the surface of the Earth.

Now in terms of damage to people, to animals, to living things. Is most of the damage happening through shrapnel and through secondary collisions with objects or is it also risk of radiation or other kind of damage happening?

Again, going back to the Tunguska analogy, to what we think was similar to today. It was less the fragments themselves that caused damage to the forests or to the animals than it was this catastrophic disruption at an altitude in the atmosphere and it was the pressure wave caused by that enormous disruption, that’s what caused damage and in fact I think that this is consistent with what I’ve been hearing today. Most of the injuries to people have been glass windows that were shattered by the pressure wave generated by this object’s passage through the atmosphere and its disruption caused the sonic boom, a very strong one, one that was strong enough to break glass. At least the few reports I’ve been able to read from Russia itself, implied that virtually all of the injuries were from the glass. It’s sort of like the shrapnel you were talking about but it doesn’t come from the object itself, it’s result of the pressure of the disruption when it hits man-made objects that generated the fragments that caused the injury.

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Dr. Ed Beshore, a deputy principal investigator for NASA's OSIRIS-REx asteroid sample return mission, about the meteorite strike:

Today, over the Urals in Russia, meteorite crashed to Earth into five cities moving at supersonic speeds has led to hundreds of injuries and considerable damage. With some reports indicating that the number may be nearing one thousand. To take a look into the strike and what we can do to spot, predict and protect ourselves, we are joined by Dr. Ed Beshore, a senior staff scientist at the University of Arizona, a deputy principal investigator for NASA's OSIRIS-REx asteroid sample return mission.

The tragedy of this meteor strike is still unfolding and so far we are hearing reports as many as 900 have been injured but let’s take it a step backwards. How good are we at understanding where and how meteors or meteorites rather can strike?

Well, we’ve actually been looking for these kinds of objects for over ten years. Of course, the real risk that we’ve been trying to address with the recent surveys over the last decade has been to find objects that are much much larger than the object that entered the Earth atmosphere this morning over Russia. We are still getting information about the proposed size of this but I’ve seen numbers based on measurements suggesting it was about ten meters across which is not very large as these things go. Something like this happens about every century. And small objects - ten meters across - are right now well beyond our ability to track over a period of time and predict their orbits. In 2008, we were able to discover an object of about of this size but only about twenty four hours before it actually struck the Earth and it entered the atmosphere over North Africa. So, right now, if we find something like this, it’s generally a lucky occurrence, what our effort is to find these objects that are much much larger, over 1 km in size.

So there really isn’t any way at this point where we can get people forewarning and when basically not until the meteor hits the atmosphere?

Right now, I would say, it’s probably correct that it’s pretty difficult for us to find objects of this size. We do find them, but we only find a small fraction of them because the ground-based telescopes that are used for this purpose simply don’t have the requisite light-gathering power to see these small objects far enough in the distance so we can accurately predict their orbits and then determine what their impact is.

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