what is relevant is trying to estimate the total risk
Right, and I’m asserting that finding that risk from near-earth asteroids in the next 100 years or so is negligible should not affect the estimate of the total risk in any meaningful way (compared to the pre-NEO-survey estimate).
Now, for the actual estimates we’re interested in, that’s what is called the background frequency, aka unconditional expectations of impacts. The source for that goes to Chapman, C. R., and D. Morrison 1994. Impacts on the Earth by asteroids and comets: Assessing the hazard. Nature 367 ,33–40 which, unfortunately, is behind a paywall and I’m too lazy to scour the ’net for an open copy. The basic expectation of frequency of impacts, though, is visible through other sources (see e.g. http://neo.jpl.nasa.gov/risk/doc/palermo.pdf)
To re-express my point in these terms, the survey of near-earth asteroids does not change the background frequency.
(One of the nice things about my Xmonad setup is that I have a shortcut which yanks the current copy-paste buffer and searches Google Scholar for it; so the net effort looks like ‘highlight “Impacts on the Earth by asteroids and comets: Assessing the hazard”, hit mod-Y, right-click on PDF link, copy, paste’.)
Background frequency over a few hundred years or more, yes. Is anyone asserting that we should be planning out now exactly how much resources we put into this past anytime beyond the next fifty years or so? And if not, how is that relevant?
Are you saying that your current impact risk estimates for the next, say, 50 years are significantly lower than the background?
Yes. And we can conclude that because we have detailed understanding of the orbits of the big near earths and can predict their orbits out reliably for a few decades.
You need the assumption that (geologically) recent impacts that the background frequency reflects came from near-earth asteroids.
Yes, but we’re pretty confident about this also. It is very difficult for an asteroid out past 1.4 au to end up changing orbit enough to run into Earth. It requires a large force. It can happen if it gets just the right luck with collisions or with the right gravitational pull (such as if it happens to past just right near Mars at the right time in its orbit). But these events are rare, and moreover, we can model their likelyhood pretty well. Stochastic aspects of orbital dynamics are decently approximable by a variety of methods (such as Monte Carlo).
I don’t know about that. First, there are comets. Second, large forces are not uncommon with collisions in space. More to the point, any collision (or maybe even a close pass) could change the trajectory of an already-catalogued asteroid to something different and possibly dangerous.
The Chapman & Morrison paper points out that “Because of stochastic variability in the process of asteroid and comet break-up, there is a chance for significant temporal variation in the impact flux”.
I really don’t think we understand the movement of various objects in the Solar System well enough to declare “problem solved”.
Comets != asteroids. Comets have much harder to predict orbits (outgassing and change in mass both make them much trickier to predict). There’s some positive side here in that in order for them to be remotely close to us they generally need to be pretty visible (there’s some worry about comet remnants who are in weird orbits but are no longer highly visible when they are in the inner solar system area).
More to the point, any collision (or maybe even a close pass) could change the trajectory of an already-catalogued asteroid to something different and possibly dangerous.
Yes, and this is a problem, and I mentioned this explicitly in my last comment. The issue is how frequent such events are.
The Chapman & Morrison paper points out that “Because of stochastic variability in the process of asteroid and comet break-up, there is a chance for significant temporal variation in the impact flux”.
Yes. And what’s your point? No one is saying anything otherwise.
I really don’t think we understand the movement of various objects in the Solar System well enough to declare “problem solved”.
The argument isn’t that the problem is solved. The issue is that the chance of an issue in the short-term is much lower than we would have thought 10 or 20 years ago. That’s not the same as problem solved: the problem won’t be completely solved until we’ve got much better tracking (I’d prefer radio beacons on every object greater than 1 km) and have a system that can deal with sudden threats. But that’s not the issue at hand.
In the grand...grandparent I explicitly defined asteroids as anything large enough and fast enough to make a noticeable impact on Earth precisely to avoid terminology issues like this.
The argument isn’t that the problem is solved.
That’s how the whole thing started. If you go to the origin of this long sub-thread you’ll see CarlShulman saying “That’s mostly solved, all the dinosaur-killers have been tracked” and me replying “I don’t think so”.
The issue is that the chance of an issue in the short-term is much lower than we would have thought 10 or 20 years ago.
Yep—that’s what I mean by having an wrong estimate and then correcting it.
In the grand...grandparent I explicitly defined asteroids as anything large enough and fast enough to make a noticeable impact on Earth precisely to avoid terminology issues like this.
Ah, I see. Yes, in that case, using that broad class of objects, we have a much poorer understanding of comets then. The same basic argument goes through (because comets are not nearly as common an object as what is normally called asteroids), but not as by much.
. If you go to the origin of this long sub-thread you’ll see CarlShulman saying “That’s mostly solved, all the dinosaur-killers have been tracked” and me replying “I don’t think so”.
Yeah. I think Carl’s wording here is important. “Mostly solved” is different from “solved”. In this sort of context problems are very rarely solved completely, but more solved in the sense of “we’ve put a lot of effort into this, the most efficient thing to do is to put our next bit of resources into many other existential risks”.
The issue is that the chance of an issue in the short-term is much lower than we would have thought 10 or 20 years ago.
Yep—that’s what I mean by having an wrong estimate and then correcting it.
With respect to the wrong estimate—there is the “background frequency”, right? Tracking a bunch of near-earth asteroids does not lower it significantly (I am not sure, we may disagree on that). So if 10-20 years ago we thought that the threat of an asteroid impact was much higher, I think I’d call it a wrong estimate.
Right, and I’m asserting that finding that risk from near-earth asteroids in the next 100 years or so is negligible should not affect the estimate of the total risk in any meaningful way (compared to the pre-NEO-survey estimate).
Now, for the actual estimates we’re interested in, that’s what is called the background frequency, aka unconditional expectations of impacts. The source for that goes to Chapman, C. R., and D. Morrison 1994. Impacts on the Earth by asteroids and comets: Assessing the hazard. Nature 367 ,33–40 which, unfortunately, is behind a paywall and I’m too lazy to scour the ’net for an open copy. The basic expectation of frequency of impacts, though, is visible through other sources (see e.g. http://neo.jpl.nasa.gov/risk/doc/palermo.pdf)
To re-express my point in these terms, the survey of near-earth asteroids does not change the background frequency.
http://schillerlab.bio-toolkit.com/media/pdfs/2010/03/16/367033a0.pdf
(One of the nice things about my Xmonad setup is that I have a shortcut which yanks the current copy-paste buffer and searches Google Scholar for it; so the net effort looks like ‘highlight “Impacts on the Earth by asteroids and comets: Assessing the hazard”, hit mod-Y, right-click on PDF link, copy, paste’.)
Thanks.
Interesting shortcuts you have :-)
Background frequency over a few hundred years or more, yes. Is anyone asserting that we should be planning out now exactly how much resources we put into this past anytime beyond the next fifty years or so? And if not, how is that relevant?
Huh? Are you saying that your current impact risk estimates for the next, say, 50 years are significantly lower than the background?
Yes. And we can conclude that because we have detailed understanding of the orbits of the big near earths and can predict their orbits out reliably for a few decades.
That’s not enough to conclude that.
You need the assumption that (geologically) recent impacts that the background frequency reflects came from near-earth asteroids.
Yes, but we’re pretty confident about this also. It is very difficult for an asteroid out past 1.4 au to end up changing orbit enough to run into Earth. It requires a large force. It can happen if it gets just the right luck with collisions or with the right gravitational pull (such as if it happens to past just right near Mars at the right time in its orbit). But these events are rare, and moreover, we can model their likelyhood pretty well. Stochastic aspects of orbital dynamics are decently approximable by a variety of methods (such as Monte Carlo).
I don’t know about that. First, there are comets. Second, large forces are not uncommon with collisions in space. More to the point, any collision (or maybe even a close pass) could change the trajectory of an already-catalogued asteroid to something different and possibly dangerous.
The Chapman & Morrison paper points out that “Because of stochastic variability in the process of asteroid and comet break-up, there is a chance for significant temporal variation in the impact flux”.
I really don’t think we understand the movement of various objects in the Solar System well enough to declare “problem solved”.
Comets != asteroids. Comets have much harder to predict orbits (outgassing and change in mass both make them much trickier to predict). There’s some positive side here in that in order for them to be remotely close to us they generally need to be pretty visible (there’s some worry about comet remnants who are in weird orbits but are no longer highly visible when they are in the inner solar system area).
Yes, and this is a problem, and I mentioned this explicitly in my last comment. The issue is how frequent such events are.
Yes. And what’s your point? No one is saying anything otherwise.
The argument isn’t that the problem is solved. The issue is that the chance of an issue in the short-term is much lower than we would have thought 10 or 20 years ago. That’s not the same as problem solved: the problem won’t be completely solved until we’ve got much better tracking (I’d prefer radio beacons on every object greater than 1 km) and have a system that can deal with sudden threats. But that’s not the issue at hand.
In the grand...grandparent I explicitly defined asteroids as anything large enough and fast enough to make a noticeable impact on Earth precisely to avoid terminology issues like this.
That’s how the whole thing started. If you go to the origin of this long sub-thread you’ll see CarlShulman saying “That’s mostly solved, all the dinosaur-killers have been tracked” and me replying “I don’t think so”.
Yep—that’s what I mean by having an wrong estimate and then correcting it.
Ah, I see. Yes, in that case, using that broad class of objects, we have a much poorer understanding of comets then. The same basic argument goes through (because comets are not nearly as common an object as what is normally called asteroids), but not as by much.
Yeah. I think Carl’s wording here is important. “Mostly solved” is different from “solved”. In this sort of context problems are very rarely solved completely, but more solved in the sense of “we’ve put a lot of effort into this, the most efficient thing to do is to put our next bit of resources into many other existential risks”.
I’m confused here. What exactly are you saying?
With respect to the wrong estimate—there is the “background frequency”, right? Tracking a bunch of near-earth asteroids does not lower it significantly (I am not sure, we may disagree on that). So if 10-20 years ago we thought that the threat of an asteroid impact was much higher, I think I’d call it a wrong estimate.