I'm having a weirdly difficult time finding some basic ELI5 answers.
- What is the probability that this asteroid will hit us?
- What is the time interval where that probability applies?
- Do we have a probability distribution for where it might hit? I don't know anything about anything, but I assume we know what *general direction* it's coming from?
- Do we have a probability distribution for the potential blast radius?
In general, I am very confused by this news because "400m diameter asteroid 3% chance of impact" is something I would expect literally everybody to be talking about all the time. It's also something where if I learned that everything north of Kansas has a 5% chance of getting hit but everything south of Houston has a 1% chance, I'd seriously consider taking an impromptu vacation.
When a new potentially-hazardous asteroid is discovered, it's normal for the probability of impact to go up a couple times before abruptly plummeting to zero, as the radius of uncertainty shrinks until it shrinks past the Earth. See https://en.wikipedia.org/wiki/Torino_scale#/media/File:Apoph....
A 3% chance of impact right after discovery with the initial error ellipse isn't all that unusual; it will almost certainly be revised to 0 with more observation (and if it's not, you'll hear about it).
This makes sense, thanks. However, it doesn't mean that the 3% estimate of the chance of impact was wrong at the time of initial observation given data available, and that still makes it a huge deal at that time. At minimum, it would seem to justify using the best available instruments to characterize the asteroid more precisely as soon as possible.
If these large numbers happen so often that asteroids with initial impact probabilities of 3% are known to actually impact much less frequently than that, then the model is poorly calibrated, no? In other words, the reported probabilities aren't really probabilities and that is what has caused the confusion and anxiety in these comments.
It's not a model that is poorly calibrated - you seem to be taking a software-centric concept far away from where it's useful. The uncertainty at initial observation is because when you first observe an object, you only have observations covering a tiny bit of the orbit, resulting in very wide error bars. The "model" (Newtonian orbital dynamics) is one of the most precise models we have. Doesn't help when the observations are noisy.
Unless one in every 33 asteroids that have 3% impact probability at some point in time actually impacts earth, there is clearly some unwarranted assumption in the error bar/distribution calculation.
"The measurement data has noise" does not explain why the noise has a bias towards "the asteroid will hit earth" whereas reality so far has been biased towards "the asteroid will not hit earth".
(This assumes that significantly more than 33 asteroids have had >= 3% impact probability predicted at some point. The opposite would not be less concerning.)
To simplfy, let's assume you have perfect knowledge of everything else & that the only variable that matters is asteroids current position. By triangulating observations you have a point estimate. Due to calibrating your instruments in the past you know that they tend to have uniform additive noise that is the same in each dimension. Let's say it shifts measurements by up to 1km randomly.
So the best guess you have is that the true asteroid is 99% likely to be somewhere within a 2km box centered at the observation point.
For each possible location in this box you use it as a hypothetical starting point and run a simulation forward creating a trajectory. In 3% of these trajectories the asteroid hits the earth.
The 3% is only a probability over the measurement uncertainty. It represents our knowledge about the system in a bayesian sense. The true asteroid was always ever going to hit the earth or not. There is no uncertainty inherent in the system.
That many asteroids have non negligible probability only means the physics is sensitive to initial conditions or that the measurements are loose. (Both are true)
> Unless one in every 33 asteroids that have 3% impact probability at some point in time actually impacts earth
There would be a ~63.4% chance that at least one would hit us if there were 33 such asteroids. To compute this, take 1-(0.97^33). I agree with your broader point though.
That's because Earth has gravity, and an asteroid that comes close enough can get deflected onto the planet even if right now it seems to be on a trajectory to miss it entirely. The closer they get and the lower the relative speeds the larger the chance that they will collide and that's not a linear relationship. Beyond a certain boundary impact is certain, then the question is what the time of the impact is and how precise the observations up to that point are in order to figure out where and when exactly it will come down. That won't happen very long before the impact itself happens even if you could say some time in advance roughly in which hemisphere and roughly when. But not precise enough to be very useful.
Imagine you see a car 1 mile away as you're preparing to cross the street. 1 sec later, it's a bit closer. You wonder "will this car hit me?". It's hard to say since the car is so far away and your measurements of its speed are so poor.
You wait 5 sec and it's still only imperceptibly closer. You realize there is no way it could possibly hit you. You cross the street unconcerned.
In many situations, erring on one side results in worse outcomes than erring on the other side. In our case, a false positive has pretty much zero consequences, while a false negative could wipe out the dinosaurs.
If you have very wide error bars, shouldn't your estimate of impact probability be much lower than 3%? Most trajectories within your error bars will not intersect the Earth.
The 3% is likely the median of the probability range. You need more observations (and more accurate ones to narrow it further down, but for a first estimate it will do).
I don't know, but I suspect this is more about the limits of the observations (which I imagine are mostly from terrestrial observatories) needed to obtain much certainty about the object's size, course, speed, density, etc.
In hindsight this comment was too short. Clarifying some points:
By "This makes sense", I meant that this kind of thing can happen; as more data are gathered, the Bayesian probability of a candidate value can increase and then suddenly decrease. Here's a Colab notebook demonstrating the general phenomenon: https://colab.research.google.com/drive/1Eb1_humiGPdKb0c3qr_...
"Calibration" in this context means "statistical consistency between distributional forecasts and observations" in the words of https://sites.stat.washington.edu/raftery/Research/PDF/Gneit... . If the model's early forecasts predict impact with probability >3% for a class of objects that end up impacting with frequency much less than 3%, then the model is not well calibrated with respect to its early forecasts for those objects.
Based on the GP, it sounds like these early impact "probabilities" are no one's subjective (Bayesian) probability of impact because people who are closely familiar with this model know it is not well calibrated. The reported probabilities may still be useful to them as indicators or flags. However, those of us who are _not_ closely familiar with the model have found it confusing to see things that are not really probabilities reported as probabilities.
> If this has happed ~33 times then one will hit us.
There would be a ~63.4% chance that at least one would hit us if this happened 33 times. To compute this, take 1-(0.97^33). But I agree with your broader intuition that these predictions must be getting inflated.
Fair enough, but those are all relatively small, and detected only hours before impact, their effect would not be such that anything major would happen on the surface of the planet beyond some broken windows and maybe a sunburn.
Anything that size aimed straight down would most likely not reach the ground but burn up in the atmosphere and any remaining bits would just fall at regular terminal velocity.
But from 10 meters and up things change and the Chelyabinsk meteor is remarkable in that it (1) was large enough to have been detected but wasn't and (2) struck while we were apparently focused on one that was more visible but that ultimately missed us. We were very lucky that it impacted where and at the angle that it did, otherwise the airburst might have happened far closer to the ground or to might have impacted directly over much more populated territory. That would have been very bad news.
It doesn't matter how many 1 through 5 meter objects we can track because we have the atmosphere to protected us from the worst of these if we miss the 20 meter ones (or apparently even much larger) that travel at speeds high enough to give their relatively modest mass tremendous energy and for which the atmosphere does not give sufficient (or even any) protection.
"If it is real this IS the worst asteroid threat ever discovered and the impact location and times are ugly (will post pics shortly). Note that the impact is in the next couple days!
However, an Italian colleague of one of our astronomers suspects there is an error in the reported observations and there has been no chatter about this object and no followup. This probably means that it is not real.
" - Joel C. Sercel, PhD
I'm guessing the impact death area will be around 3600 km2 (I have no idea, please correct), so ultimately the chance of it falling on me is 1 in 10,000 to 1 in 100,000 provided the asteroid hits. Which means 1 in 1,000,000 to 1 in 10,000,000 in total? (assuming 1% hit probability)
> I would like to make an apology to the small body community. Some information was shared with me on an internal company message board that I did not have full perspective on and I posted a tweet, which I now understand was not appropriate. It was preliminary data and I did not have full perspective on it.
There is a disclaimer from the data source: “Scout data are about unconfirmed objects and all information should therefore be treated as potentially unreliable”
If I'm looking at the time chart correctly, that basically corresponds to "daylight hours", when you're facing the sun, tomorrow within the northern hemisphere...
We should look for secondary evidence, did the gov start continuity of gov operations etc. If it is real and if nothing can be done about it, we cannot expect official confirmation.
Well, that map tweet has now been deleted, and the guy posted this:
>> I would like to make an apology to the small body community. Some information was shared with me on an internal company message board that I did not have full perspective on and I posted a tweet, which I now understand was not appropriate. It was preliminary data and I did not have full perspective on it.
- What is the probability that this asteroid will hit us?
It's listed in the article: Impact probability 0.034, meaning 3.4% chance of impact.
- What is the time interval where that probability applies?
It's also listed: impact was estimated to potentially occur between 2023/08/14 04:48 TDB and 2023/08/15 12:22 TDB. (TDB seems to be UTC time without leap seconds? not sure). In other words the asteroid already passed Earth, and is currently no longer a risk.
> [TDB] is a relativistic coordinate time scale, intended for astronomical use as a time standard to take account of time dilation when calculating orbits and astronomical ephemerides of planets, asteroids, comets and interplanetary spacecraft in the Solar System. TDB is now (since 2006) defined as a linear scaling of Barycentric Coordinate Time (TCB). A feature that distinguishes TDB from TCB is that TDB, when observed from the Earth's surface, has a difference from Terrestrial Time (TT) that is about as small as can be practically arranged with consistent definition: the differences are mainly periodic, and overall will remain at less than 2 milliseconds for several millennia.
> TT is distinct from the time scale often used as a basis for civil purposes, Coordinated Universal Time (UTC). TT is indirectly the basis of UTC, via International Atomic Time (TAI). Because of the historical difference between TAI and [Ephemeris Time] ET when TT was introduced, TT is approximately 32.184s ahead of TAI.
I found this breakdown of JPL's CNEOS data to be every helpful. The close approach time chart shows % chance of impact vs day. From this I take it that we just didn't have enough info at the time of publishing.
Uncertainty in measurements make it almost impossible to tell where an object like this is going to impact, until we are hours, if not minutes away from impact.
> Since 1988 over 1,200 asteroids bigger than a meter have collided with the Earth. And of those we detected only 5 before they hit, never with more than a day of warning.
Is the first entry, and asterisk-marked, on https://cneos.jpl.nasa.gov/scout/#/object/ZTm0038 at the bottom, in the Observations section.
Unusual (new to me) format. Appears to me, first guess to read:
At least in terms of a public service announcement; I understand it's interesting for science but not so much for linking "hey look there's an X% chance of impact....yesterday!" on news websites
When I was taking physics at the University 20 years ago, one of my professors said that the closest we have ever come to predicting an asteroid impact was "whoa that was close" as it zipped by.
I find it very interesting even if the approach was yesterday, as the chances were seemingly quite high and asteroid was quite big. Also, Hacker News isn't exactly only news, just any interesting things, current or past.
I'm aware that it already passed its closest approach, but what does >3% even mean? 100% is >3%, but 3.000001% is >3% too. Was an impact certain at some point and the probability degraded to a bit above 3% over the course of the asteroid's trajectory? If so, I think I'd like to have a heads up when the probability is still closer to 100%, before it drops?
I think the link works just fine and I can see it's at 3.4% right now, but was mostly wondering why it's written as >3% in the title. Most likely it's meant as ~3% like other people suggested and I shouldn't be reading to much in it :)
Thank you for taking the effort to write your comment.
Edit: Not familiar with the site, but I get the sense that this probability reflects the latest run. The probability hopefully gets more accurate as observations rise?
I couldn't readily figure out how to see the probability at each of the 8 observations for this one (perhaps this is the first run it's included in--all 8 observations predate this run?), but the page for actual impactors (https://newton.spacedys.com/neodys2/NEOScan/index_past_imp.h...) at least implies that accuracy may improves with each (and then maybe flip to 0/100?)
Is there an english / eli5 if you like, summary of what this means?
I gather that today or yesterday an asteroid ~400m along it's biggest dimension ultimately came within x km of earth, that was close enough there was a nontrivial chance it would hit us? And this is big enough to make a 30 mile crater? And we only found out it was coming a couple days ago? Sounds like a pretty big deal if that's accurate.
It's accurate and it could have been a pretty big deal but for now it isn't, unless there are very low magnitude companions to it that hit unexpectedly because they have not been observed at all. There is some precedent for that sort of thing.
That would be an interesting analysis to see, my guess is it wouldn't be that different than if it was a sphere of equivalent mass, and vs a 400m sphere would be 400/(4*pi*200^3/3) = .0012% the volume (and so kinetic energy), and it would not penetrate in a way that does specifically worse damage. Just guessing though.
Edit: I confused radius and diameter in my calculation and revised it. I may have made other mistakes
Without fins, it's unlikely to go straight in. It would start tumbling, and probably break up and burn up. A sphere would more likely get to the surface intact.
If it has the same density than earth, it wont pierce deeper than its length. If it is made of uranium a bit over twice that (assuming earth is made of iron).
I wonder what the distribution is like; the most extreme length to height ratios we've seen for example. Not sure I've ever heard of something weirder than on the order of 2:1
That's just measure of uncertainty in out measurements, unless we're saying there was a ~3% chance someone would do an emergency asteroid redirection to make it hit.
I'm not sure if I did it right (I used the 15.84 km/s as impact speed, picked 45 deg impact, and an iron asteroid). It's certainly serious - millions dead - especially if it hits Manhattan as neal.fun seems to invite you doing, but not world-ending.
I had to guess without albedo data, but an H of 19.2 puts it in the 0.4 to 0.5 km range, so 400m could be on the conservative side. If it randomly has an albedo of 0.05, it could be as large as 0.96km
Not my area of expertise, but it sounds like a deep ocean impact would not be completely catastrophic.
With only ∼1% of the asteroid kinetic energy being converted into tsunami waves and with the stronger decay with distance implies that moderate size asteroids (100–500 m in diameter) striking the deep ocean basins off the continental shelves are not a significant overall hazard...
So like a 50% chance it wouldn't be that bad. Larger asteroids would vaporize enough ocean water to cause long lasting atmospheric affects.
Otherwise, a land impact would be somewhere in the 1-100 Tsar Bomba range energy wise.
Even that could be pretty bad if it turns out the object has lower Albedo than estimated. The difference between 500 meters and 1000 meters isn't all that big in terms of astronomical observations of a fast moving object and the composition is also quite uncertain and could add another factor of three or so to the potential impact. It could be very bad everywhere.
If you're looking at the "closest approach" distribution, that's not just for impacts, and the numbers are probability masses for the closest approach occurring on that day as opposed to some other day (not the probability of impact on that day).
In particular the MOID (Minimum Orbit Intersection Distance, the minimum distance between the orbit of the object and the Earth, in AU) is 0.0199 AU which is still 3 million km
Is there any action that could have been taken? Genuinely curious, I read about a test of some technology for deflecting asteroids a few weeks ago on HN, but I don't think we really have those capabilities yet?
There is likely a capability in the classified world to launch a vehicle to hit this object, but it won't be used because disclosing this ability would spark an arms race.
“Hit” and “do something useful” would seem to be distinctly different questions. A rock that you discover just before it hits us can’t be easily deflected, and even if you destroy it all of the mass is still headed our way.
I don't know what action could be taken. The risk of mass anxiety and the behavior that comes with that is probably greater than any additional safety a vague 3 day warning would provide.
I would want to know, especially if it’s a large object and higher percentage probability, because then it’s a way to tell loved ones what we need to tell them and go forward together in love. We should always strive to do this, of course, but it would still be better to have the opportunity to do it.
Oddly, I cannot find where on this page it says anything about the size of the asteroid in question. It's probably there somewhere, but I'm not seeing it somehow.
The chart is H vs. Albedo, and is awkwardly formatted.
H is the brightness observed on earth. Albedo is the inherent reflectivity of the object. What the chart is saying is that if we observe an object that is 19.5 H bright, it could either be highly reflective (0.30 albedo) and 310m across, very dim (0.05 albedo) and 760m across, or somewhere in between.
As I understand it, we can only calculate the albedo if we know the size and apparent brightness.
I'll note that the linked NEOscan page has an H of 19.9, while JPL's CNEOS has an H of 19.2.
True. At least it gives us a range this way unless it's a block of ice or whatever else. I still remember some of this from rendering days.
H is basically the same as M, an absolute magnitude, but for solar system objects. Difference being that for solar system objects H, as you've noted, is an absolute magnitude for an object 1 AU from Earth and 1 AU from Sun in a triangle where phase angle is zero meaning it's a straight line instead of a triangle and M is an absolute magnitude for an object (usually self illuminating) outside of solar system set at 10 parsecs from Earth. A star with M = 1 and a solar system object with H = 1 would roughly be the same brightness. It's a log scale, lower the number the brighter it is, so if you put that star at the same spot as the object it'd be a difference of about 26 where each unit is roughly 2.5 times brighter. What's interesting is that at zero it used to (roughly) be Vega (star). Both M and H are band-dependent, I guess it's V-band (visual or green-ish) if it's not mentioned. If you have B (blue) and V band, the difference between the two tells you a (visual) color which can be also interpreted as temperature, the lower the number the bluer it is and higher means red.
I'm all out of trivia for the night. I'm sure there are (amateur and not) astronomers and astrophotographers here that know this stuff way more about. All I knew is that without albedo you couldn't get to the size with absolute magnitude alone, we could if we had both absolute and apparent. What I didn't know if that apparently there's a rough table of correlation between H and albedo values probably based on most rocks we've seen in space around us.
Fair enough, that would definitely be a possibility. The dashcam and other videos from Siberia are still very fresh in my mind. That was a very close call. Slightly different angle in a more populous part of the world...
Which following the contained link to Terrestrial Time (TT) states that TBD is relativity corrected TT, which itself is about 30 +/- seconds from UTC -- something much more familiar to we groundhogs...
Of course 500 Km is a big difference with 400 meters but to those near the point of impact it wouldn't matter and the global effects would still be beyond anything in our history.
This is one interpretation of what this could look like:
The difference between the 500km asteroid impact in the video, and a 400m asteroid impact is the difference between a man jumping, and a man jumping to the moon.
Yes, it is the difference between a sterilization level event and one that is probably survivable. But it would still be the most significant impact in all of recorded history and to get to a larger one you'd have to go back a long, long time.
Looks like it is about the same size as 25143 Itokawa that the Hayabusa probe visited. That has a mass of 35 billion kg. The Burj Khalifa is 0.45 billion kg so that is about 80 Burj Khalifa's.
This, as I understand it, being the closest approach to our orbit, not our atmosphere or so. To put this in perspective, the Earth is some 6.4 Mm in radius, so that's 40-6.4 = 33.6 Mm above the surface.
MOID being minimum orbit intersection distance, for anyone else wondering. Sounded like someID (identifier) to me, was wondering why that value was given in AU
That tweet which had an image showing bands of latitude that it may hit and times (london/newyork ish tomorrow and day after) has been deleted by the author and now says "I would like to make an apology to the small body community. Some information was shared with me on an internal company message board that I did not have full perspective on and I posted a tweet, which I now understand was not appropriate. It was preliminary data and I did not have full perspective on it."
Well, no, because some have impacted Earth before. But if we limit ourselves to large bodies, yes. The current record holder is 99942 Apophis, which briefly had an estimated probability of 2.7% of an impact in 2029 (which has since been eliminated as a possibility). Apophis and ZTm0038 are around the same size.
If ZTm0038 does indeed have a 3% chance of impact, it would, like Apophis, land as a 4 on the Torino scale, tying the record for the most threatening asteroid in history. Unlike Apophis, however, the impact has a lead time of hours, not decades. Efforts might have been made to deflect Apophis; no such effort could realistically be made for ZTm0038.
It's worth noting that NASA's Scout page (https://cneos.jpl.nasa.gov/scout/#/object/ZTm0038) for ZTm0038 has a much higher probability of impact: of their 1000 sampled orbital solutions, 160 of them impact Earth. A 16% chance of impact for a 400m asteroid would put ZTm0038 on the border of a Torino 5, and would make it by far the most threatening asteroid ever discovered.
That said, note that the prior here has to be that an impact of such a size is very unlikely. Such impacts are exceedingly rare. The Tunguska event, for example, was an asteroid 1/8 the diameter (so 1/8^3 = 512 times smaller in volume) as ZTm0038, and it was by far the largest impact in recorded history. Since impacts roughly follow a power law, the much larger putative impact of ZTm0038 would be proportionately rarer, the sort of thing you'd see every hundred thousand years or so.
According to a site [1] pointed to by another post in this page, the estimate for "Minimum Orbit Insertion Distance" was about 0.02 AU or about 3 million km (in round numbers).
Luna's distance is roughly 384,000 km -- so call it 8 lunar orbital distances...
At 400m diameter we should expect an impact energy of ~3Gt, which would be one of the most energetic events in human history, if not the most.
For a comparison, the Lake Toba eruption (which is suspected of causing homo sapiens to almost go extinct 76kya) is estimated to have been in the 1-2Gt range.
This would wipe out an area equivalent to a mid sized country and would possibly have global effects. The threshold for that is somewhere between 250 meters and a kilometer but we fortunately do not have any data to make that much more precise. You definitely wouldn't shrug your shoulders and get on with life, it would be the most important event in your life assuming it didn't end. Depending on where it happened the economic impact of such an incident would destabilize the world economy for decades.
The public is unanimously in favor of funding asteroid protection mechanisms and research. It's even higher support than the military.
Naturally what do we do with that money and goodwill instead? Yes! Let's build a massive space telescope which takes pictures that are only marginally better than the other multi-billion dollar space telescope!
Protect the Earth? Fuck that, don't ya know kid? She's toast anyway because the Sun will explode soon! Also get in loser, we're going to Mars!
It seems any serious asteroid prevention program is going to require the learnings of "pointless" (as you might put it) scientific expeditions like putting an object into L2.
There have been many studies about what could be done to deal with asteroids that are on track to impact earth and the simple answer is 'nothing'. Frustrating, but unless you can think of something that none of the very clever people on those committees could think of it's going to stay that way.
There have been many studies about what could be done to deal with asteroids that are on track to impact earth and the simple answer is 'nothing'.
The National Academies report that you link to down-thread did not state that nothing can be done. They discuss multiple options, and they discuss which options would be most effective given different amounts of warning lead time. Figure 5.5 (https://nap.nationalacademies.org/read/12842/chapter/7#85) is a great high-level view of the option space.
A real message to take away from the "Mitigation" section of that report is that it's important to identify dangerous objects as early as possible.
No, the lead author is on the record as saying exactly that. The report is a fantastic read and chapter 5 (the mitigation section) leaves little doubt about the futility of any attempts to mitigate such a threat. Your chances of making things worse are just as large as making things better and given the masses involved your 'window of opportunity' is very likely going to be preclude doing something about an impact that you are 100% sure is going to happen. Of course if you want to feel good about this that's fine with me but this is just blunt physics, an impactor that weighs 8.4 billion metric tons (500 meter asteroid) isn't going to respond to much of anything that we do to it in the time between detection and the time that it will intersect Earth's orbit. And smaller ones are likely to go undetected right up to the moment that they hit.
The Siberian one was a very nice illustration of how completely blindsided we were and now that Arecibo is gone we have lost one very powerful tool in our arsenal that could have helped with this.
But don't let it ruin your day, the chances of this happening are very low, one in a million or larger.
(Doesn't make a huge difference but gives experimental validation of their previous theories.)
Some choice quotes from the report:
" As addressed in
Chapter 5, the time required to mitigate optimally (other than only via civil defense) is in the range of
years to decades, but this long period may require acting before we know with certainty that an NEO will
impact"
"The amount of destruction from an event scales with the energy being brought by the impacting
object. Because the range of possible destruction is so huge, no single approach is adequate for dealing
with all events. For events of sufficiently low energy, the methods of civil defense in the broadest sense
are the most cost effective approach for saving human lives and minimizing property damage.[+] For larger
events, changing the path of the hazardous object is the appropriate solution, although the method for
changing the path varies depending on the amount of advance notice available and the mass of the
hazardous object. For the largest events, from beyond global catastrophe to events that cause mass
extinctions, there is no current technology capable of sufficiently changing the orbital path to avoid
disaster."
[+] So, in the case of say the Siberian meteor if we had seen it coming (which we did not) you could have called on all the people in a 100 km (1/20th of a second of travel!) radius or so to go to the nearest shelter. This likely would have caused more injuries and casualties than the event itself did, but if the impact had been a bit more steep and closer to a city (or even in a city) then it may well have saved (some) lives. Note that that was only 18m across, was going close to 70 K km/hour, weighed 9000 tons and that it exploded nearly 30 Km up in the air.
"Finding: No single approach to mitigation is appropriate and adequate to fully prevent the effects
of the full range of potential impactors, although civil defense is an appropriate component of
mitigation in all cases. With adequate warning, a suite of four types of mitigation is adequate to
mitigate the threat from nearly all NEOs except the most energetic ones."
Note the careful qualifications, 'adequate warning' does a lot of heavy lifting there.
Pages 70 and onwards are pretty realistic and I think that the table really tells it all, none of the methods outlined are going to be practical given realistic times of warning and the kind of effect that you would have to create to make a meaningful difference in the outcome. Unless you happened to be able to pinpoint the trajectory with extreme precision and you had plenty of time and the impactor would be small enough. But that's playing the lottery. 'Civil defense' is code for 'shelter and evacuation', but assuming we're talking about an impact the size of the one that we are talking about here (400 meters, a couple of hours notice) utterly futile, especially if you don't know exactly where it is going to come down, you might end up moving people in the wrong direction, besides the mass panic. I don't want to be overly pessimistic but I'm with Jewitt in the sense that I do not believe we are geared up to deal with a challenge at that level.
Here it is in his own words in case you don't believe me:
I don't buy that. It shouldn't be that hard to launch a cloud of space drones that produce a lot of dusty debris when they hit. Have them adjust their courses when the incoming asteroid gets close.
That way, we could paint a huge smiley face on the asteroid.
I would much rather be exterminated by an asteroid with a smiley face than a big dumb pile of rocks. (Even if the smiley face keeps spinning out of view while it's coming in.)
The masses you're talking about are such that you'd need to detect the asteroid well before impact (ideally: years) and that your efforts would not accidentally make matters worse rather than better. Even then it likely won't do anything at all. Calling Bruce Willis on line 3... But agreed on the smiley.
I'm not sure if we're talking about the same thing. The smiley drones would work fine hitting pretty close to Earth, even an hour or two out. And the mass shouldn't matter much, just the surface albedo.
Oh. You're probably talking about deflection. Yeah, deflection requires massive lead time, way more ballistic forecasting ability than I suspect we're capable of (isn't a clump of rocks going to heat up and throw things off as it comes in closer to the sun?), massively efficient engines to match velocity, and a whole lot of wishful thinking.
The smiley face might still be useful in that implausible scenario, I guess, if it changes the reflectivity enough to let the sun slowly nudge it out of the way? It at least avoids the velocity matching problem; you're intentionally crash "landing" anyway. And spinning is probably ok, as long as Galileo was right and the sun isn't orbiting around the asteroid. It's not likely to head straight at the sun.
But as you say, intervention seems just as likely to make things worse as better.
The obvious answer to that is being able to reliably detect asteroids on a collision course, and compute where is it gonna fall in order to proceed the emergency evacuation.
But first you have to be able to detect it, second you have to do it with reasonable time to save as many people as possible
Again, these people aren't stupid. You will have a very large amount of uncertainty based on a series of observations which essentially project a circle of probability on the planet that shrinks as more information from newer observations comes in and then just before impact that probability will either drop to zero because it is deemed to be a near miss (sorry, George) or it will then become a certainty. By that time it will be too late to evacuate. I can dig up the report from one of these committees if you want (I should be able to find it), they make for very interesting reading, it is a really nice example of science at work, even if the result is a negative. Anything more advanced makes for great special effects in movies and science fiction but isn't going to work. You'd have a very short time to move the entire population of a circle with a radius of a few hundred kilometers to outside of that circle starting from the center. The longer you waited the fewer people you'd have to move but the bigger the chance you'd be too late.
