This is a profoundly dumb summary of the referenced research article - rather astonishing for UCLA.
Studying the boulder swarm - amazing! Saying the boulders that came off are like shrapnel from a hand grenade - sure. Observing that the boulders keep the relative velocity of the original body and that they could cause damage if they hit something... ok yeah? Interplanetary velocities are energetic - true - and that this is similar to the energy of the Hiroshima atomic bomb - technically true also, but this is where it veers into sensationalism.
It's rather telling that this part is put as "Jewitt said" but not quoted. This could very mean that Jewitt said it would have X amount of energy, and the author decided to put in the nuclear bomb angle because it was a similar energy.
Asteroids this size just burn up. "In theory" they could hit something in orbit but space is mind-bogglingly huge and this is exceedingly unlikely. And weighed against surface impact of something judged worthy of a planetary defense scenario?
Wouldn't breaking up a planetary defense worthy asteroid into medium to even large boulder size asteroids be considered a win? Whats the limit on asteroid size that can make it through the atmosphere? And even then, intuitively, it would seem like the destructiveness is going to scale with the size of the individual asteroid, so a rain of many smaller asteroids making it to ground would be far lower than one large asteroid..
It depends on what the threshold for 'planetary defense worthy' is I guess. If you shattered an asteroid, but all of the asteriod pieces still entered the earth's atmosphere, then you're going to end up releasing pretty much an identical amount of energy.
At "city buster" size of impact, this would probably be beneficial. But beyond that? Probably not hugely beneficial. Probably effectively the difference between a ground detonation and a partial airburst.. so maybe less ejecta (reduced global dimming after). But... probably not a meaningful change.
Yes the energy is identical, but the volume across with the energy is dispersed is the benefit. Even if you "only" break up an asteroid so that the rubble falls all over the world across a few days or weeks, that's nothing compared to the asteroid in one piece hitting.
It's not the fall, it's the sudden stop at the end. Make that fall over days/weeks and a million times the area, you're fine.
It's all going to fall at basically the same instant.
At small rocks destroying them is a good thing. At big rocks destroying them is worse than not shooting: Blast radius goes at the cube root of energy, blast area goes at the square of blast radius. Thus if you were to break an incoming rock into 8 equal parts the blast radius of each impact would be halved, the blast area quartered--but there would be 8 hits, for a final result of doubling the blast area. The smaller the pieces the worse the effect until you get down to the point where they burn rather than hit. (And that brings it's own problems with flash heating.)
Thus big rocks must only be deflected, not destroyed.
> It's all going to fall at basically the same instant.
No, not for any sane definition of "at the same instant". See Shoemaker-Levy 9 as a great analog. Completely natural forces broke it up and it fell across a huge swath of Jupiter. An engineered breakup would of course be much more fine tuned to create both chunks and vectors of our choosing.
If something were to head at us, and we took it from one big chunk to multiple smaller chunks but with such a terribly small explosion that we turn it into a closely-spaced fleet of rocks, then yes, but hopefully if we go through the effort of trying to destroy/deflect, we'd use a reasonable amount of explosive.
While your energy dispersal functions in a vacuum are correct, you're completely neglecting everything else about the situation. All the energy we're putting into the system to change the vectors to start with, you're acting like we barely tap it. Look at what happened with DART and that had zero explosive, that was _purely_ ballistic. You hit a rock several months out and send pieces flying in 18,000 directions, some hit us, some don't, they hit across weeks, they hit across the world, and you get the benefit of our atmosphere. Presuming optimal angle of attack for the interloper, everything under 100 meters in diameter is vapor. More acute angles take that number up, and at really steep angles the objects skip off the atmo. Larger rocks will airburst from the entry into atmo, and lots of stuff will make landfall, but again, ALL THAT ENERGY IS DISPERSED ACROSS SPACE AND TIME. I know you said it won't, but the math, and real-world examples, say it will.
> Thus big rocks must only be deflected, not destroyed.
The problem is most things aren't just big rocks, the things that endanger us also consist of rock piles and slush balls, which you cannot deflect. So we MUST engineer for destruction as well.
And this discussion itself also ignores a hundred other variables such as orbital mechanics, how much time we get, composition, etc. To just say "It'll all hit at the same time and we can only deflect" is only correct, pardon the pun, in a vacuum. There's more to consider.
All of this depends on the actual parameters we are talking about
> last radius goes at the cube root of energy, blast area goes at the square of blast radius.
Only up to the point at which the blast wave touches atmosphere then strange things happen because the blast is now being tunneled into a vacuum. This likely reduces the blast of very big asteroids by channeling most of the energy back into space. However blast area isn't the only concern. An ice age can be triggered if enough matter is blasted into the upper atmosphere. You might increase the blast area by breaking the asteroid into smaller pieces but completely eliminate the risk of depositing light blocking particles in the upper atmosphere.
It is by no means guaranteed that if you break a big asteroid into eight pieces, they will all hit. The energy to split an asteroid may confer sufficient momentum that small if not all the pieces miss the Earth.
Still depends on the amount of energy being released. Burning up a large enough asteroid would cook the planet, even at days/weeks/months. I guess it really depends on the rate at which heat is lost to space.
But won't they burn earlier in the atmosphere due to exposing bigger surface to it? AFAIU small asteroids burn in the atmosphere and thus don't reach the surface or reach it in very small pieces (and presumably more distributed if a bunch of them at once), vs. big ones burning less in total and hitting more concentrated; do I have it wrong?
Yes, but planet killers can be mind boggling large. The 'dinosaur killer' was estimated to be 72 teratonnes of TNT equivalent. Even if you spread that perfectly evenly over 10 days, that's a 83 MT nuke going off every second.
Or taken another way, the dinosaur killer had an total estimated energy of 300ZJ - 3x10^24J. Total solar energy is 44 quadrillion W (4.4x10^16 J/s). Even spread over 10 days (864000 seconds), that results in an excess 3.5x10^18 J/s.
Which is why I said it depends on what your threshold is. Certainly somewhere between city buster and dinosaur killer lies the tipping point.
But you're not going to meaningfully spread the energy over time. If the bits are going to hit that means they didn't move more than 4000km after the strike. Assuming they're distributed in a sphere that means none hits more than 4000km early, either (and likewise 4000km late)--and since we are talking about objects with a relative velocity of a few km/sec that means it's dispersed over at most a couple of hours.
By the back of the envelope you're looking at about a megasun.
Once again, a scenario where letting the rock just hit is not as bad--energy spent gouging a huge crater is energy not spend blasting civilization.
Since you're discussing Teratonnes, I'll link a discussion from X which is about what a 10GT nuclear warhead ignited at 80km altitude would do just thermally. Crossed my timeline just recently and has a link to https:// apps.dtic.mil/sti/tr/pdf/ADA 383988.pdf if you don't like https://twitter.com/ToughSf/status/1689305541422575623
Dangerous asteroid sizes span many orders of magnitude from the smallest real global danger to the largest. Breaking one up would work for asteroids over maybe tgevlowest order of magnitude size range, but that still leaves many more orders of magnitude in larger sizes for which it wouldn’t help you much.
As important as the DART mission was, we are still quite far from actually defending against a mass extinction sized asteroid or even comet. The Dimorphos asteroid, which was hit by the DART craft, has a mass of only about 5 * 10^9 kg, while the Chicxulub asteroid (which caused the Dinosaur mass extinction) had a mass of 1 * 10^15 to 5 * 10^17 kg. That's six to eight orders of magnitude difference, or a factor of one million to 100 million.
Somebody has probably calculated the details, but I suspect if we have to hit such a large impactor, we have to launch as many hydrogen bomb equipped Starships at it as we can. And our time window might be quite short. The worst case is if it's actually a comet, as these are hard to detect in advance, since they aren't aligned with the plane of the solar system.
By the way, if you Google for "DART mission" or "Chicxulub impactor", be careful, something might hit your search results...
But if detected early enough it might not take much more than a DART sized nudge of even a Chicxulub sized asteroid to change it’s course enough to miss the Earth. The whole reason DART targeted a two asteroid system was so we could measure how much we changed Dimorphos orbit around Didymos. If we have to blow these things into rubble shortly before impact we might be in big trouble.
DART nudged it's target about 2.7mm/sec. To ensure a miss you need a sideways deflection of up to 4000 km (depends on the geometry.) To generate a miss by Dimorphos assuming the worst case you're looking at 1,481,481,481 seconds of lead time. That's about 47 years. Against the dinosaur killer you're looking at a lead time far beyond our ability to predict orbits.
Note, also, that if you're throwing kinetic stuff at your target you get little choice in how it hits, you very well might not be able to shove it to the side.
Despite the refusal to consider the option there really is only one choice against a major threat: Orion. We know it works (it has been flight tested with conventional charges, it has been tested with single impulses with nuclear charges), while there are some serious question marks about whether you could actually build an Orion capable of launching form Earth (how do you keep the pusher plate from getting too hot??) that does not apply if you're using it against an asteroid. You don't care what shape the asteroid ends up in, just that it get out of the way. Your only limit is that you don't want to make any given shove big enough to risk breaking the asteroid.
By a crude approximation you can easily get 10% of the bomb energy to show up as impulse, this can be increased by putting the bomb closer (remember, you don't care about damage short of destruction) and some still-classified data says that it's possible to build a shaped charge that directs the majority of it's energy at the asteroid. Obviously, exact numbers are not known to us mere mortals.
With a ten kilometer Chicxulub class asteroid, blowing it into rubble is not on the table anyway, even with rather large hydrogen bombs. We can only hope to deflect them.
We're just living the untold years before futuristic space defense systems that exist in so many books, movies, and videogames. All that stuff must have passed through numerous iterations of failures and catastrophic mistakes, in their respective fictional worlds. So here we are, in the real one.
Consider me skeptical we’ll ever make it there. Not because it’s beyond technology, but because I don’t have a lot of faith that humanity will be surviving the next 200 years.
I see this kind of negativity all the time, usually over climate change and environmental destruction. Those things definitely can impact the human population. They can even end our current civilization as we know it, which is somewhat fragile. But humans will survive, we’re extremely adaptable and hard to exterminate. We live in every terrestrial biome.
There are two things that could actually end us. One is a celestial disaster powerful enough to sterilize the terrestrial part of the planet. That’s very unlikely, but not imposible. The other is we replace ourselves with a competing organism, either biological or mechanical that’s not human, doesn’t need us, but is so much better than us at life that we can’t compete. Like general AI with a physical presence, or a genetically or cyberneticly modified super-human that lacks humanity, that we wouldn’t consider human. Those are highly possible scenarios over the next 200 years.
Yes, the annihilation of humanity is basically impossible in the near-term without a celestial disaster, but the functionally-permanent end of modern civilization is not.
Like, reasonable scenario: Climate change causes mass starvation and environmental inhospitability. Mass-deaths and some very violent migration happens. The last few years have showed us how fragile our infrastructure is, right? Between covid-shutdown supply-chain problems and the Russian invasion of Ukraine, we're seeing how fragile civilization is.
It's not crazy to imagine privation leading to violence leading to destroyed infrastructure leading to more privation in a vicious cycle.
This ultimately could lead to a return to a comparatively primitive society where anything that relies on sophisticated supply-chains is out of reach. Like moving 100 years back in time. But the tech of the day depended on far easier mining, sources which are now mined out. So we've destroyed the bottom rungs of the ladder that we no longer need... until we do.
And also, industrial-age tech is carbon-intensive. Is it possible to build decent solar cells and wind power without a global supply chain? Or will we burn down the world for power, causing even more climate change, which will create another vicious cycle?
So we could be looking at a technological and civilization-level regression that wouldn't be remedied until another geological era.
This is quite possible. Not easy, but possible. What you say about us destroying the bottom rungs of the ladder behind us is very true. Civilization, as we know it, is much more fragile than humanity.
Disagree--a disaster doesn't need to kill all humans in order to take us out. All it needs to do is kill enough of the population that what's left can't survive.
We've already seen localized extirpation of humanity this way--many areas of the New World were depopulated by disease. It was probably not a 100% kill but if the survivors don't have the right skills (and note that most people do not have the right skills to survive in a collapse scenario) they'll die anyway.
Survivalists always are about maintaining existence at a lower tech level--but that's relying on things they can't replace. That's not going to be viable in the long term. Not to mention the problem that sufficiently hungry people will go after any stores of food they're aware of.
> All it needs to do is kill enough of the population that what's left can't survive.
Obviously. That’s very low though. From history we know we survived a near extinction event where the human population declined to the neighborhood of ten thousand.
A long time ago I dated someone whose Dad worked with nuclear weapons before the nuclear test ban was in place and at the height of the Cold War. At the time there was a saying that it would take less than a dozen nuclear weapons to destroy life on earth if detonated in the right location. Her Dad had told her that the number was more than a dozen but less than a hundred and was pleased to be one of the few that knew the exact number.
You're on a road, on foot or small vehicle, and you see a truck coming on collision course. What to do? You get out of the way.
Obviously we can't deflect Earth from its orbit. This project showed we're able to deflect 'small' asteroids. In time, we may be able to deflect bigger ones.
@ Some point, there will be an incoming asteroid that's too big to make it avoid collision. When (not if!) that happens, only option might be to escape into space, watch Earth being hit, and maybe return there some day.
Chances are this will happen so far in the future, that humans don't exist any more, or have moved to other planets or even star systems, with Earth being just one of many homes.
So... who cares. As long as we can avoid species-killing event long enough for significant numbers of us to get off this rock, our species could survive. That is, if we don't nuke ourselves first.
It doesn’t seem like those cities have any way to produce food underground without inputs from outside, so no, these would not be examples of self-sufficient underground civilizations.
Really cool though, like something out of Dwarf Fortress. I’d never heard of these so thanks for sharing.
Well yeah, but if we're talking about a post-collapse society where environmental destruction and starvation-driven civil chaos has wreaked havoc on our infrastructure and all resources that can be easily accessed have been mined out, how many things are they going to be putting into orbit?
I’m glad so many people are pessimistic because then I know I can do my best for humanity for myself and my loved and close ones.
Why do it for the masses who are ungrateful and only complain instead of trying to help? They’re welcome to come along for the ride, but they’ll always sit there and cry/complain/be annoying.
this doomerism is insane. look at the 20th century and what happend, yet we made it through. and you have some people thinking somehow life is worse and its actually going downhill? life is better than it has ever been. the only way humanity will not make it is if doomers keep pushing their dumb worldview and treating it as fact that the world is worse than its ever been, thus refusing to fix any problems. maybe go read a history book
Many of those futuristic space defense systems will also double as offensive weapons with terrific ability to do damage to the Earth. Ask yourself whether we're safer in a world where random asteroids are the threat, or one where human beings wielding random asteroids are the threat.
This reminds me of the sci-fi aphorism that any space drive powerful enough to be interesting doubles as a weapon of mass destruction. Similarly, so is anything powerful enough to deflect an asteroid which is a danger to the Earth.
So it's technically true, but do you really want to live in a world where we will never explore space or pursue technology that could one day save the species because we're afraid of what the worst of us might do with it? Sounds awfully depressing to me. Might as well consign the rest of humanity to grubbing plants out of the earth for all eternity. I'd prefer to see us blow ourselves to bits with some crazy futuristic technology than have no hope for our future besides running around in fields until the expanding Sun destroys the planet, which we'd have no hope of being able to deal with.
You could take that perspective on every major technological advancement, and yet we undeniably live in a safer, more comfortable world than before those advancements.
The chance of total destruction has always been the case for most of human history. Prior to our current abilities to predict the weather and mobilize aid internationally, floods, hurricanes, etc, hell, even just particularly heavy rains were all relatively unpredictable existential threats. Sure those weren't the end of the literal world, but they were the end of the world to people affected.
This article seems to be a fine example of "perfect is the enemy of good." Could boulders from an asteroid be dangerous? Sure! Would the asteroid they came from be more dangerous? Oh hell yeah.
This is like complaining because when a missile or drone was shot down the debris landed on a car. Basic physics says in any kind of energetic collision there's going to be debris, and basic statistics says that some of that debris has a chance of hitting something that we'd prefer not be damaged. Such is life.
I read these numbers in a profoundly different way from the article.
Based on these results, it looks feasible to divert the main mass of a potential impactor. That appears to run the unsurprising risk of ejecta that would themselves impact.
But this just means that the first impact decreases the problem measured in energy by (roughly) four orders of magnitude. This is because the ejected masses are much, much smaller than the original mass and because most of the ejected masses won't impact.
Nothing prevents applying the same technique to a few selected ejected masses. If the ratios apply again, we can decrease the thread by another four orders of magnitude. This is enough to reduce the KT impactor to a level that will burn in the atmosphere.
> ... the collision also shook off 37 boulders, each measuring from 3 to 22 feet across. None of the boulders is on a course to hit Earth, but if rubble from a future asteroid deflection were to reach our planet, Jewitt said, they’d hit at the same speed the asteroid was traveling — fast enough to cause tremendous damage.
Holy hell! OK -- do they burn up on entry? What's the criteria for that?
It's complicated. Depends on the cross-sectional area and the materials the boulders are made of. Ice, for example, burns up (melts) on reentry much more readily than iron!
Also depends on the angle of attack. Heading straight down (perpendicular to the ground beneath it) passes through much less atmosphere than a glancing blow, so has a lot less time to burn up.
I wonder how often perpendicular to the ground impacts occur? I seems that they could only occur if an asteroid approached in a head on collision with our orbit or perpendicular from a higher or lower orbit as it passes or is passed by the earth. That makes it statistically unlikely, doesn't it?
The statistical likelihood depends entirely on the timeframe. Within our lifetimes? Extremely unlikely for any large impact. Over the next billion years? A lot more likely!
Yeah if there's some solid iron asteroid out there heading right for us we're totally screwed. That's like a core of a planetessimal! Very dense stuff!
It could also be some lighter rock (a matrix) with iron clasts, created from a collision between a huge, light asteroid and smaller iron planetessimal fragments. Then if our planetary defense system breaks off a bunch of boulders, some could contain the heavy iron fragments and some might not, so different things would happen on reentry for each boulder.
> going to be extremely difficult to deflect due to the momentum
Momentum is a function of mass and velocity. The momentum of two similarly-massive asteroids, one rock the other metal, is the same. Given existing technologies, deflecting a solid-ish body is easier than a loose pile of gravel.
The average distance between asteroids (and their nearest neighbours) in the asteroid belt is about 8 times the earth-moon distance. Most of these asteroids have roughly the same orbit, so they have almost no relative velocity. So to achieve a collision we have to dramatically change the velocity of one of them in order to hit the other in a reasonable time frame.
But this doesn’t take into account the masses. Asteroids vary in size from about 1 metre across to the dwarf planet Ceres, at 1000 km across. A giant asteroid is unlikely to have other giant asteroids nearby. If one giant asteroid is on a collision course with earth, what is the likelihood we’ll find a similar-enough sized one within a reasonable enough distance to be able to make them collide? Extremely remote.
The point is composition has no influence on momentum. Nobody doubts causing two bullets, already mid-flight, to collide by shooting other bullets at them is nontrivial. To the degree I have seen it discussed, it’s in using a dense asteroid to gravitationally perturb a loose one. Precisely because dense, metallic asteroids’ orbits are easier for us to manipulate than rubble piles’.
> Space rocks smaller than about 25 meters (about 82 feet) will most likely burn up as they enter the Earth's atmosphere and cause little or no damage.
To/dr the small ones probably will, but it depends on the angle of approach, their composition, their speed, and even their shape and internal structure.
I've known of the risk of blowing an asteroid up into a swarm that's potentially more dangerous already for years, how is this unexpected according to the article?
The word 'unexpected' doesn't appear in the article. It's a fairly safe bet that the team of people capable of hitting a 581 foot object 6 million miles away with a 13,000 mph slug would have expected the ejection of material from the impact.
You're right, I interpreted "unintended" as "unexpected", because I assumed that if you know this before you do this then you know what to expect, so it must also be intended.
Certainly, but to the person who wrote the sub-heading (I suspect an editor rather than the article's author), it presents a "previously unanticipated risk." The further you get from the source...
It says "Smaller rocks flying off into space could create their own problems" so that's potentially more dangerous, maybe not likely, but still potentially :)
I don't think it's more dangerous it would just require more resources to counter. I mean day you have a3 like rock that splinters into 3x 1 mile rocks. I'm pretty sure we'll still have a bad day, especially with three impact sites but the magnitude of each impact will be less than the full impact of the fully intact 3 mile rock. Doing something is always better than nothing especially if we are facing extinction.
If only to say at least we tried. it's kind of amazing we actually live in an era where we can try. I mean it's only like 60 years of is being able to send rockets into space, we made it this long without needing to, but Knowing we can at least have a fighting chance is comforting.
Of course to win at this we also need to be able to detect in an early enough manner any and all disruptive size asteroids. it would suck too have the technology to save earth but not see our annihilation coming until it was too late to do anything.
It is absolutely amazing that deflecting an asteroid is something we can even test. Depending on the size of the flung off boulders it may be preferable to the larger asteroid impacting. However, I suspect that when a potential impactor is considered for deflection it will be big enough that cast off pieces could still pose a threat.
Due to the chaotic nature of orbital mechanics, small changes in initial conditions become large observable differences in behavior over time. It's also helpful that there is essentially no turbulence in space so every observation over time results in more and more precise estimates for the true orbital parameters of the body under observation.
If the size of the flung-off objects is proportional to the size of the asteroid that may be the case, but it's also possible it's mainly proportional to the force of the deflecting impact. Regardless between a potential extinction-level impact and hundreds, even thousands, of smaller, "Hiroshima-sized" impacts, the latter would still be massively preferable. Statistically the majority would hit the ocean and do little to nothing as well.
> Depending on the size of the flung off boulders it may be preferable to the larger asteroid impacting.
In nearly all cases, breaking an earth impacting asteroid into smaller pieces, many of which will burn up or have less bad impacts, is better unless of course the asteroid would have missed the Earth but some of the smaller pieces hit.
My guess is that the rapidly-expanding vapor and debris cloud produced by the explosion is likely to dislodge and eject more material than would result from a passive impactor capable of producing the same deflection. To get the same deflection, you need the same impulse, and in both cases, the impulse is applied as a sudden shock, but if you are using a passive impactor, all the energy is directed in the direction you want the change of the asteroid's momentum to be - so you need less energy overall?
does a nuke do the same damage in space, in a vacuum, with zero gravity, and no oxygen and other factors? would it do anything to a rock that's essentially as dense as earths core adjusting for size?
I think it'd be a cool test for them to do though.
I always wonder how you do the risk calculus for this kind of scenario.
Clearly if the certainty of a world-ending impact is 100% then committing the entirety of humanities resources to deflecting it would be justified and expected.
Regarding the atomic bomb factoid, they might have usefully added that 10,000 times that much energy reaches the Earth in the form of sunlight every second. (sunlight per second = 1.2e17 joules; the Hiroshima bomb = 1.5e13 joules.)
The problem with this plan is that most asteroids aren’t a giant chunk of rock, they are a collection of small rocks tenuously held together by feeble gravity, with maybe a few larger chunks inside that could be a danger to the planet.
Detecting the objects is the hard part. The planet killers are all likely to be highly elliptical objects with large orbital periods (on the order of thousands of years). With that kind of orbital period, we'd be lucky to see it before it has impacted.
Planets, by definition, have cleared their orbits around their respective star. So a planet killer threatening earth cannot share the earths orbit, or earth wouldn't be a planet. So a circular orbit shared with the earth is ruled out. But if it had a circular orbit that did not intersect the earths orbit, then there would be no chance of it hitting earth, so not really a planet killer either. The possible orbits that remain must be elliptical.
Now if a planet killer passed us every year then we probably would have hit them by now (or provided a gravity slingshot to alter its orbit!), so it follows that it must have a large orbital period :p
Notice that the object with an eccentricity of 0.8 has a much faster speed as it approaches the mass it is orbiting. So, to extrapolate, objects with a high eccentricity will be moving much faster as their semi major axis decreases (as they get closer to the mass it is orbiting). Faster means less time to detect the object. Less time to detect the object means we have less time to react to the object. Less time means planet killer.
And keep in mind the time periods we're talking about for some of these objects measure in the tens of thousands of years. So we don't really get a chance to record these objects for "next time".
You'd see more energy, but no more momentum transfer. Unless one of two things happened:
1. The nuclear warhead sent the back part of the rocket backward (that is, away from the asteroid) hard enough that (with respect to the asteroid) it has negative momentum, so that the part that hits the asteroid has more momentum.
2. The energy of the radiation from the warhead ablades material from the asteroid, turning it momentarily into a rocket motor. The momentum of that material leaving the asteroid causes an equal momentum change on the asteroid itself.
The momentum of the whole system would likely be similar, but it'd be spread over a much wider debris field - in the case of an asteroid impact, a field probably large enough that much of it would completely bypass instead of impacting.
From a practical standpoint, anyone debating between nuclear and non-nuclear options would probably have to look at the risks of a more complex projectile (reliability), whether an explosion would allow use of a smaller projectile (energy cost for getting there, terminal speed, accuracy at various speeds), and of course regulatory concerns with launching nuclear vs kinetic impactors.
How the hell was this unanticipated? You think ramming things into asteroids is not going to create any debris? I thought NASA was full of smart people.
The scientists had known for a long time that this was a possibility. That's part of the reason why the Dimorphos / Didymos asteroids were selected, their current orbit (even if altered a little) and any debris generated will never come close to Earth.
It is an asteroid redirect test. It has not been done before, so it is normal that unexpected consequences happen. It is very difficult to even get high resolution pictures of asteroids.
Studying the boulder swarm - amazing! Saying the boulders that came off are like shrapnel from a hand grenade - sure. Observing that the boulders keep the relative velocity of the original body and that they could cause damage if they hit something... ok yeah? Interplanetary velocities are energetic - true - and that this is similar to the energy of the Hiroshima atomic bomb - technically true also, but this is where it veers into sensationalism.
It's rather telling that this part is put as "Jewitt said" but not quoted. This could very mean that Jewitt said it would have X amount of energy, and the author decided to put in the nuclear bomb angle because it was a similar energy.
Asteroids this size just burn up. "In theory" they could hit something in orbit but space is mind-bogglingly huge and this is exceedingly unlikely. And weighed against surface impact of something judged worthy of a planetary defense scenario?
Unanticipated risks?