Planetary defense test deflected an asteroid but unleashed a boulder swarm
newsroom.ucla.edu
newsroom.ucla.edu
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?
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.
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.
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.
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.
> 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.
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.
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.
https://www.nasa.gov/mission_pages/asteroids/overview/fastfa...
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...
That was cool, thanks.
I enjoy the traces of whimsical-not-evil old Google that still resurface every now and then.
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.
This is observational evidence regarding the swarm. Not anyone expressing incredulity at a collision producing ejecta.
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.
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.
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.
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.
It would be extremely unlikely.
10,000 spread over the planet--extinction.
As for people dumb enough to make the weapons in large numbers (https://www.businessinsider.com/putin-doomsday-status-6-nucl...)
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.
Really cool though, like something out of Dwarf Fortress. I’d never heard of these so thanks for sharing.
More likely we never make it there because of a host of other, more boring reasons, mostly; we won't need anything like it.
Who, exactly are we defending ourselves against? A once-in-a-million-years impact that this very test showed we have a conceptual means of resolving?
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.
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.
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.
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.
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.
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.
Isn’t this among the easier to deflect? You literally smash other asteroids into it without much fear of it breaking up.
As for smashing “other asteroids” into it, that’s likely not feasible due to the vast distances between asteroids and the masses involved.
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.
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.
https://www.nasa.gov/mission_pages/asteroids/overview/fastfa...
I'll say you're a scammer. I'm willing to sell it for half the price. Comes with a certificate demarcating the plot as well.
NASA knew there would be rubble put into orbit around the asteroid.
The idiot author of the article has embarrassed himself, his company, his industry, and his advertisers by thinking orbiting ejecta was "unexpected."
For starters, that is not what is suggested.
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.
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.
I think it'd be a cool test for them to do though.
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.
But what about if the the certainty is 90%? 80%?
What does "committing the entirety of humanities resources" even look like? Anyway, this is certainly something that will never happen.
But committing a lot of resources, yes, we'll do that if it's 1% too.
Surely slamming an asteroid with a fast moving mass (or explosive weaponry, etc) is expected to knock chunks off it?
That has to be the most logical, obvious-as-all-hell result yeah?
It will require identifying them when they are far off. Ramming into them will be plan B!
Not saying you're wrong, but... what is your basis for claiming that this is true?
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
But to more fully answer the question look to https://en.m.wikipedia.org/wiki/Elliptic_orbit
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".
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.
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.