A 2022 NASA mission changed the orbit of the asteroid Dimorphos around its companion. New data shows their joint orbit around the sun also changed.
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Wild that we went from "can we even deflect an asteroid" to measurably changing a solar orbit. 150 milliseconds sounds tiny until you realize compounding over decades makes that a meaningful trajectory shift. The engineering confidence this gives for actual planetary defense is massive.
> The engineering confidence this gives for actual planetary defense is massive.
Is it? Isn’t it the case that we can’t even detect the vast majority of objects on a potentially problematic intersection path with earth? I feel like the most likely scenario is that by the time we realize we’re about to get slammed by an asteroid, it’s way too late.
Two different problems: detection, deflection.
Before this, even if we spotted one, we didn’t know if we could prevent impact.
Detection honestly feels like an easier problem, especially as networked sensors and space-lift capacity has improved.
Is there really better confidence we could now detect a similar 2013 Chelyabinsk meteor event?
By alex43578 2026-03-133:02 Yes? Rubin is supposed to contribute, and more broadly we have more and better "eyes" on the night's sky than ever before. There's always the opportunity for more tracking, but tracking without being able to do anything about it would've been pointless.
By gatreddi 2026-03-133:16 Detection is still the weak link, that part is true. But the equation is shifting. Surveys like NASA’s NEOWISE mission and the upcoming NEO Surveyor mission are specifically aimed at finding those missing near-Earth objects earlier.
The point of DART mission wasn’t that we can deflect every asteroid tomorrow. It was to prove that physics and guidance actually work in space. Now the playbook is clearer: detect earlier, then nudge early.
If you get even a few years of warning, a tiny velocity change compounds into a huge miss distance. That’s the real takeaway.
By phkahler 2026-03-1213:44 >> The engineering confidence this gives for actual planetary defense is massive.
I've been waiting for this a long time. They initially reported significant changes to the orbit of the smaller rock around the larger one which was cool and all, but I kept wanting to hear how much it affected the whole system. I suspect it's taken several years to answer that because it's such a tiny change in velocity. Dimorphos we can deflect, Didymos not so much.
By ivanjermakov 2026-03-1217:392 reply I find it mesmerizing how predictable orbital mechanics are. We can tell where celestial body will be years ahead with meter accuracy.
I think that’s what makes the 3 body problem unintuitive, given how we can predict 2 easily.
By littlestymaar 2026-03-133:38 There's no “two body problem” here, the solar system is an n-body problem.
And the “three-body problem” is overblown in pop culture: even n-body problems are fairly predictable in the short-ish term, it's just that you cannot predict things over a long period because measurement imprecisions have a snowball effect, but it's not particularly unintuitive (I'd say it's more intuitive than the idea that we could predict things with perfect precision over billions of years).
By mkbosmans 2026-03-137:41 Well, the article says that the effect of the impact was much larger than the scientists expected. That doesn't really give a lot of confidence in how good we are at predicting these things.
By nacozarina 2026-03-1219:49 Makes you wonder how many other objects were sent on new trajectories by even smaller influences
You know what they say: the best planetary offense is a good asteroid redirect program
It's also the best planetary terrorism, going by the plot of The Expanse
It only worked in the Expanse because they expertly choose a special trajectory that made the rocks hard to detect and some questionable (but plot necessary) "stealth coating".
By this point UN and MCR have been in cold war for 100+ years staring each other down with region killer nuke arsenals and an absurd amount of interceptors always ready. See than one time Mars actually fired a barrage - only like two warheads got through, only due to shitload of decoys and overall numbers.
A dumb rock would totally get vaporized without the plot armor in a safe distance.
Ok. The Expanse is a show/book - that doesn't actually portray any of this very well, but its very important to note - there are no satellites in orbit, with nukes or any kind of missiles - if you want to pretend they are, they are most definitely pointed at the earth.
I'd love to buy into that plot armor but there is too much to take seriously by S6. The reality is, the first time a colony decided to it was independent enough, to use an asteroid - they would pick one, or many, so as to to render earth uninhabitable, there is no doing what they did in the show - thats how you lose a war AFTER having already used a weapon of last resort.
Once Inoki or w/e his name decided to use an asteroid, and one hits, the ONLY choice open to Earth is an immediate unconditional surrender. The only correct choice for asteroid #2 is one that will end all life on the planet without any doubt.
What's her name? The President would have killed us all and attained nothing doing so.
By m4rtink 2026-03-1311:31 I think given the technology that has been shown - a massive space and planetary infrastructure base, torpedoes with torch drives armed with nukes that would make Teller blush - I don't think you can actually use Dinosaur killer asteroid unnoticed.
That would be far too big to not be spotted by the many UN aligned sensor platforms all around Sol, well before it is actually on a collision course as changing the trajectory of something this massive could take a long time, not to mention for it to actually travel all the way to Earth on that trajectory.
I am sure that Belter Cheguevara was not the first one to get these ideas, so any major power not tracking most asteroid orbits in almost real time at this point would be stupid. The technology they demonstrated to have should easily allow that.
And by that point one of the many Ships UN has all around the system would just go there and shoot anyone working on the big rock to pieces. Possibly deploying tugs to change the trajectory to a safe one afterwards.
So I think they had to use rock small enough not to be easily tracked, that could be quickly accelerated + that special stealth coating from the Martians. Enough to kill a city and devastate a region but not much else.
First things first, we have to colonize the rest of the solar system before we can terrorize Earth.
By dylan604 2026-03-1214:30 That totally depends on the type of super villain organization we're discussing. Some are willing to watch the Earth burn making the colonization step unnecessary. Others think humans are the problem and again would be willing to skip that step.
By vova_hn2 2026-03-1215:50 It depends on the size of the asteroid and precision with which it can be aimed...
By MisterTea 2026-03-1222:09 > before we can terrorize Earth.
Before?! We're already doing a great job at it!
Why exactly? I think the US ought to spend a few trillion on an actual space battleship - one that never comes down to the surface, just sits in orbit. There was a project regarding dropping telephone pole sized pieces of metal from space as an offensive weapon - put something like that on the space battleship and...
That is simply "Assured Destruction" with absolutely no mutual drawbacks or lingering consequences like radioactive wasteland. Just craters.
This is also something where the 1st country to achieve the "Space Battleship" could effectively prevent any other from also doing so...
In theory, Bezos or Musk could do it.
I don't understand why any country would bother with ground based military assets at this point.
> That is simply "Assured Destruction" with absolutely no mutual drawbacks
Nuclear countries would simply declare that they will launch nukes if any rod comes down on their territory. Even if you had thousands of projectiles in orbit (at considerable cost per projectile) this would not be significantly different from 60s-style MAD: put nukes in bunkers, in the air and in the sea to ensure they can't all be taken out. We might see the return of strategic bombers that stays in the air for weeks at a time.
Alternatively they can just shoot down your battleship with anti-satellite weapons. The risk of retaliation might be worth preventing the disadvantaged position in the long term
That reaction is not the same tho - a rod isn't even a conventional weapon, I am not certain off hand that an incredibly destructive such weapon would even be banned under current treaties. That matters bc your taking about the end of the world. Only Russia would ever shoot at the US - so, dont drop rods on Russia.
Plus - if countries don't do space wars - this will still happen 100%. It will just be a non-state actor - who do you nuke if Austin Powers is the bad guy from space?
Also, there seems to be a prevailing sense of "we'll just shoot it down" and that is actually extraordinarily unlikely - bc of all the space, in space. I wouldn't sit in orbit with my Space Battleship - maybe a lunar orbit.
Let's say I park halfway to the moon - ALL of my missiles will still hit earth, I don't think current defense systems would have any better odds - whats the difference between an ICBM that enters the atmosphere from space - shot from a silo or a spaceship?? Not much, functionally identical to the Space Battleship... missiles from earth tho, will be like in slow motion, the space battleship ought to be able to literally shoot them down with bullets - none will be able to surprise the space battleship, how do you even do a missle defense overwhelm tactic in such a situation - I can move the spaceship you know.
I may sound like I'm being unserious, but in reality, this is absolutely the future of warfare 100% - I can't be more serious, the humor is bc this topic makes me legitimately nervous.
Heinlein's The Moon Is A Harsh Mistress kind of mapped out what to expect if/when your adversary manages to position themselves significantly above you in the Earth's gravity well.
By Ajakks 2026-03-133:39 What an incredibly foresightful work - I have not read that, I will tho. Thanks!
And yeah, it is perhaps the most extremely imbalanced strategic advantage that can be attained.
You've described a space station, which three countries have already done independently (Mir, SkyLab, Tiangong).
But dropping rods from an orbiting platform makes no sense. There's a reason that "Rods from God" didn't pan out, and it has to do with orbital dynamics. Neither Bezos nor Musk can do it, because it actually doesn't work.
I doubt it was seriously considered at the time it was discussed. Space Stations are in orbit - the space battleship doesn't have to be, that is very significant.
Earth is spinning in a giant circle around the sun. Thats facts. "aiming an asteroid" is less of making a rock a missile - and a lot more of tug-boating it into the exact right spot, in the way of earth, so that earth hits the asteroid - not anything complicated like the asteroid hitting earth.
There are a lot of little things like that...
By m4rtink 2026-03-1223:26 Any realistic space warship design will need propellant - sure you can avoid ground based interceptors and kill sats but it will eat into your propellant reserves over time.
You will need to replenish from somewhere & that somewhere might as well get nuked instead of the ship, rendering it useless.
> Space Stations are in orbit - the space battleship doesn't have to be
I mean, you did say:
> space battleship - one that never comes down to the surface, just sits in orbit.
So I think it's understandable for people to take that at face value.
Furthermore, if it isn't in orbit, then where would it be?
> and a lot more of tug-boating it into the exact right spot, in the way of earth, so that earth hits the asteroid - not anything complicated like the asteroid hitting earth.
From an orbital mechanics standpoint I don't think there's actually a difference. You're changing an orbit either way.
If I were holding earth hostage with my Space Battleship - I would sit in a lunar orbit. Also, I am not kidding about tug-boating - if I fly up, match an asteroids speed and velocity, why cant I just throw a tow strap on that, accelerate, and park it an area that only has to be accurate enough for a planet to hit it - I dont need to stop it, or have it flying at the earth, it only needs to be in the way, moving a little slower than the earth.
What if I make that the space battleship's job? What if a drone can do that?
Im not really worried about resupplying the space battleship holding earth hostage -> someone will "volunteer" to do that, bc they want to live life.
> I would sit in a lunar orbit
Ah, so by "orbit" you were talking about orbit around Earth specifically?
> why cant I just throw a tow strap on that, accelerate, and park it an area that only has to be accurate enough for a planet to hit it - I dont need to stop it, or have it flying at the earth, it only needs to be in the way, moving a little slower than the earth.
Again, from a high-level orbital mechanics perspective there is little difference between the two. You start with two non-intersecting orbits and you're changing one orbit to intersect the other at the same time and place. How you go about doing so is just a question of how much time/fuel you're willing to expend, for various values of "just".
That being said, assuming I'm interpreting you correctly what you propose is probably technically possible (e.g., change an asteroid's orbit to a slightly-larger-than-Earth-sized one), but it's also very fuel-intensive compared to skipping the "parking"/"in the way" part.
If you haven't tried it already I can't recommend Kerbal Space Program enough for experimenting with this kind of thing, especially if you are alright with playing with mods. Real Solar System (changes the in-game solar system to match the our real-life one) and Principia (replaces the simplified patched conics system KSP uses for orbits with n-body gravity) would be particularly relevant here.
I absolutely will check out Kerbal - I have done nothing more than thought experiments - which I'm sure is obvious, its obvious to me. I'm sure I am saying things exactly wrong - the idea is to save fuel and remove all of the difficulties that may arise with timing or aiming. Using more fuel is exactly opposite intent.
I may be confused but I dont mean a "larger orbit than the earth" -> I mean the exact identical orbit, the exact path that earth takes around the sun -> ahead (or behind, it does not matter) of where we are and instead of 365 days to circle the sun, the asteroid is moving at a rate that will take MORE days -> so the earth will smash into the asteroid, bc it can't do anything else. I dont mean "park" in the sense that I stop its movement, nor would I select an asteroid that has such an orbit that it couldn't be manipulated into position with little difficulty.
Like, imagine the solar system was a record on record player (I've never used one either) and the earth is on a line/groove - a choice asteroid is moving in the same direction on an immediately adjacent line/groove - the asteroid only needs to move onto the earth's groove (anywhere on that specific groove the earth occupies on the record works) and then the asteroid is then sped up or slowed down (not much tho) on that exact orbit -> either will result in a collision with earth.
The only real way to stop such activities is with spaceships. That is my entire argument - you are saying that is less feasible than making a missle out of an asteroid? I appreciate the explanation fr
Tbh, it wasn't until the game Terra Invicta that I really considered the solar system, as it actually is. That game has no other relevance to this particular conversation - good game, very different kind of 4x that I recommend but unrelated.
By aw1621107 2026-03-136:54 > I mean the exact identical orbit, the exact path that earth takes around the sun -> ahead (or behind, it does not matter) of where we are and instead of 365 days to circle the sun, the asteroid is moving at a rate that will take MORE days
Unfortunately that's not really possible. To a first approximation, Earth's orbit is a circle with the Sun at its center, and the size of that circle is determined entirely by Earth's orbital speed around the Sun. Assuming you're also in a circular orbit, if you move at Earth's speed, the size of your orbit will be the same as that of Earth's. If you move faster or slower, your orbit will be smaller or larger, respectively, unless you wish to continuously burn fuel to maintain your distance from the Sun. That's why I said the asteroid's orbit must be slightly larger than that of Earth's for an Earth-catches-up-to-asteroid-in-similar-orbit scenario.
Obviously things get more complicated once you consider non-circular orbits, but the end result is similar - you can't continuously hang out in Earth's path while moving slower than the Earth around the Sun without burning a stupendous amount of fuel.
> you are saying that is less feasible than making a missle out of an asteroid? I appreciate the explanation fr
I think it's more that I think that "making a missile" is likely to require less fuel since you only need to adjust the asteroid's orbit ~once (only need to get it on a collision course) instead of ~twice (get the asteroid on a near-collision course, then adjust it again for the "right" kind of collision).
I cant reply to your other comment - that is what I assumed you were saying but it does not make sense to me outside the process that naturally occurs - I'm assuming the suns gravity simply cant move objects of such different mass, at the same rate, and thereby the orbit and position changes accordingly?
The speed doesn't have to be much different - 366 days and earth will eventually hit asteroid - 364 days and it will eventually hit the earth.
Ahh, Im still having a hard time figuring out why that would take more energy - I'm going to be researching this all morning tomorrow.
Thanks for the help!
By aw1621107 2026-03-138:34 > I'm assuming the suns gravity simply cant move objects of such different mass, at the same rate, and thereby the orbit and position changes accordingly?
Kind of? An object moving in a circular motion at a constant speed must have an acceleration towards the center of the circle of (velocity^2)/(radius). This means that two objects in the same circular orbit moving at different speeds must be experiencing different accelerations towards the center of the circle.
In the simplified case of orbits around the Sun, that acceleration towards the center of the orbit is due to the Sun's gravity. However, gravity accelerates everything at a given distance at the same rate. As a result, you can't have two objects solely influenced by the Sun's gravity that orbit around the Sun with the same orbital shape but moving at different speeds. You'd need something in addition to the Sun's gravity to pull that off.
> The speed doesn't have to be much different - 366 days and earth will eventually hit asteroid - 364 days and it will eventually hit the earth.
Sure. When I said slightly-larger-than-Earth-sized orbit, I really meant it. Kepler's third law of planetary motion states (approximately) that (orbital period)^2 is proportional to (radius)^3. Assuming I did my math correctly, if your orbital period goes from 365 to 366 days your orbital radius gets ~0.18% larger, which is roughly 274000 km increase over the radius of Earth's orbit. That would fit inside the Moon's orbit (~385000 km from the Earth)!
> Ahh, Im still having a hard time figuring out why that would take more energy
At least the way I was thinking, the short answer is that one alteration to an orbit is likely to be cheaper than two, especially if you aren't particularly concerned in what manner the asteroid eventually collides with Earth.
By ryan_j_naughton 2026-03-1222:26 > There's a reason that "Rods from God" didn't pan out, and it has to do with orbital dynamics. Neither Bezos nor Musk can do it, because it actually doesn't work.
Can you say more on this? Thanks!
By MisterTea 2026-03-1222:15 > . There was a project regarding dropping telephone pole sized pieces of metal from space as an offensive weapon
I remember it was nicknamed "Rods From God". Kinetic energy weapon using 9 ton tungsten rods dropped from an orbiting platform. https://en.wikipedia.org/wiki/Kinetic_bombardment
The technology doesn't exist and it would be a huge waste of money.
How heavy would a telephone pole sized tungsten rod be?
What happens when China, Russia, India or Pakistan find out you are building this (cause you can't hide it if it's in near earth orbit)? They would either knock it out of the sky or hit you with everything they have. We would do the exact same if anyone else was developing such a weapon.
I personally would get whatever metal in space, so weight is not the issue - solving this problem would also create almost immediately chunks of rocks that could also be dropped. In all reality, anything can be "setup" to be a weapon - many ways have been identified here.
All required innovations - of which, most are not out of reach in the slightest, all of that tech would be immensely valuable, literally everything we do to secure space superiority will be actual gains - not smaller microchips equivalent innovations - entirely new machines, entirely new economies of scale - there is no equivalent military tech that we can develop on earth.
Not only is there really no conceivable way to ignore the strategic advantage once considered, the long-term economic payoff is actually reason enough alone to pursue the radical idea of a "space battleship" - I can think of about 20 ways to cause significant global issues with one measly space battleship.
As a hypothetical alone, it has reason enough to warrant a substantial amount of the 1.5 trillion defense budget the Pentagon plays with.
If this is satire, it's not that funny. If you're serious, it's a good example of 'the ugly American.'
By Ajakks 2026-03-132:58 I wish it were satire - we do actually need to have space defenses, asteroids exist 2st off - its just bc we ignore all the craters that we sleep at night.
We feel safe here on earth but it's really a giant graveyard trap - that so effectively exerts control over life on it, that it made all living mammals out of mice - we may actually be safer on almost any other planet.
All life on earth has eventually died out so far, we are the 1st species that could stop the most likely extinction level event - but this DART is the closest we ever got to actually taking up that responsibility - the preservation of our species and whatnot, thats just 1 minor reason.
The most important tho, given how much we have example of people "getting theirs" at all other peoples expense - this is much worse if a non-state actor gets there 1st.
Lastly, I do have to clarify the American position - we run the world, or there will not be one to run. Nobody alive today made that decision - it changes nothing, once that choice was made, we are locked into it. Did you think we are only an economic power? That is the front. We can always pivot to actual power - the kind that can destroy all cities above a certain size - we have never hid this fact, the whole world knows of MAD. That is what power is.
What is American power if someone can destroy the US and we can't destroy them?? That doesn't work for the US - nothing at all changes if the US gets that spaceship first.
You can call this ugly - there were more modern wars before we started running things, from the looks of things - the whole world will go to war the moment we are out of the picture.
By m4rtink 2026-03-1223:22 The story of Footfall is basically about that - and alien space invasion force with torch drive powered space battleship in orbit.
There are ways to battle that - balistic missile submarines for one and then "Project Michael" which would be a massive spoiler to elaborate on. ;-)
By ge96 2026-03-1214:51 queue the neurodivergent mech pilot
Slight changes can cause such impacts? Now imagine how many other meteors and comets also will be adjusting because of this. Will one of them once on a course to never hit earth suddenly shift to hit earth in a thousand years time? The confidence i get is the opposite
I don't think asteroids (like the target) have influence on others. There's so much space between them, and their mass is almost neglible.
By nashashmi 2026-03-1222:07 Oh no. I was not talking about the other objects that float through space influenced by such a small object so far away.
I was talking about the sun shaking in its orbit because high velocity objects are now pulling at it differently causing other objects to be influenced by the new position of the sun.
I read the parent comment as “solar orbit change” meaning the sub was changing position.
By infinitewars 2026-03-1214:553 reply > slowed the orbit of a pair of asteroids around the sun by more than 10 micrometers per second
Or in other words, 1 meter per day
Why not say that?
Because the SI unit is meters per second, so maintaining the “second” gives people with that understanding a basis in which to compare the delta-V.
By rkagerer 2026-03-1221:33 I'm genuinely curious whether there are a substantial number of people out there who deal on a regular basis with dV's on such a minute scale. Who would that be, outside an asteriod-redirect program such as this? Satellite operators doing precision trajectory correction?
I found the meter per day conversion helpful. Through another lens, it's about 0.000036 km/hour (or about 1.5 inches per hour).
Okay but they didn't give it in meters per second, they gave it in micrometers per second. Converting to micrometers per second is exactly as much arithmetic as converting to meters per day.
No, it is not. It is in fact no arithmetic at all, if you understand how SI works.
Yes, it's one multiplication in both cases.
Multiplying/dividing by 1 million is way easier than by 86400 though.
By jjk166 2026-03-1519:09 I would argue that multiplying 10 by 86400 is just as easy as multiplying 10 by any other number. Hint, it's the same as multiplying a number by 10.
By cheschire 2026-03-1221:20 One would think that any nerds that knowledgeable could divide by 86400 to make the article more accessible for the rest of us though.
By stronglikedan 2026-03-1215:13 1.22337962962963e-21 light years per second!
By infinitewars 2026-03-133:16 1 meter per day is something most people can understand. But even more relevant would be 1 Earth diameter in 16,000 years... which makes it very clear this isn't useful for saving the Earth from asteroids yet.
Interesting. I'd not considered the loss of mass as a means of propulsion.
Obviously there was the kinetic energy transfer but the impact ejacted some of the asteroids mass opposite to it's trajectory further increasing it's trajectory change.
Cool demonstration, hopefully not needed one day.
By dylan604 2026-03-1214:35 When the impact happened the news articles seemed to imply some surprise about that as well which seemed strange to me. I just wrote it off to the journalist just not being up to speed on the subject matter. The size of the debris field trailing also seemed to be a surprising result.
By alhirzel 2026-03-1213:29 It's the butterfly effect. After the momentum exchange (the rocket slamming, stuff being ejected in the impact, etc), the entire system was left with different properties. From now on, the equation F=Gm1m2/r^2 will have a different m1, and you can sum the equation over all m2 (literally every other massive object in the universe).
Yeah, I sort of meant in the context of an object losing its mass, it's seldom used on earth as the effects are small but on the timescale/distance/speeds of an asteroid it could have noticeable effects.
Rockets are using mass loss but there's more going on with the rapidly expanding gas causing the increased impulse.
By fc417fc802 2026-03-1211:22 Rockets are able to optimize due to dealing with a gas. It's still just pushing off of a disconnected mass. You go one way the lost mass goes the other.
If you think about it that's how a cannon works. The projectile gets pushed forwards and the barrel gets pushed in the opposite direction. Some of the larger ones can push their launcher back quite a bit more than you might expect.
My point is that this is actually a common failure of intuition. We tend to think of larger objects on earth as fixed and in our day to day life on dry land they often are (at least more or less) due to static friction.
A slightly more interesting observation (I think) is that if the bodies don't achieve escape velocity relative to one another then the forces all cancel out in the end. It just might take an arbitrarily long time in the case of similarly sized masses.
