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We often hear in science fiction that if an asteroid were to come barreling towards earth, we could somehow either change it's trajectory or break it up into mu

We often hear in science fiction that if an asteroid were to come barreling towards earth, we could somehow either change it's trajectory or break it up into multiple pieces by shooting it with a ICBM/nuclear weapon/etc. What truth is there to this? Suppose this asteroid was on a collision course with earth, would we have any recourse other than praying it lands in Siberia and not NYC.

alex_duf 4y ago
At this sort of scale I don't think it makes a big difference that it hits Siberia, the middle of the Pacific, or wherever you're living. In fact maybe it's better to take it directly on your head.
- gcanyon 4y ago
  On the flip side, it's maybe 1/300th the size of the one that killed the dinosaurs. So, definitely not great, but survivable. (obviously with major death, destruction, and setback to humanity)
shagie 4y ago
> What truth is there to this? Suppose this asteroid was on a collision course with earth, would we have any recourse other than praying it lands in Siberia and not NYC. Astrodynamic Fundamentals for Deflecting Hazardous Near-Earth Objects - https://www.adrc.iastate.edu/files/2012/09/IAC-09.C1.3.1.pdf https://www.adrc.iastate.edu/files/2012/09/IAC-09.C1.3.1.pdf That paper goes into the what it would take to divert an asteroid (with emphasis on Apophis).
jjk166 4y ago
Depends on timing. ICBMs can only reach an altitude of about 1300km and are not designed to hit moving targets in space anyways, so if an asteroid is going to hit us in the next few days we're screwed. However implementing a system to defend against asteroids even with short notice is feasible. We can make rockets much larger than ICBMs and put them on standby for planetary defense. You'd presumably put appropriate sensors and maneuvering thrusters for getting to the approrpiate position near or on the target, akin to the interceptors used in missile defense. Interceptors would have a dedicated 3rd stage like the Centaur to launch them on trajectories away from Earth - the further away the interception the smaller the necessary deflection. Ideally you'd catch it early and start the deflection so far away that a kinetic impactor or even just the craft's gravitation would nudge it to a safe course, but for short notice you need to go nuclear. Breaking up an asteroid into smaller pieces with a nuke is possible, especially for the subset of asteroids which are basically loosely held together piles of gravel. Some people think this is a bad idea as instead of 1 big rock to deal with now you have lots of little rocks that are also radioactive, but that actually is a much preferable situation. The ability of objects to pass through the atmosphere is dependent on their diameter, lots of small rocks will burn up harmlessly while a single big one will impact. The radioactivity from the nuke would be spread out extremely dilute, and specific nuclear weapon designs which minimize neutron activation can keep the radioactivity very low. A more serious concern is that you don't know the trajectories of the resulting fragments, some of which might still be dangerous, and thus it would be a very bad idea to destroy it before impact was a certainty, but then waiting until the last minute to stop it is a major risk in itself. More safe would be to detonate the nuclear device near the asteroid. This would vaporize a thin layer of the surface of the asteroid in line of sight of the explosion, sending it flying off into space at extremely high velocity and propelling the asteroid equally in the opposite direction. There are two major advantages to this approach: it will work against targets regardless of their composition and internal structure (very beneficial if we don't have time to study the asteroid ahead of time) and the method can be done repeatedly to the same target - we could launch dozens of independent interceptors and just keep detonating them one by one until we get the desired result. While the goal is to have the asteroid not impact at all, and thus radioactivity is even less of a concern, this option does produce even less radioactivity than blowing up the asteroid. From a strictly technical perspective this option is pretty much a no brainer, but obviously building a battery of dozens of nuclear missiles is politically problematic.
- shagie 4y ago
  A sibling comment of mine references https://www.adrc.iastate.edu/files/2012/09/IAC-09.C1.3.1.pdf https://www.adrc.iastate.edu/files/2012/09/IAC-09.C1.3.1.pdf Section 6.1 is on nuclear stand off explosions. > The nuclear standoff explosions require an optimal standoff distance for a maximum velocity change of a target as- teroid. Therefore, we have to determine how close the nuclear explosion must be to effectively change the or- bital trajectories of asteroids of different types, sizes, and shapes. The precise outcome of a NEO deflection at- tempt using a nuclear standoff explosion is dependent on myriad variables. Shape and composition of the tar- get NEO are critical factors. Section 6.2 is on kinetic impacters... > A somewhat futuristic, solar sailing mission concept utilizing a 160-m solar sail to deliver a 150-kg kinetic impactor into a heliocentric retrograde orbit was studied in [25-28]. Such kinetic impactors will result in a head- on collision with a target asteroid at its perihelion (as illustrated in Fig. 1), thus increasing its impact velocity to at least 70 km/s. The NEAR Shoemaker study of as- teroid Mathilde and the Japanese Hayabusa mission for exploring the asteroid Itokawa suggest that many aster- oids are essentially “rubble piles.” Consequently, a practical concern of any impulsive approaches employing kinetic impactors or nuclear explosions is the risk that such high-energy deflection attempts could result in the frag- mentation of NEOs, which could substantially increase the damage upon Earth impact. And then, section 6.3 is a fun one: Gravitational Binding Energy > the disruption energy per unit asteroid mass is predicted to be 150 J/kg for strength-dominated asteroids. This indicates that a strength-dominated, 200-m asteroid would not be disrupted by a 150-kg impactor at a high impact velocity of 70 km/s. Also in Ref. 5 (pp. 135-136), the energy (per unit asteroid mass) required for both disruption and dispersion of a 1-km asteroid is predicted to be 5 kJ/kg. Thus, the feasibility of the most kinetic-impact approaches for either disrupting or deflecting an incoming NEO depends on its size and composition (e.g., solid body, porous rubble pile, etc.), as well as the time available to change its orbit. These are from 2012, and we've had a decade more experience (and a mission to try it out) since then... but it's interesting to look at and the math in the paper doesn't change.
- LargoLasskhyfv 4y ago
  Lots of small rocks can cause a 'heat pulse' over wide areas on atmospheric entry.
pif 4y ago
In order to change its trajectory, you need some wisely applied momentum, not a catastrophic explosion. The most powerful explosion may at most reduce the size of the biggest chunks, but not change the vector velocity of the barycentre at all.
- 0cf8612b2e1e 4y ago
  My completely naive take: if something is X AU away from the planet, why wouldn’t the tiniest course change result in missing the Earth by a huge margin? Even a fractional alteration of momentum in any off axis direction seems like it would have the desired effect. It feels like smashing any available rocket into the side of a non accelerating body would be effective, but space physics is weird, so I must be missing something.
  - pif 4y ago
    Your analysis is correct and wrong at the same time. You are not considering the fact that we currently are not able to observe a rock a few AC away with the precision that is necessary to assess that it is going to hit us, and that the gentle punch we can give it will not worsen the situation.
more_corn 4y ago
Blowing it up doesn’t work. Turns a cannonball into buck shot. Seeing it early is the ticket. A tiny thrust over a long period of time is the way to move things in space.
helloworld11 4y ago
>What truth is there to this? Suppose this asteroid was on a collision course with earth, would we have any recourse other than praying it lands in Siberia and not NYC. If your asteroid is only 20 to maybe 400 meters across, having it land somewhere absurdly remote on land or far off into the deep oceans would minimize harm, but for asteroids much bigger than that (and even 400 meters is really stretching the bounds of acceptable size), it doesn't really matter where the impact happens, millions or more people will almost certainly die. If you scale up to a size of, say, 900 meters or larger, then you're talking global multi-year catastrophe no matter where the impact is. If you then scale up to over a mile or two in diameter, then you're talking global multi-decade cataclysm no matter where the impact site is. So yeah, even with Siberia, the Canadian North, Antarctica, the Sahara or the central pacific ocean. Any size beyond a few hundred meters makes specifics not so important in terms of death toll and major climate effects.
__s 4y ago
NASA's recent DART project was testing this question The sooner the threat is detected the lighter the necessary response
Rebelgecko 4y ago
NASA's Dart mission yeeted itself into Dimorphos a few weeks ago to gather data that will hopefully help build a model of how much energy it takes to divert an asteroid.
yodon 4y ago
> praying it lands in Siberia and not NYC The Siberian Tunguska event was thought to be caused by a 20m diameter object hitting the earth. This is talking about a 900m diameter object which likely has 100,000x the mass of the object that hit Tunguska. EDIT (per comments below): 400,000x the Chelyabinsk object 27,000x the Tunguska object
- lloeki 4y ago
  > 900m diameter Article says it's 0.9mi, so 1.5km > 20m That was Chelyabinsk, Tunguska is thought to have been 50-60m
  - yodon 4y ago
    Interesting: Google's search snippet for 'how big was the tunguska meteor' found and reported a 20m size estimate from the Tunguska wikipedia page, but on manually reading the wikipedia page it becomes apparent that size estimate is for the Chelyabinsk meteor (which is also discussed on the the Tunguska wikipedia page).
Normille 4y ago
>...praying it lands in Siberia and not NYC. or vice versa.

alex_duf 4y ago

At this sort of scale I don't think it makes a big difference that it hits Siberia, the middle of the Pacific, or wherever you're living. In fact maybe it's better to take it directly on your head.

gcanyon 4y ago
On the flip side, it's maybe 1/300th the size of the one that killed the dinosaurs. So, definitely not great, but survivable. (obviously with major death, destruction, and setback to humanity)

shagie 4y ago

> What truth is there to this? Suppose this asteroid was on a collision course with earth, would we have any recourse other than praying it lands in Siberia and not NYC. Astrodynamic Fundamentals for Deflecting Hazardous Near-Earth Objects - https://www.adrc.iastate.edu/files/2012/09/IAC-09.C1.3.1.pdf https://www.adrc.iastate.edu/files/2012/09/IAC-09.C1.3.1.pdf That paper goes into the what it would take to divert an asteroid (with emphasis on Apophis).

jjk166 4y ago

Depends on timing. ICBMs can only reach an altitude of about 1300km and are not designed to hit moving targets in space anyways, so if an asteroid is going to hit us in the next few days we're screwed. However implementing a system to defend against asteroids even with short notice is feasible. We can make rockets much larger than ICBMs and put them on standby for planetary defense. You'd presumably put appropriate sensors and maneuvering thrusters for getting to the approrpiate position near or on the target, akin to the interceptors used in missile defense. Interceptors would have a dedicated 3rd stage like the Centaur to launch them on trajectories away from Earth - the further away the interception the smaller the necessary deflection. Ideally you'd catch it early and start the deflection so far away that a kinetic impactor or even just the craft's gravitation would nudge it to a safe course, but for short notice you need to go nuclear. Breaking up an asteroid into smaller pieces with a nuke is possible, especially for the subset of asteroids which are basically loosely held together piles of gravel. Some people think this is a bad idea as instead of 1 big rock to deal with now you have lots of little rocks that are also radioactive, but that actually is a much preferable situation. The ability of objects to pass through the atmosphere is dependent on their diameter, lots of small rocks will burn up harmlessly while a single big one will impact. The radioactivity from the nuke would be spread out extremely dilute, and specific nuclear weapon designs which minimize neutron activation can keep the radioactivity very low. A more serious concern is that you don't know the trajectories of the resulting fragments, some of which might still be dangerous, and thus it would be a very bad idea to destroy it before impact was a certainty, but then waiting until the last minute to stop it is a major risk in itself. More safe would be to detonate the nuclear device near the asteroid. This would vaporize a thin layer of the surface of the asteroid in line of sight of the explosion, sending it flying off into space at extremely high velocity and propelling the asteroid equally in the opposite direction. There are two major advantages to this approach: it will work against targets regardless of their composition and internal structure (very beneficial if we don't have time to study the asteroid ahead of time) and the method can be done repeatedly to the same target - we could launch dozens of independent interceptors and just keep detonating them one by one until we get the desired result. While the goal is to have the asteroid not impact at all, and thus radioactivity is even less of a concern, this option does produce even less radioactivity than blowing up the asteroid. From a strictly technical perspective this option is pretty much a no brainer, but obviously building a battery of dozens of nuclear missiles is politically problematic.

shagie 4y ago
A sibling comment of mine references https://www.adrc.iastate.edu/files/2012/09/IAC-09.C1.3.1.pdf https://www.adrc.iastate.edu/files/2012/09/IAC-09.C1.3.1.pdf Section 6.1 is on nuclear stand off explosions. > The nuclear standoff explosions require an optimal standoff distance for a maximum velocity change of a target as- teroid. Therefore, we have to determine how close the nuclear explosion must be to effectively change the or- bital trajectories of asteroids of different types, sizes, and shapes. The precise outcome of a NEO deflection at- tempt using a nuclear standoff explosion is dependent on myriad variables. Shape and composition of the tar- get NEO are critical factors. Section 6.2 is on kinetic impacters... > A somewhat futuristic, solar sailing mission concept utilizing a 160-m solar sail to deliver a 150-kg kinetic impactor into a heliocentric retrograde orbit was studied in [25-28]. Such kinetic impactors will result in a head- on collision with a target asteroid at its perihelion (as illustrated in Fig. 1), thus increasing its impact velocity to at least 70 km/s. The NEAR Shoemaker study of as- teroid Mathilde and the Japanese Hayabusa mission for exploring the asteroid Itokawa suggest that many aster- oids are essentially “rubble piles.” Consequently, a practical concern of any impulsive approaches employing kinetic impactors or nuclear explosions is the risk that such high-energy deflection attempts could result in the frag- mentation of NEOs, which could substantially increase the damage upon Earth impact. And then, section 6.3 is a fun one: Gravitational Binding Energy > the disruption energy per unit asteroid mass is predicted to be 150 J/kg for strength-dominated asteroids. This indicates that a strength-dominated, 200-m asteroid would not be disrupted by a 150-kg impactor at a high impact velocity of 70 km/s. Also in Ref. 5 (pp. 135-136), the energy (per unit asteroid mass) required for both disruption and dispersion of a 1-km asteroid is predicted to be 5 kJ/kg. Thus, the feasibility of the most kinetic-impact approaches for either disrupting or deflecting an incoming NEO depends on its size and composition (e.g., solid body, porous rubble pile, etc.), as well as the time available to change its orbit. These are from 2012, and we've had a decade more experience (and a mission to try it out) since then... but it's interesting to look at and the math in the paper doesn't change.
LargoLasskhyfv 4y ago
Lots of small rocks can cause a 'heat pulse' over wide areas on atmospheric entry.

pif 4y ago

In order to change its trajectory, you need some wisely applied momentum, not a catastrophic explosion. The most powerful explosion may at most reduce the size of the biggest chunks, but not change the vector velocity of the barycentre at all.

0cf8612b2e1e 4y ago
My completely naive take: if something is X AU away from the planet, why wouldn’t the tiniest course change result in missing the Earth by a huge margin? Even a fractional alteration of momentum in any off axis direction seems like it would have the desired effect. It feels like smashing any available rocket into the side of a non accelerating body would be effective, but space physics is weird, so I must be missing something.
- pif 4y ago
  Your analysis is correct and wrong at the same time. You are not considering the fact that we currently are not able to observe a rock a few AC away with the precision that is necessary to assess that it is going to hit us, and that the gentle punch we can give it will not worsen the situation.

more_corn 4y ago

Blowing it up doesn’t work. Turns a cannonball into buck shot. Seeing it early is the ticket. A tiny thrust over a long period of time is the way to move things in space.

helloworld11 4y ago

>What truth is there to this? Suppose this asteroid was on a collision course with earth, would we have any recourse other than praying it lands in Siberia and not NYC. If your asteroid is only 20 to maybe 400 meters across, having it land somewhere absurdly remote on land or far off into the deep oceans would minimize harm, but for asteroids much bigger than that (and even 400 meters is really stretching the bounds of acceptable size), it doesn't really matter where the impact happens, millions or more people will almost certainly die. If you scale up to a size of, say, 900 meters or larger, then you're talking global multi-year catastrophe no matter where the impact is. If you then scale up to over a mile or two in diameter, then you're talking global multi-decade cataclysm no matter where the impact site is. So yeah, even with Siberia, the Canadian North, Antarctica, the Sahara or the central pacific ocean. Any size beyond a few hundred meters makes specifics not so important in terms of death toll and major climate effects.

__s 4y ago

NASA's recent DART project was testing this question The sooner the threat is detected the lighter the necessary response

Rebelgecko 4y ago

NASA's Dart mission yeeted itself into Dimorphos a few weeks ago to gather data that will hopefully help build a model of how much energy it takes to divert an asteroid.

yodon 4y ago

> praying it lands in Siberia and not NYC The Siberian Tunguska event was thought to be caused by a 20m diameter object hitting the earth. This is talking about a 900m diameter object which likely has 100,000x the mass of the object that hit Tunguska. EDIT (per comments below): 400,000x the Chelyabinsk object 27,000x the Tunguska object

lloeki 4y ago
> 900m diameter Article says it's 0.9mi, so 1.5km > 20m That was Chelyabinsk, Tunguska is thought to have been 50-60m
- yodon 4y ago
  Interesting: Google's search snippet for 'how big was the tunguska meteor' found and reported a 20m size estimate from the Tunguska wikipedia page, but on manually reading the wikipedia page it becomes apparent that size estimate is for the Chelyabinsk meteor (which is also discussed on the the Tunguska wikipedia page).

Normille 4y ago

>...praying it lands in Siberia and not NYC. or vice versa.