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Suddenly, the news warn of a civilization-resetting asteroid/comet about to hit the earth in hours. No-one knew a thing.

Why? Well, my research shows that such an event is extremely unlikely in any case. That's fine. But if it did happen, why?

If my limited research is correct, there are two possibilities:

  1. An asteroid, amongst the small percentage of undetected asteroids in our solar system, starts plummeting towards earth, hidden by the sun's glare.

  2. An asteroid/comet with a very low albedo starts heading for earth.

I don't know if the above is correct and if so, comprehensive. I don't see how the sun's glare can have much to say; surely it would only stay in the sun's glare for such a small amount of time so as to not have a very big impact on detection time.

So, what may the reasons be that our contemporary world doesn't detect an incoming object of the size required to, say, make the dinosaurs go extinct?

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    – L.Dutch ♦
    Commented May 9 at 16:17

13 Answers 13

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The near-Earth objects we look for are mostly in the plane of the ecliptic, because that is where the vast majority of solar system material not in the Sun is to be found.

The object that is about to hit Earth is coming from an extremely high angle of inclination, either because it is an Oort cloud comet that got sent to the inner solar system or an interstellar object or nefarious aliens wanted to make sure the job got done right.

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    $\begingroup$ If you're going to postulate nefarious aliens you might as well have them paint the asteroids black to help reduce the chance of premature detection (cf. The Expanse.) $\endgroup$
    – Michael Seifert
    Commented May 6 at 18:25
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    $\begingroup$ Nefarious aliens know enough about humans to know we don't have a chance in hell of doing anything about it. I suspect they would sooner paint it reflective silver so we have the greatest chance possible of spotting our incoming doom. $\endgroup$
    – SoronelHaetir
    Commented May 6 at 19:29
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    $\begingroup$ @soronelhateir Why take the risk that we might find a way to deflect asteroids during the time it takes to get to earth? It takes a long time to send something from the Oort cloud to earth. $\endgroup$
    – Bubbles
    Commented May 7 at 13:47
  • $\begingroup$ I read about this possibility too; crazy that that's all it takes. $\endgroup$
    – user110391
    Commented May 7 at 21:11
  • $\begingroup$ @MichaelSeifert: Wouldn't the earliest warning come from infrared and radio telescopes, not visible-light ones, tho? $\endgroup$
    – Vikki
    Commented May 8 at 3:52
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So a counterpoint to your view.

The world thinks there is no warning system, not because it doesn't exist, but because the world has no way to respond to this information. A world ending meteorite would travel at a speed and be of a size that not even any of our nuclear weapons could deter it!

Why doom the common folks with the knowledge they only have a week to live? Would the riots that ensue really better if we gave them weeks of notice vs just a few hours? The few hours warning would likely be since at that point they can't hide it anymore.

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  • $\begingroup$ I completely agree that this solution is viable if your scenario is merely "humanity is hit by a large asteroid/comet". But my scenario also includes the criterium that humanity only finds out about the object a few hours before, not just to help explain why they didn't prevent it, but also because that fits better into the plot and narrative. $\endgroup$
    – user110391
    Commented May 7 at 21:15
  • $\begingroup$ Does your plot require that no humans at all knew about it beforehand, or just that the vast majority did not, because those who did know chose not to tell them? (Let's not worry the people about things we can't do anything about anyway.) If it's just that you don't want those in the know to have a chance to escape to a safe bunker, just make your asteroid such that no bunker is safe. $\endgroup$
    – Miral
    Commented May 9 at 5:50
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    $\begingroup$ Honestly that could be an interesting twist in the plot development. The NEAR survey folks knew about the object with maybe a few days warning, but realized given the speed and size there was no hope of defending against it. So maybe only defense apparatus and world leaders know. It's only when it gets close enough that amateur astronomers are able to see it that word gets out. $\endgroup$
    – DeusXMachina
    Commented May 9 at 14:03
  • $\begingroup$ "If it's just that you don't want those in the know to have a chance to escape to a safe bunker, just make your asteroid such that no bunker is safe." Yeah, but the story might get a bit boring with no characters... $\endgroup$
    – user110391
    Commented May 20 at 13:15
  • $\begingroup$ "Honestly that could be an interesting twist in the plot development. The NEAR survey folks knew about the object with maybe a few days warning, but realized given the speed and size there was no hope of defending against it." I have contemplated this, but I feel iffy about it, given that I have no idea how likely it is that they would successfully keep it secret until the amateur astronomers catch up (and even choose to do so in the first place). $\endgroup$
    – user110391
    Commented May 20 at 13:16
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The Asteroid was caused by the collision of 2 other asteroids that were not anticipated to hit earth

So, there are two asteroids flying on a merry orbit, close-ish (in astronomical terms) to earth - they are not anticipated to hit - everything is good. However, if one of the asteroids is significantly denser than the other, then some unknown gravity shenanigans can happen - the asteroids collide with each other and this collision causes a big chunk to break off and head towards earth

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  • $\begingroup$ How is one being denser makes its orbital path unpredictable? There is no such thing as unknown gravity shenanigan. $\endgroup$
    – stackoverblown
    Commented May 7 at 13:17
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    $\begingroup$ @stackoverblown In a two-body system, we can pretty much perfectly model everything. 3-body system however is extremely difficult, and the more bodies there is, it gets exponentially more difficult to model all the bodies for any significant length of time. These asteroids probably have thousands of bodies influencing their orbit, so it is extremely difficult to predict their orbit without just waiting to see where it goes. If something new happens this orbit, we may not be able to predict it. $\endgroup$
    – Bubbles
    Commented May 7 at 13:49
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    $\begingroup$ @Stackoverblown no, just an unhealthy interest in orbits. We can't simulate complex systems like the asteroid belt very well, so there are bound to be unexpected changes that we can't predict. $\endgroup$
    – Bubbles
    Commented May 7 at 14:30
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    $\begingroup$ @stackoverblown no, it is not. However, they can still be flung toward earth, either due to unexpected collisions(as mentioned here) or just weird interactions, and the earth can drag them in the rest of the way. My point is that it is pretty unpredictable at this level. $\endgroup$
    – Bubbles
    Commented May 7 at 15:16
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    $\begingroup$ +1. It doesn't have to be a collision as well - perhaps the asteroid broke up for whatever reason. $\endgroup$
    – Allure
    Commented May 9 at 2:20
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It could be an extra-solar object like 'Oumuamua. That would explain why it hadn't previously been detected. A sky survey might pick it up, but since it's heading almost directly towards us on a hyperbolic trajectory it would just be another small dot moving slowly across the sky and might not appear to be of much concern. But once it gets closer its brightness starts rapidly increasing and people start wondering what it is. By the time someone finds the sky survey data, calculates the trajectory, and realises what's about to happen, there isn't going to be much time before it does. This will probably be a civilisation-ending event due to the high velocity of the impactor.

If this did happen, I think it's quite plausible that we would have very little warning - the only problem is that an interstellar object on a collision course with Earth is fantastically unlikely - much, much more so than a regular meteorite strike.

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    $\begingroup$ ... which would make for a quite intriguing premise, if part of the plot is figuring out what or who made this astronomically improbable event happen. $\endgroup$
    – ojdo
    Commented May 6 at 16:48
  • $\begingroup$ If it was a very dark object traveling at very high velocity it would make detection even harder $\endgroup$
    – Slarty
    Commented May 6 at 17:27
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    $\begingroup$ Objects that are not in orbit around the sun, like Oumuamua also travel way faster than the velocity of a solar bound asteroids or comet. ~50+ miles per second vs, roughly 25 miles per second for a average comet. $\endgroup$
    – Gillgamesh
    Commented May 6 at 17:28
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    $\begingroup$ @Gillgamesh and don't forget that twice the velocity is four times the kinetic energy - it's going to be a powerful impact. $\endgroup$
    – N. Virgo
    Commented May 7 at 12:19
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Really bad luck

Estimates show that an asteroid in excess of 1 kilometer in diameter impacting Earth would be a civilization-kill event. While we have found over 90% of near earth 1-kilometer asteroids, 90% isn't 100%(As stated here https://cneos.jpl.nasa.gov/stats/#:~:text=With%20over%2090%25%20of%20the,population%20larger%20than%20140%20meters.). There is a chance that a low albedo asteroid, obscured by the sun's glare, went unnoticed, and is on an impact course with Earth, or that a cataloged asteroid changed course due to weird interactions with other bodies, and is now h headed towards earth. And if it isn't a near-earth asteroid, then this is even more likely, and there is plenty of asteroids around.

Extra justification for why it wasn't found when it was near Earth is because most scopes were trained on another flyby, causing them to miss this one, much like what happened in the Chelyabinsk asteroid, where it went unnoticed due to many telescopes being pointed at another asteroid doing a close flyby. Say, there is a really interesting comet doing a close flyby of Earth, meaning that few telescopes are looking for nearby asteroids. This might lead to it going completely unnoticed until the last second. While it is a bit unlikely, so is an asteroid impact in general, so that's the best I can come up with.

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  • $\begingroup$ Oooh, I like that! "Wow, that was clo..... ohshit." $\endgroup$
    – William
    Commented May 6 at 19:50
  • $\begingroup$ Short-time distractions won't work. Trajectory calculations just need two or three observations for maybe a few seconds or minutes each, with days, weeks or months between observations. Spectacular events may cause some observatories to reschedule some observation slots, but the impact on normal observation programs is low. $\endgroup$
    – toolforger
    Commented May 8 at 8:27
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    $\begingroup$ @toolforger Those trajectory calculations aren't perfect. Unexpected interactions with other bodies can fling asteroids out of their orbits, and there isn't a scope on them constantly. It could be months before someone takes a look and realizes the asteroid isn't there anymore. Especially if there is a much juicier target like a comet doing a flyby to take a peek at. $\endgroup$
    – Bubbles
    Commented May 8 at 16:25
  • $\begingroup$ Sure. That's why trajectories are routinely rechecked. Multiple months until clash is plenty of time for that, in particular since you still need a minute or whatever to check whether that dot is still where it was expected. $\endgroup$
    – toolforger
    Commented May 9 at 14:09
  • $\begingroup$ @toolforger I think you are underestimating the amount of asteroids there are. We do not have enough telescopes to constantly check in on them. They can go for fairly long periods between observations. $\endgroup$
    – Bubbles
    Commented May 9 at 14:44
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Maybe it doesn't orbit; it's an interstellar object that strikes the Earth on the way through. We had our first recorded passage through the solar system of an interstellar object recently: https://en.wikipedia.org/wiki/%CA%BBOumuamua .

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This might seem simple, but it does explain the "Why did we not notice this ?"

The asteroid is moving significantly faster than usual. (Maybe it's naturally accelerated, maybe it isn't, depends on if it even is relevant to your story)

So fast in fact that from the maximum range we can detect it, to earth, it only takes a couple of hours. That's why we didn't notice it or knew anything, we couldn't have.

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  • $\begingroup$ That asteroid would be faster than the solar system's escape velocity. Interstellar rocks are really fast, but they still take months from entering the solar system to leaving it. $\endgroup$
    – toolforger
    Commented May 8 at 8:29
  • $\begingroup$ @toolforger I am taking this idea from some book I read where they used asteroids to attack and kind of slingshot them to near light speed. I don't fully understand what an interstellar rock entails, but the user didn't ask for questions to be answered with proof, so I guess it's OK for it to be a (a lot) unrealistic. $\endgroup$
    – Or4ng3h4t
    Commented May 8 at 10:06
  • $\begingroup$ Near light speed means you get significant drag from interstellar medium. That's why interstellar rocks have a bit of a speed cap. Now you could speed up rocks, but if you want near-light speed, high-energy particles are much, much easier to accelerate and just as effective. See youtube.com/watch?v=tybKnGZRwcU - the star laser will fail unless they can phase-control the lasers, but there are no obvious problems with the other two. $\endgroup$
    – toolforger
    Commented May 9 at 14:23
  • $\begingroup$ @toolforger That's so cool, thanks for the explanation, I honestly thought that there was no such thing as drag in outer space due to lack of an atmosphere, I guess I have to look into it $\endgroup$
    – Or4ng3h4t
    Commented May 9 at 15:07
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    $\begingroup$ You're welcome :-) -- Interstellar drag is insignificant most of the time, and most explanations ignore the insignificant factors. However, as soon as you change any parameter by more than, say, an order of magnitude, some of the insignificant factors will become significant. That's why, e.g. the magnetic field of the galaxy, usually completely irrelevant, becomes relevant when you model billions of years of development. Near-light speed is so many orders of magnitude beyond the usual that you can expect all sorts of change. $\endgroup$
    – toolforger
    Commented May 9 at 15:11
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We Were Getting Our Rocks Off

In a near future where humanity is experimenting with moving meteor fragments or high albedo debris around via drone "tugboats", we may end up cluttering up the sky with our activity. Perhaps an ISS module or a space mission had some kind of severe module failure, leaving highly reflective space trash for us to clean up.

Add to that the existing problem of how much space there is to watch, and we could blind ourselves to an incoming Chixculub 2.0 until it was too late

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The object had a near-miss with the moon, and was pulled on to either a very different trajectory, or had been predicted to hit the moon, and didn't, again ending up on an Earth-intercepting trajectory.

Due to the proximity of the moon, we would have very little time to react.

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    $\begingroup$ I think that we would know well before hand that ti would interact with the moon, although not necessarily sure that it will hit, there will be advanced warning of the risk. $\endgroup$
    – Bubbles
    Commented May 7 at 14:37
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Simple: You're looking for a needle in a haystack.

How much stuff is in the sky in your solar system? Few objects? Easy to track and spot... Many? harder to spot.

Many upon many? harder and harder to spot.

The sky is full of stuff that's moving and it's hard to know what's going where and when it'll hit. It's a young system with lots of moving stuff.

Edit: My idea could also work in an older universe where there's a lot of space debris. Basically, how can you tell if something big is coming your direction if there's a lot of clutter and objects to track? Even high tech could have issues tracking a massive cloud of asteroids, comets, space trash, etc.

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There is a lot of research on this just now. Almost all money spent on space is wasted. We are not going to New Worlds, and bring back gold, tobacco, and slaves. However, spotting an earth-hitting asteroid and deflecting it could give a return on our investment: maybe biggest return of all in saving the Earth and everything on it. So there is a lot of research on this just now. If this object appeared today, then we are probably boned, but we are working on the answers.

We still do not know what is out there. Most of the incoming stuff belongs to the solar system and Oort Cloud, so it is mostly about the ecliptic. Interstellar objects such as Oumuamua are much rarer. A lot of the spotting is confined to the ecliptic.

Oumuamua was a long, thin object with a low albedo. We saw that. We don't have enough big telescopes looking in all directions yet, but we could. Unless this is an attack on Earth, the odds of something travelling interstellar distances, then hitting the earth are huge.

It is hard to spot objects close to the solar disc. However, if we are making a spotter network, the logical thing is to put telescopes out at Lagrange points L4 and L5. The greater parallax gives greater precision on the trajectory predictions. The other advantage is that if the object is coming at us 'out of the sun', it would be sixty degrees away for the next telescope.

Extrapolating from your question a bit: suppose we had the defences against meteorites we are currently proposing, what naturally occurring and not wildly improbable object might take it by surprise?

A sun-grazing trajectory would be hard to predict. The object may be coming in fast towards the sun, then get deflected through a significant angle. If it has volatiles, it may outgas violently, changing its orbit when it is close to the sun. It may be around the back of the sun when this happens. We get to see the modified trajectory too late to do anything about it.

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  • $\begingroup$ A near earth asteroid/comet with a surprise outgass would be the only realistic way to surprise NASA. But I think it would need to be fairly close to Earth when it happened. Like one of those missed us by 20,000 mile events that suddenly isn't going to miss. $\endgroup$
    – lucasbachmann
    Commented May 7 at 17:39
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Starlink.

Actually, more generally, the clouds of satellites we are putting in orbit these days. They're a royal pain for the astronomers and will make it harder to detect rocks. A bit of bad luck blocking routine observations could mean a threat actually was seen but not noted as such--just because you see it doesn't tell you anything about the threat it poses. I believe the minimum is three observations to derive an orbit and precision is a function of both how accurate and how far apart they are.

Your rock gets a streak across it a couple of times, the next time it's picked up it is at first thought to be a different rock. Eventually enough observations are made that someone thinks it might be coming close--then the big boys look, they get a parallax. Then the world collectively fills it's underwear.

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Assuming this is in the current Earth scenario, there are a few possibilities I can see and it depends on how much time you wanna give to the population:

Decades: it is a very bad luck scenario of a direct hit from a body out of the solar system.

%: It is not going to hit Earth, but the moon. A body hit the Moon an it was not very big or very fast, but its composition was unknown and something happened on impact: It exploded. With enough thrust to send many debris to Earth.

(Very imaginative scenario now, not to say ridiculous) Years: Activity in a Saturn's moon (probably Enceladus) made it eject gases with enough thrust to change the moon's orbit. The change was enough to cause a chain reaction in its rings and some impacts later a giant ice body left the outer rings. It's coming in our direction. It is coming fast. It will destroy all the platypuses and the rest of Earth too.

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