What requirements would a meteor have to satisfy, to approach Earth unrecognized until hitting the atmosphere and cause climatic changes after the impact?

  • The meteor should have at least a circumference of 500 meters at impact to cause something.
  • It might have to hit earth at land because at sea there would be tsunamis and mostly no climatic change.
  • The climatic changes should be an impact winter but if there are other ideas they are very welcome!
  • If camouflaging the meteor is naturally possible then i would prefer this way. If not we are at the actual technology level.


  • The Meteor should remain undiscovered until the discoverer has no time left to make his discovery public before the impact.
  • $\begingroup$ At what tech level? Modern day? $\endgroup$
    – Erik
    Mar 9, 2016 at 13:17
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    $\begingroup$ Vantablack is all the rage with the kids on the internet at the moment. $\endgroup$
    – Separatrix
    Mar 9, 2016 at 13:48
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    $\begingroup$ I see a meteor and I want it painted black ... No colors anymore I want them to turn black ... $\endgroup$
    – brhans
    Mar 9, 2016 at 20:13
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    $\begingroup$ Do you actually need it to be undetected until it hits the atmosphere, or do you simply need to make sure we can't do anything about it? $\endgroup$
    – Cort Ammon
    Mar 10, 2016 at 5:15
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    $\begingroup$ No additional requirements, they are already very difficult to detect. There could be large inter-stellar body approaching earth now at .75c or so and we'd be extremely "lucky" to spot it before it caused a cataclysmic event on earth. The real challenge would be getting it to hit the target. $\endgroup$
    – Jodrell
    Mar 10, 2016 at 11:52

7 Answers 7


Cover it with carbon black then approach from the sun-ward side

This is something of the current nightmare scenario for real life planetary scientists. An object covered in carbon black between the star and an observer is incredibly hard to see against the black background of space since the IR radiation from the star is radiated back towards the star instead of towards the observer.

Carbon black has an incredibly broad absorption spectrum that covers the entire visible spectrum and into the IR range. Because of this broad absorption, there is very little visible light for a conventional telescope to detect. In addition, trying to pick out a very dark object in the glare of a star is very difficult.

  • 2
    $\begingroup$ " is radiated back towards the star " - why would that be the case, exactly? Also, absorption does not prevent black-body radiation. If it absorbs, it's hot, or at least warm. If it's hot, it radiates in all directions. $\endgroup$
    – Mołot
    Mar 10, 2016 at 0:36
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    $\begingroup$ @Mołot The side that gets hot from sunlight is the side facing the sun. Make sure it's not rotating so that hot side doesn't rotate around to face Earth. A rock that big won't heat through in the time involved. $\endgroup$ Mar 10, 2016 at 3:26
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    $\begingroup$ If you make its backside reflective, it will heat even slower. $\endgroup$
    – corsiKa
    Mar 10, 2016 at 7:41
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    $\begingroup$ @nwp, what you're suggesting is equivalent to trying to pick out individual grains of sand thrown in front of a large flood light at night. It's tremendously difficult to see anything but the floodlight. It can be done, sure, just really hard. $\endgroup$
    – Green
    Mar 10, 2016 at 13:46
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    $\begingroup$ Technically using that in World Building would be illegal, since that color is copyrighted, apparently. $\endgroup$ Mar 11, 2016 at 2:12

Paint it black.

Have it moving really fast, and have it come in from above or bellow the plane of the solar system.

If it was painted black(with a nice thick layer of some some kind of tarlike substance) they probably wouldn't see it coming at all. We just don't watch space that carefully with very many telescopes. If we didn't know where to look we'd have no chance and if we did know where to look we might still miss it.

It's really hard to spot even much larger objects on slow lazy swings around the sun.

Additional details for this kind of scenario: How far away could Earth detect a projectile travelling at relativistic speeds?

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    $\begingroup$ +1.5 for a primitive solution that actually works; -0.5 for a solution that might not work, given enough luck to astronomers. $\endgroup$ Mar 9, 2016 at 14:07
  • $\begingroup$ This substance may be of some use: techinsider.io/vantablack-blackest-darkest-material-2016-3 $\endgroup$ Mar 10, 2016 at 15:09
  • $\begingroup$ I like this one because it's probably how it will happen. $\endgroup$
    – jorfus
    Mar 16, 2016 at 23:04

The Science Fiction Method

Get the whole thing painted with this type of paint.

.#start rant
It would be practically impossible, but who gives two dimes to practicality when you are into making comets invisible from detection?
.#end rant

Also it should be a small to medium sized comet. You cannot expect a huge Baptistina sized body to not be identified due to its gravitational effects on nearby objects when travelling in the inter-planetary space.

The Other (Practical) Method

You would need to hack into the computer systems of NASA and European Space Agency and shush out any and all information they transmit about the comet. The comet might still be visible from naked eye by the folks up there in ISS, but it would only be a few minutes between seeing it and it crashing down into Earth's atmosphere.

  • $\begingroup$ +1 for the NASA hack, though the OP wanted a non-technological solution and this would also be just an illusion. $\endgroup$
    – Nick
    Mar 9, 2016 at 19:02
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    $\begingroup$ Making a whole huge comet/meteorite invisible is pretty much non-realistic thing considering our current tech levels ^_^ Hiring some Russian and Chinese hackers to hack into nasa and place a bug in their software is by far the more practical approach than launching a rocket from the surface, reaching a huge space object that is travelling towards you at high speeds, landing on it, and then painting it with whatever ghastly thing you brought with you in that spaceship :p :D $\endgroup$ Mar 9, 2016 at 19:27
  • $\begingroup$ My interpretation is that it should be hidden from everybody. The Russians or Chinese may be able to hide it from NASA, but I would think they would have a vested interest doing something once they are aware. $\endgroup$
    – GRW
    Mar 9, 2016 at 19:34
  • $\begingroup$ Oh yes. I forgot to include European Space Agency too. Now you would have the Russian/Chinese space telescopes detecting a giant comet heading towards Earth while the Europeans and Americans would detect nothing. A whole process of error detection in all observatories would initiate immediately (who knows maybe the error was in Chinese and Russian computers who are showing erratic results?). By the time they find out what was wrong ... well ... comets and asteroids travel very fast ... $\endgroup$ Mar 9, 2016 at 19:44

Hide it in full view — Just make it Fast EnoughTM

Make it small and fast. The important thing is the impact energy; a very fast and small enough thing, painted yellow and red with the sign "LOOK AT ME, I'M COMING" is practically as good as invisible.

Mandatory reference to Randall Munroe's What If site.

(By the way --- in that case I really suspect that hitting sea or land will make little difference. Couple of kilometers of water instead of air will be just a microsecond nuisance).

  • $\begingroup$ This is correct answer. If the meteor is fast enough, nothing else matters, as XKCD explains. $\endgroup$ Mar 10, 2016 at 17:23

Have it approach from lots of different directions.

If your plan is to intentionally harm your target planet (and you have unlimited resources and very good orbital mechanics at your disposal) then you could have your meteor approach in 100,000 magnetically charged pieces, converging on a single point somewhere just inside the Earth's orbit.

Individually they'd just be too small to see from any reasonable distance but collectively, once they hit each other they would stick together to form a gigantic meteor that seemed to instantly appear from nowhere before dropping onto Paris.

As an added bonus, you could paint it whatever colour you please. It really wouldn't make that much different since the pieces are tiny.

  • $\begingroup$ What is going to happen to all the kinetic energy when they combine? How do they stick together rather than flying apart again? $\endgroup$
    – Tim B
    Mar 10, 2016 at 15:43
  • $\begingroup$ @TimB - Hence magnets $\endgroup$
    – Richard
    Mar 10, 2016 at 15:47
  • $\begingroup$ @TimB - As an added bonus, if you arrange for them to turn up in Earth's orbital path, the pieces don't need to be moving at any great speed. Any annoying kinetic energy can be turned into rotational energy if you want. $\endgroup$
    – Richard
    Mar 10, 2016 at 15:51
  • $\begingroup$ Magnets both repel and attract each other. Additionally you'd need a ridiculous strength magnetic field to deal with the sort of energies we're talking here. I really like it as a concept but it doesn't quite work how you've suggested it so far. $\endgroup$
    – Tim B
    Mar 10, 2016 at 15:51
  • $\begingroup$ Perhaps bring in all the pieces on parabolic orbits so they don't need to hit each other at all but all enter the atmosphere at roughly the same location and velocity. $\endgroup$
    – Tim B
    Mar 10, 2016 at 15:53

I was thinking about suggesting maybe a fragment of neutron star since that would allow you to get the same mass in a much smaller area.

Unfortunately it seems the smallest size a neutron star could be and remain a neutron star is 0.1 stellar masses. That's 33 thousand times the mass of the earth so doesn't really work. (see https://physics.stackexchange.com/questions/143166/what-is-the-theoretical-lower-mass-limit-for-a-gravitationally-stable-neutron-st)

Average meteorites though have a density of 3g/cm. Make the meteorite out of something like gold or uranium and you can get the density up to 20g/cm. You should also make the meteorite spherical to get as much mass as possible for the cross section. Unfortunately square-cubed is not working for us here as a factor of 3 increase in density does not give us a factor of 3 decrease in cross section.

However it doesn't need to be a sphere. If you can control the meteorite's orientation and rotation finely enough you could shape it like a very long rod with one end pointed towards the earth. Make that end black and inclined at an angle so it doesn't reflect anything back towards earth.

You can now make the meteorite as massive as you like by extending the length of the rod without making it any more visible at all.

An important point to make though is that there is no need to camouflage it at all. We do not watch all the sky all the time, and not even all the meteors that we know are out there have been found yet. You don't need to explain a meteor not being spotted unless you want that explanation to be significant. It's actually more likely we would not spot one than that we would.

  • $\begingroup$ The idea is amusing but the ridiculously complex rotation it would have to maintain wobbling through space in order to maintain that alignment with respect to earth is kinda silly, don't you think? $\endgroup$
    – The Nate
    Mar 14, 2016 at 0:27

500 meters isn't very big. They are hard to spot at the best of times.

The bulk of meteors are in the plane of the ecliptic. A long period asteroid at a high angle to the ecliptic may not have been spotted yet. If it comes to Earth after closest approach to the sun, then it would have been in the glare of the sun for it's final approach, and far enough away to be hard to find before.

It takes several locations to pin down the orbital parameters of an asteroid. MANY asteroids have been found, lost, found again.

Remember too that Jupiter keeps re-arranging orbits. It's quite possible that an asteroid whose aphelion is out close to jupiter could lose enough energy that the other end of it's orbit becomes a colider. Some of this will depend on the funding that the skywatchers get. There is a lot of sky out there. It doesn't all get photographed every Tuesday.


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