Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Doomsday Asteroid

  1. Mar 19, 2005 #1
    Just curious, you know the movie armageddon? well, i was thinking, how big would an asteroid really have to be in order to wipe out all the life on earth? and, what're the calculations you'd do to figure that out? Thanks...

  2. jcsd
  3. Mar 19, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Really big. No asteroid has yet succeeded at that task and I suspect that there isn't one big enough to do the job. That would likely require something to happen to the sun (or for us to run into another planet). As for the size of asteroid required to kill all humans, I could give a very rough estimate of 3-5 km, but that's mostly a guess. The one that killed the dinosaurs is thought to be of order 10 km and I'm pretty sure that would kill us off.

    There's no simple calculation that will give you a definite answer, but perhaps the most important quantity is the total energy deposited:


    where m and v are the mass and final velocity of the asteroid in question. This indicates that the asteroid's velocity is important, meaning we'd be worse off hitting one head on than taking it in the rear. A lot of other factors would have to be considered, however. For example:

    - Where it hit. Ocean and land collisions would have a different effect, kicking up different kinds of materials into the atmosphere or inducing tsunamis.
    - What it was made of. An asteroid that's more tightly bound would likely do more damage. Also, composition will determine whether it fragments in the atmosphere and what impact this will have.
    - What its shape was. The reasons here are similar to the ones for composition.
    - How fast it was rotating. This will change the character of the collision, as well as the amount of energy deposited.
  4. Mar 19, 2005 #3


    User Avatar
    Gold Member

    Arent there a LOT of asteroids out there that size or greater? You may be giving off the impression that asteroids of that size are very rare in the universe... unless im mistaken
  5. Mar 19, 2005 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    There are quite a few, yes. Why do you think I'm giving that impression?
  6. Mar 19, 2005 #5


    User Avatar
    Staff Emeritus
    Science Advisor

    You might be interested in the University of Arizona's "Impact Calculator" program on the WWw - it's at


    A 25 km radius impactor won't "wipe out all life on earth", but it will (with the inputs I entered)

    ignite all trees, grass, and most other flammable objects in the region from which the fireball is visible (about 2000 km according to the program).

    Flatten all trees within 6000 km (the hemisphere of the impact), destroy all buildings within 3000km of the impact, shatter glass windows on the opposite side of the planet (12,000 km).

    Put a LOT of dust and ejecta into the atmosphere (the climate effects are not modelled)

    Impactors of this size arive avery few billion years on the average - the Earth has probably encountered one in its history.
  7. Mar 19, 2005 #6


    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    These days, most orbital bodies have found stable orbits. The risk is fairly small. Even Jupiter, the most likely candidate for a collision, rarely suffers them.
  8. Mar 19, 2005 #7
    thanks pervect, thats a really neat little calculator. Thanks everyone for the replies, actually. Curious still, what sort of conidtions would be necessary to wipe out even bacteria? And, would an impact that size significantly effect the earth in other ways too? like warp the orbit or spin? thanks again...

  9. Mar 19, 2005 #8


    User Avatar
    Gold Member

    When you said "Really big.", to me it felt like you meant extraordinarily big because on a astronomical level... 5km wide doesnt seem like much at all.
  10. Mar 19, 2005 #9


    User Avatar
    Gold Member

    The atmosphere would be enormously affected. The spin might change... the orbit woudl change but not really sure by how much. Lets hope we never have to find out :D
  11. Mar 19, 2005 #10


    User Avatar
    Science Advisor
    Gold Member

    There are a few asteroids in the hundreds of kilometers range, (Ceres, Vesta, Pallas). None are in danger of hitting Earth in the forseeable future as their orbits are beyond the orbit of Mars.

    To wipe out even bacteria, an impact would have to melt the Earth's crust, creating a magma ocean. But even if Ceres had enough energy to do that, and it struck, bacteria life could still survive in the following way: The collision would shoot rocks into solar orbits. Like the Martian meteor found in Antarctica, bacteria could survive for millions of years on these rocks. Many of these rocks would ultimately collide with the Earth again, delivering their bacteria back home.

    Just my guesses.
  12. Mar 20, 2005 #11


    User Avatar
    Science Advisor

  13. Mar 20, 2005 #12
    Massive asteroid passing relatively close to the earth (not necessarily colliding with it) can cause huge cataclismic disturbance here on the earth.
  14. Mar 20, 2005 #13
    true, but it had better be a lot bigger than the moon (not many of them) and come a lot closer (not very probable)

    The number of stars that were larger (compared to sun) aged rapidly (compared to sun) died and now are gravitationally bound black holes is probably greater than all the stars that currently are emitting light! i.e. more than all the grains of sand on all the Earths beaches!

    Iron meteors are probably produced during the irregular implosion of a supernova when the iron core can no longer make heat but the layers out side still can. That is the implosion is very asymeteric and pieces of the core escape. Probably there are big pieces somewhat separated also. If the first generation stars were roughly 100 solar masses (universe mush smaller and denser back then) it seem at least possible that some to 10 to 20 solar mass once iron chuncks could be separate, gravitationally-bound Black Hole pairs now. this also supports the idea that there may be a lot of them unseen, but existing. One of them could pass a million times the moon's distance from Earth and yet do us in, via producing an orbit more excentric which results in an new extreme ice age, etc.
    Last edited: Mar 20, 2005
  15. Mar 24, 2005 #14
    :smile: I'd like to digress a bit on this topic. You know it wouldn't be very difficult to launch small "Engins" that could meet up with an asteriod, of any size you wish, then grappel onto it and thru the magic of vector steering bring it into a stable orbit for mining. Some of those things must contain large amounts of various minerals. Now, :devil: about the doom and gloom :devil: aspect. I see no reason why we could not capture one of these things and hurl it at any military target on the planet; without even being on the side of earth you want it to strike. One might simply choose an asteriod of the necessary size to produce the damage required over a given terrain. And afterwards, and heres the beautiful part, militarily I mean; there wouldn't be any nasty radiation to contend with. :cool: Just strike and move in after the dust clears. This would be a weapon that could be easily held ready for use with a minimum of cost, deployed on a moments notice. Why wait for nature when we can grab one of these babys and "play ball."
    "I have not now nor have I ever planned or assisted in the planning of any development or deployment of any kind of device that would be considered a risk to national security."
  16. Mar 24, 2005 #15


    User Avatar

    Staff: Mentor

    Unless there is an asteroid slowly overtaking us nearby, it would take an enormous amount of energy to steer one into orbit. Perhaps in 2029...
  17. Mar 24, 2005 #16
    Perhaps, but for the most part, and there are always exceptons, we are able to detect asteriods on a collision course with earth sometimes years in advance. That considered, the nudge could be quite suttle, short term, and very effective. The size of the engines sent to retrieve the target would not need to exceed the current size of jet engines, and if a bigger nudge is necessary, or if time is of the essence, multiple engines could be deployed. I'm not really a nut case; I've been reading "The Medical Implications Of Nuclear War", published by "The Institute Of Medicine & The National Academy Of Sciences." It only made me wonder, "why we couldn't do just as much destruction without the radiation?" I mean if you have to bring some conflict to an abrupt halt, why contaminate everything in sight for decades? And like the development of the atomic and nuclear devices; "If you'r not first, you could be destroyed." As you know, we've already landed a camera on one asteriod, so actually doing it (grappling onto an asteriod i mean) would be easy. Steering it, with up to dozens of engines if you wish, provides no unworkable issues, - - - - I don't know, we'll see some day. If it can be done, and mankind thinks of it, it will be done. I just hope it's my country does it first. And 2029 isn't that far away that planning couldn't proceed, even at some investigative level. I'm 50. One should not consider this out of reach.
    Just me I guess. Hope I've at least provided an interesting topic.
  18. Mar 25, 2005 #17
    I don't want to lend any support to your idea because either it requires:

    (1) Enormous expenditure of energy (and money and luck to find the asteroid) or
    (2) Very long range planning (small expenditure of energy, many years in advance of use)

    (1) is obviously not going to happen and
    (2) not a good idea. For example, if it had been placed into effect in 1940 to wipe out Japan, where would your game boy come from? :smile:
    More seriously:
    I want to note also that Asian nations are now working on the seventh generation of flat screen displays and the US still can not make in commercial yield quantities the first.

    A few quotes form Physics Today page 30 March 2005 issue:

    (1) "From 1994 to 1998 the number of Chinese, South Korean and Taiwnese students who chose to pursue Ph.Ds in their own countries nearly doubled... and those coming from there to US dropped 19%..." (If more recent data were available, it would be much worse. - The US "terror fear" immigration policy has made the net influx near zero, if not negative. I know of some good Asian professors who have "gone home.")

    (2) "The ratio of college undergraduates degrees in natural sciences is 5.7 per 100 students in the US .... "Taiwan and South Korea each award about 11 per 100." For several other countries listed the ratio ranges between 8 to 13.

    (3) Between 1988 to 2001, East Asian papers in science and engineering have increased by 492% while US production has actually decreased slightly!

    (4) From 1980 to 2001 the US share of worldwide high-tech exports fell from 31% to 18% and China and South Korea's share climbed from 7 to 25%

    Many other sad facts also reported there. More also at www.DarkVisitor.com

    In short, in about one generation US will have lost scientific leadership to Asia. It has already lost technological leadership. No US based firm can even begining to think of making a humanoid looking robot walk while playing a bugle as was recently demonstrated in Asia. In one generation your choice of jobs will be limited to those that can not be exported, like cutting someone's hair or serving fast food. You may not know it but there is a good chance your recent X-ray was interpreted by an India doctor during the night while you slept and his report was back in your US doctor's office the next AM. Indians not only speak English, are smart, well educated, work for less, etc. but they also work while you sleep. Part of the software I am now using was produced there. US is "going down the tubes" and does not realize it.

    Fortunately there is no need to worry about US using your idea - It will soon lack the capacity. US can not even afford to save Hubble telescope!
    Last edited: Mar 25, 2005
  19. Apr 4, 2005 #18
    O. K. - - - Let us start with this; "What might the average speed of an asteriod be??"
    You should be able to do some calculations from there, you think?
  20. Apr 5, 2005 #19
    I assume you are interested in the speed it has as it crosses Earth's orbit, but there is no simple answer, especially if you really interested in the speed it would impact Earth if it were to do so. (Same asteroid hitting on the "trailing side" of Earth produces less damage than by hitting on the leading side. (leading and trailing defined by Earth's motion about the sun.)

    If the asteroid were earth crossing and in a slightly elliptical orbit, it would have approximately the same speed as Earth about the sun. Thus there would be an enormous difference between a "leading hit" and a "trailing one" but in both cases, the fall in the Earth's gravity field would add kinetic energy. We can be 100% sure there are currently no large asteroids like this, one could scatter off Mars etc and come into being.

    If the asteroid were in a very elliptical orbit, then as it crosses Earth's orbit it would have much higher velocity. - It needs the extra energy to climb back up the sun's gravitational well when going back to its apogee point.

    hope that helps.
  21. Apr 7, 2005 #20
    Well, - - - :frown: There are certainly more variables to be considered than I could possibly keep straight, but let's start at, what seems to "me" at least, with the most basic piece of information. I know it's all relative, but "is there" an average volocity range we could assign to asteriods; I mean, is there a highest and lowest miles/kilometers per hour we could expect asteriods, in general, and relative to earth of course, to be moving through space :confused: ??
    Being in a N.E. orbit is not relavent as we could reach out far in advance with the proper data. Wouldn't a leading "or" trailing impact still create tremendous damage?? I'm not sure the asteriods original trajectory will be a concern anyway other than to plot a point in space to grab it; and when and where we grab it may depend on where and when you want it to land somewhere. Now back to the point for this post; How much thrust will it require to stop (relitively, of course) an asteriod of predetermined mass traveling at X volocity, and how many engines of what capacity would be required? This requires formulas that I am not schooled on.
    As with any other developmental program in it's infancy, "cost" is not the primary consideration at this time. The question is, "Can we stop an asteriod?"; "Is it within our means???"
    I comprehind completly your last two paragraphs.
    Thanks, we'll see if mankind can muster the horsepower to stop one of these puppys.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Doomsday Asteroid
  1. Harvesting asteroids (Replies: 1)

  2. A big asteroid. (Replies: 0)