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

Asteroid 99942 Apophis impacting the Earth in 2029

  1. Feb 27, 2015 #1
    Good Day everyone! :wink:
    I don't know if this thread is repeated already. Because I cant find one.
    I just want to ask you guys what are your insights for the asteroid apophis' possible impact to earth by 2029? Upon its discovery in 2004, Apophis was briefly estimated to have a 2.7% chance of impacting the Earth in 2029. :nb) :nb) Don't you think we have enough technology to avoid this impact? :wideeyed: :wideeyed:
  2. jcsd
  3. Feb 27, 2015 #2


    User Avatar
    Science Advisor
    Gold Member

    The possibility of apophis impacting earth in 2029 [or 2036] has been virtually eliminated bases on improved data accumulated in 2012 - 2013 - re: http://neo.jpl.nasa.gov/apophis/
  4. Feb 27, 2015 #3

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

  5. Feb 28, 2015 #4

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    Use the search tool. There have been a number of threads on Apophis.

    There's no impact to avoid. Apophis is now deemed a non-threat, both in 2029 and in 2036.

    What about other asteroids? The best defense is time, lots and lots of time. Suppose a 1 km diameter asteroid is on a collision course with the Earth, and we first see it two weeks prior to impact. We're dead. There's nothing we can do. We need time, many years of advance warning. Even then, diverting a 1 km diameter asteroid is a daunting problem. Many are of the opinion that the best option is hitting it with nukes to slightly change the asteroid's orbit. A long period comet is much worse. Now nukes aren't just the best option, they're the only option.
  6. Mar 1, 2015 #5
    Not an expert, but I tend to agree with this. A nuke would be unlikely to split a dino-killer, but even if it did, and only a part of it struck the planet, that would be worth it.

    Actually though, if we DID get sufficient warning (probably more than the necessary notice for bombing the body) to land a nuke-powered machine on the missile, or perhaps match orbits, I bet we could do better than exploding anything, nuke or not.
  7. Mar 1, 2015 #6
    Project Orion will be able to alter the orbit. George Dyson discusses this here.
  8. Mar 1, 2015 #7
    Hey John, THANKS! It wasn't the idea that *I* had, but I loved it all the same, and Dyson's presentation was really entertaining.

    Much appreciated,
  9. Mar 2, 2015 #8
    Apophis, even if missing us, could be very good for raising funds for Space Security programs, currently under-funded all over the world although very important for future safety of the Planet.
    It could also boost asteroid-mining programs, also important for future space missions.

    People wouldn't like to see its money "wasted" to explore/deviate/destroy astreroids millions of kilometers away, in asteroid belt. But I guess people would appreciate using its money to monitor and study Apophis.

    I really hope somebody will successfully land a camera on it before 2029! :-) It would be a big engineering/science achievement. I won't be surprised when a project will appear on Kickstarter for a private mission on Apophis.
  10. Mar 3, 2015 #9


    User Avatar
    Science Advisor
    Gold Member

    If we were serious about diverting an asteroid with a nuclear detonation, which is the only realistic short notice option in the foreseeable future, a test would be the natural first step. Unfortunately, politics is a constraint. Whoever launched such a 'test' would face severe criticism, even to the point of attempting to induce impact on an unfriendly state. The effects of a nuclear blast in the vacuum of space are largely unknown, but, certainly much differently than one in earths atmosphere. The blast wave would be essentially non existent, so it would necessitate detonation very near or at the surface of the target. Material ablated from the target body would serve to provide the blast energy necessary to nudge its trajectory. Unfortunately, detonation at such proximity would likely fragment the target, and not appreciably alter its trajectory, resulting in a 'buckshot' impact. It appears 'testing' will only occur in the face of imminent disaster. I anticipate it will be a very big 'test', should the occasion arise. Existing nuclear weapons are only designed to achieve low orbit trajectories, so some unknown number of extra terrestrial capable rockets probably [hopefully?] already exist for such an exigency.
  11. Mar 3, 2015 #10
    A nuke is totally useless in diverting an asteroid: it has the needed energy, but it acts in all directions. We'd need a "collimated nuclear blast".... which unfortunately has not yet been invented! But we could use nuclear power to power a huge ion engine.
  12. Mar 3, 2015 #11
    There is a new web site I found that seems to still be in the works, but there is some good information on the site. http://www.apophisasteroid.org/ Check it out. From what I read on this website, the Sun could cause out-gassing, causing the asteroid to tumble through space. Nothing is 100% guaranteed, the chance of the asteroid hitting the Earth in 2029 is very small, but the chance of the asteroid hitting Earth in 2036 is much larger.
  13. Mar 3, 2015 #12
  14. Mar 3, 2015 #13
    Hmmmm, It works for me. I tried the link in google and explorer and both worked. Try this www.apophisasteroid.org
  15. Mar 3, 2015 #14


    User Avatar
    Science Advisor
    Gold Member

    naaa that doesn't work either
  16. Mar 3, 2015 #15
    I'm in South Africa and I simply clicked on the link in Inphinity's posting and it worked immediately. You must have something funny about your service provider or your LAN's regulations or firewalls or the like. Check with your admins.
  17. Mar 4, 2015 #16

    Mark Harder

    User Avatar
    Gold Member

    I think we agree that placing a nuke on an asteroid and fracturing it is not a good idea for a variety of reasons. But that leaves open the possibility that we could explode the weapon some distance, to be determined, from the asteroid. The idea is that this would either slow it or speed it up if exploded in front or behind it. Or exploded it at some angle away from the asteroid's path, directly pushing it out of orbit. But that raised other questions, at least to me. By what mechanism would a nuclear explosion in a vacuum exert force at a distance?
    Shock waves, as usually understood, wouldn't exist in a vacuum, or would they? A fireball of outrushing matter would exert frictional forces on an object in its way. But how much matter is released by nuclear explosion? The rest mass of a thermonuclear warhead is not that great, really. So I wouldn't expect one to generate much force, relative to an asteroid's inertia. Radiation in the form of infrared, visible light and gamma rays would exert force as well; perhaps radiation pressure would generate a greater force than a rapidly expanding plasma or a shock wave. Of course, energy and mass not radiated within the solid angle subtended by the asteroid would be wasted. That consideration seems to me to be the most damnable objection to the bomb idea - the extremely small yield of energy from the explosion.
    The only other measure I can think of is placing a rocket of some sort on the asteroid. That way the force exerted on the body would be directed. Knowledge of the asteroid's mass and the force integrated over the lifetime of the rocket's combustion would enable one to calculate both the changes in the asteroid's velocity and its direction over time. When we place satellites in orbit or send vehicles to other planets, these factors must be known to high precision. The success of these missions gives me confidence that the rocket method could succeed. Someone mentioned the Project Orion concept. But isn't the nuclear weapon-powered rocket just a variant of exploding a warhead at some distance from the object? We would still be wasting most of the energy through radiation into empty space. Given the present state of art, how precisely could the force of these mini-explosions be calculated? Haven't we already designed rockets based on electromagnetic propulsion and propulsion provided by the flow of cooling gasses or liquid metals through a fission reactor? Those latter approaches sound the most plausible to me. What do other folks think?
  18. Mar 4, 2015 #17


    User Avatar
    Science Advisor
    Gold Member

    I don't need to check with any admins ..... I'm not the only one it doesn't work for !!
  19. Mar 4, 2015 #18
    Not correct, even allowing for hyperbole in "totally useless".
    1: Even if the uncollimated blast is only 10% effective, if the nuke is ten times the notionally necessary size, that would suffice to justify the venture -- far from useless.
    2: Suppose the nuke were triggered a millisecond before impact at high relative velocity, so that what hits the surface is a small, penetrating, but rapidly expanding fireball. The effect would amount to quite a highly collimated propulsion, with most of the reaction mass supplied by the target's own surface and shallow material. Even if the target fragmented (by no means certain for a largish object), most of its mass would be be accelerated in the desired general direction, though not all equally well or precisely.
    3: Even if the fragmentation amounted to converting a "rubble-pile" object into a shotgun blast, not only would that blast be collimated in a favourable direction, but fine fragmentation would produce essentially a (probably harmless) meteor shower of particles. The effect would be drastically less disastrous than the rubble striking as a pile in a single spot at a single moment, rather than a shower over a few million square km over perhaps a period of some minutes.
    4: Even if the blast neatly split a physically strong and dense missile into just a few large fragments, each too large to be acceptable "incoming", each being far from harmless on striking Earth, then if in fact in fact not all were effectively deflected, the chances are that not all would hit the planet, so the effect certainly would be mitigated by that at least. And even if every last fragment hit Earth with unaltered energy, divided impacts would be less catastrophic than a single large one. To achieve such a lesser disaster would be no means a "totally useless" investment, but a highly profitable or at least provident one.
    5: Even if the cleanly split body left a few large missiles still on target, then if a flotilla of small nukes followed the large nuke by a few days, then in the interval before the trailing flotilla arrived, the trajectories of the major lumps could be measured and calculated with great precision. Surgically smaller nukes could nudge remaining really dangerous rocks the extra mile. Space billiards. No problemo!
    Example: suppose something like our "rubber-duck" Comet 67P/C-G broke its neck when the nuke hit it, it is quite likely that the spinning halves would follow different courses, both missing Earth. But even if one did not miss Earth, the smaller impact would be a worthwhile mitigation. And a flotilla nuke now could tackle the dangerous remnant more surgically. And if there were no significant fragmentation, the smaller nukes could tackle the main body again for further longer-term improvements in prospects.
    6: Gentler nudges could be negotiated in various ways. A series of blasts from space could vapourise part of the missile's surface each in turn till the reaction produced sufficient deflection.
    7: Or the nuke could carry packing in the right orientation for the packing mass (wadding if you like) to be accelerated for impact, but not vapourised by the blast. That wadding then could hit the target at enormous velocity without vapourisation. Such a soggy solid wadding striking the target would amount to a high degree of collimation of blast. The mass of the carrier craft could act as a tamper from behind, or might act as the missile itself. The most probably efficient approach should be left to some intelligent engineer (if the project could afford one; if not, they could always get a lawyer or politician or priest instead... Details, details...)
    8: I bet that a very high degree of collimation could be achieved, though expensively, by including an asymmetrical hollow shell around the nuke, so designed that it vapourises progressively from the far end, driving the target end with great acceleration. Whether this would be worth the extra mass required to deliver to the ignition site, is a different question. Whether such a mass as a missile would be more useful as a reflector or tamper, is also something to be calculated rather than argued.

    It is dangerous to dismiss as absolutely useless any technology that offers wide ranges of modes of possible application. Someone might have worked out more ways of applying it than were at first obvious.
    Last edited: Mar 4, 2015
  20. Mar 4, 2015 #19


    User Avatar
    Science Advisor
    Gold Member

    I think you got the gist of it Mark, a nuke would be ineffective without mass to propagate a shock wave. That mass would have to come from the target, and probably splinter it. My guess is you would need a timed chain of detonations to be effective. But, none of this has ever been attempted, so any such 'solution' is suspect. If, however, you only have a matter of weeks to act, is there any other realistic option? I lean towards the idea of a fleet of space capable missiles lurking in secret silos - assuming we have sufficient foresight, and will, to mount anything resembling a defensive strategy.
    Last edited: Mar 4, 2015
  21. Mar 4, 2015 #20
    Generally reasonable, but we are being peppered by what seem to be very varied masses. They vary in size from a few tens of metres diameter to a few tens of km. Yes, I know there are smaller ones, all the way down to dust, and that the smaller,the very much more frequent, but the impact of anything just tens of metres across would be a local, not a global, emergency unless it were shown to be aiming for Washington DC, Moscow, Beijing, Pyongyang, Tehran, Naypyidaw or the like; some place that no one could tolerate the destruction of and that couldn't be evacuated. Then again, I am sure that solid bodies on the multi-km scale will not be split by a typical nuke, and I am not sure that any but a marginal example could be sufficiently deflected by any nuke less than tens of years in advance.

    Where a nuke would be possible, converting a 10-30 m rock to buckshot would amount to solving the problem, and diverting it shouldn't be a very big deal, so we might nuke it in a hurry if a major city were at definite risk, but for large projectiles say 100m +, we could consider three classes:
    1: Ni-Fe pretty solid mass. Forget it. It won't shatter worth a dam, but might well divert neatly. Anyway, it could be valuable if it landed in the right spot! :)
    2: Pretty solid rock (basalt?) I doubt it would shatter badly, and it might deflect nicely. It would be worth a try for anything too big for us to deflect by other means.
    3: Rubble pile/snowball etc These could present problems. For one thing it would be difficult to determine their actual nature well enough to predict their behaviour. They might deform instead of diverting. However, again, if a pile were shown to be heading unacceptably, we might have to nuke it in the hope that it does largely spall into relatively harmless scattered buckshot instead of striking in a concentrated mass that would for practical purposes amount to a solid projectile.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Asteroid 99942 Apophis impacting the Earth in 2029