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Defending planet Earth

  1. Jun 30, 2016 #1
    Hello people,

    I got a question and please do not understand it as a fake question.

    In theory would it be possible that when it would come to a collision between the earth and a big sized asteroid, huge jet engines placed on different places on earth could bring earth out of orbit and then after the asteroid has passed the earth without any problems bringing earth then back to correct orbit again ?

    Thanx !

  2. jcsd
  3. Jun 30, 2016 #2


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    No, that wouldn't work or even make any sense. It would be far easier to move the asteroid or blow it up.
  4. Jun 30, 2016 #3
    Mass of the Earth exceeds any conceivable system to move it. Near Earth Objects (NEOs) would be far easier to move. Check Google for various strategies for this.
  5. Jun 30, 2016 #4


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    Take a typical turbo-jet, a General electric CJ805-23B. Even if you covered every square inch of one side of the Earth with them, all their total thrust together would only be enough to move the Earth some 165 km after running them continuously for one week.
    But it is worse than that. They wouldn't actually produce any net movement of the Earth at all. The jet engine throws its exhaust upwards away form the Earth, and you initially get a reaction from the Earth moving the other way. But as the exhaust climbs away from the surface, Earth's gravity pulls back on it slowing its climb. This same gravitational pull slows the Earth's movement in the opposite direction. By the time the exhaust has reached its peak height and begins to fall back to Earth, the Earth has stopped its motion and starts to return to its starting point. They both end up meeting again where they started.
    The only way to produce a net thrust that moves the Earth is for the initial exhaust velocity to be fast enough that the exhaust never falls back to Earth. This equals the escape velocity from Earth or ~11 km/sec. Our best chemical rockets can't produce exhaust velocities of even half of that. So no number of jet or rocket engines mounted on the Earth could move it even an inch.
  6. Jul 7, 2016 #5
    Current Earth government policy would be to ignore the possibility (and eventual probability) of such an impact, argue until it's too late to do anything about it and then go "duh" after the asteroid strikes Earth (assuming there's anyone left to say "duh" at that point.) Never underestimate human arrogance (an asteroid wouldn't dare hit our planet!), superstition (gawd will save us if we just believe in magic), laziness (let the next generation worry about that sort of thing) and (especially) the George Costanza-level cheapness inherent in most governments. Better to spend trillions on massive arsenals of weapons and save cash by cutting space exploration down to nothing. Who cares about space anyway?
  7. Jul 7, 2016 #6
    This episode of PBS Space Time discusses various options.
  8. Jul 7, 2016 #7
    I'm curious as to which governments have this policy.
  9. Jul 8, 2016 #8
    Me too. The US government just funded a complete survey of the sky to find NEOs. After the explosion in Russia, they started creating plans to use their missiles to defend against large asteroids. Considering that there are very few countries that could actually do anything anyway, I imagine that the policy of most nations is "let the Americans and Russians deal with it."
  10. Jul 8, 2016 #9
    No real official policy that I'm aware of, I suppose, just the general tendencies of humanity we see every day. As far as inability or unwillingness to address a problem like that, I think most governments fall into that category. We still have people that deny global climate change, the Apollo moon landings and evolution. I don't think it's a stretch to imagine human arrogance and ignorance putting a damper on a response to an impending collision until it's too late.
    But that's just my pessimistic opinion.
    I agree with you. Venezuela is not going to save the world any time soon. Hopefully something as important as that could get through Congress in time.... hopefully. I too heard that they were "starting plans." Let me know when they're actually finished and are ready to go. Hopefully those plans don't come under budget cuts ("no asteroid out there today, so let's save some money!") They've been whittling down space exploration even more lately.
    That said, necessity is the mother of invention, so an impending impact would be likely to spur quick action. Trouble is, even with their sky survey, there's a lot of elusive objects out there. A lot of the time the first clue to their approach is when they burn through the atmosphere. In that case, the aforementioned "duh" conclusion would be more likely. While I respect your points, I think the two of you have more faith in humanity than I do.
    Last edited: Jul 8, 2016
  11. Jul 8, 2016 #10
    Thanx for info. I like the option of Graffiti! :)
    Ok let us think about of an even worse problem that now a planet sized object is on collision course to earth.
    Is there any chance to prevent the impact of another planet sized object with the options mentioned in the video ?
    Thanx again!
  12. Jul 8, 2016 #11
    Doubtful that a planetary body could be diverted, but that depends on a lot of factors. What's the offending planet composed of? In any event, the best option in that scenario would be to flee Earth altogether and take up residence elsewhere. I think that's more credible than trying to avert a planetary collision.
  13. Jul 8, 2016 #12
    How many people could we get to Mars right now, and how long could they live there without support from Earth?
  14. Jul 8, 2016 #13
    I'm not sure an emergency of this scale would require the Congress. It'd be a matter of national security. I would think the president would declare a state of emergency and use the military for whatever is necessary. He needs congress to declare war, not handle natural emergencies. Even if for some reason there were legal hurdles for Obama, I doubt Putin would have the same hurdles, or would care.
  15. Jul 8, 2016 #14
    None. Humans neither have the rockets or the ships for such a mission. We don't have the capability to go to the moon right now, our current rockets just aren't powerful enough.
  16. Jul 8, 2016 #15
    Congress would, of course, be jostling his elbow. Was ever thus.
  17. Jul 11, 2016 #16
    True. Hopefully bureaucracy could be cut out in a situation that grim. If it was detected in time by a fully funded sufficiently advanced program.
    Therein lies the rub, my friend. Victory loves preparation. The current rockets won't do against an impending impactor, so something new would need to be constructed. You'd need some pretty serious lead time to successfully rush something like that into production. Hurrying in the case of space travel has not always served America or Russia very well in the past. The Apollo 1 astronauts were, in a sense, victims of a program that was going too fast and cutting corners. The Soviet Nedelin Catastrophe is a great example of how short cuts create danger in such situations. Even poor Matt Damon was screwed over by his supply rocket blowing up (although the stated reason for said fictional rocket exploding was dubious). ;)
    I hope that detection and prevention are getting the attention they deserve. I hope that events like what happened in Moscow have gotten the serious attention of politicians. However, I still have very little faith in politicians and even less confidence in practical government spending. Hopefully we'll never have to find out in real life.
  18. Jul 11, 2016 #17
    Here's the thing though, in defense, you don't need to send people. We do have the rockets to send large objects into deep space, they just aren't safe enough for a human crew. With huge amounts of money, prototypes can also be completed very quickly. If the government gave Elon Musk a few billion dollars and told him to get the Falcon Heavy lift vehicle ready in a month, they'd probably be able to do it. It wouldn't be very safe, but it'd certainly be safe enough for a warhead. And in an emergency situation, if for some reason a human needed to go, the military is not above putting pilots at risk to get the job done. The odds of intercepting an asteroid in an prototype would probably be about the same as fighting the Nazi Luftwaffe for nine months.
  19. Jul 12, 2016 #18
    Then why do NASA probes always have to use gravity assists to fling our probes to the outer solar system? Not trying to be difficult there, just actually curious.
    For that to even come close to fruition, you must first have that month. Objects like the one over Moscow were not detected while in "deep space"; people didn't know about them until they were already in the atmosphere. Most of the events of this type to date have not been detected in advance. Too late for Mr. Musk to save the day in those scenarios. Detection must be thorough and constantly funded. Budget cuts continue to plague space endeavors to this day, which makes me skeptical. Governments prefer to spend their money on weapons that kill other people, not theoretical space rocks. Planning ahead isn't necessarily a strong suit for humanity.
    I still stick to my original outlook - in the space rock vs Earth government contest (at least at present) the space rock is going to hit the Earth most of the time. I guess it boils down to the old James Branch Cabell quote with me - "The optimist proclaims that we live in the best of all possible worlds; and the pessimist fears this is true." While Cabell chose neither, I am in the pessimist group.
  20. Jul 12, 2016 #19
    There is an extremely good chance that we'll see the object coming with way more than a month's warning. The object that hit Russia was a few meters across. It was dangerous, but not a threat to the country. Larger objects would be detected by IR surveys that are constantly sweeping the sky. Detection is cheap and is constantly being funded. All it takes is a big IR telescope and some computer software.

    Gravity assist simply makes it easier and way faster. Our rockets are capable of throwing objects out pretty far. If we had to, we could probably send a probe to Mars in a straight shot, it's just faster to fling it around the earth a few times.
  21. Jul 12, 2016 #20
    I learned back in 1970 that it's the one you don't see that gets you.
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