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Survivable change to the earth’s orbit

  1. May 8, 2013 #1
    I would like to know in what ways the earth’s orbit might be modified by the close approach of a massive body from beyond the solar system, such as an orphan earth, Jupiter, super Jupiter planet or brown dwarf.

    The “variables” of interest being the amount of warning we would receive by virtue of the size/luminosity of the approaching body, the degree to which the orbit could be changed and the level of disruption to human civilization.

    Of particular interest are scenarios that drastically change the orbit but do so in such a way that avoids extreme devastation to human civilization during the “fly by” phase of the encounter (notwithstanding the devastation that would undoubtedly occur later due to dislocation of the planetary weather systems to name but one effect ).

    Is a short warning / large event possible or would all such events be spotted decades/centuries in advance?
     
  2. jcsd
  3. May 8, 2013 #2

    mfb

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    We had some discussion about that here and here.

    The general trade-off:
    - more massive objects are easier to spot, this is true even for black holes
    - lighter objects have to pass closer to influence the orbit, this increases tidal forces a lot

    Primordial black holes with a mass somewhere between Jupiter and the Sun should be able to change the orbit of earth significantly with a single fly-by and they are hard to see if they just fly through our galaxy, but none have been observed so far. Without them, it is hard to construct scenarios with less than 100 years of warning time. Gaia will make this even harder.
     
  4. May 9, 2013 #3
    How much force would it take a rapidly moving mass such as the earth to change its orbit without colliding?
    I seriously doubt anything that powerfull would leave anything other than microbes sheltering under the permafrost.
     
  5. May 9, 2013 #4
    Thanks mfb. The links posted above provide a wealth of detailed information and discussion concerning this topic. I have just spent an hour reading through them and their sub links, including 2 research papers and a link to an online gravitational simulator. Well worth the read if the topic interests you.

    Judging by what I have read so far, it is entirely feasible that the earth’s orbit could be drastically changed or the earth could even be ejected from the solar system by an encounter with a suitably massive object passing through the solar system. It is also possible that the encounter would not cause any serious tidal effects.

    That said the devil is in the detail. If the object was too massive or the encounter too close, the resultant tidal effects could disrupt the entire plant or lead to massive tectonic and tidal devastation. On the other hand at too great a distance or too small a mass the encounter might only result in minor disturbance. A sort of 'inverse Goldilocks' distance and mass would be required.

    In terms of the amount of warning; at the very least we can expect 50 years and more probably many hundreds of years. This is even true if the object is a small black hole of say 3 solar masses. Which leads me to ask a further question not touched in the other threads:

    How far back in time would we have to go before the approach of a brown dwarf would go unnoticed until we only had 10 years warning? And how far back before there would be no warning at all?

    There was also some interesting speculation concerning the possibilities of survival of humanity in some form of artificial subterranean habitat in a world devoid of sunlight. I think this would be an good topic to expand upon. It raises interesting questions concerning recycling and artificial semi closed environments. Could a human civilization of some sort exist on a world largely intact but removed from the sun?
     
  6. May 9, 2013 #5

    Ryan_m_b

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    See these two threads:
    https://www.physicsforums.com/showthread.php?t=625503
    https://www.physicsforums.com/showthread.php?t=637311

    Essentially the problem is even more complicated than it looks. Creating a sustainable closed ecosystem would be a huge technological challenge. This would require a high-tech industry to support which means a greater than modern capability but all fitting under one roof rather than spread across the globe. This in turn requires a large labour force of specialised workers which means that the ecosystem has to be big enough to support a high carrying capacity for humans.

    TL;DR the classic science fiction idea of a small group of survivors roughing it in a cave with some hydroponics is far too simplistic. More like such an effort would resemble a multi-million inhabitant ecocity with an industrial capacity to rival that of a small nation today.

    For further reading this blog post by a Sci-Fi writer deals with a related topic and is quite informative: http://www.antipope.org/charlie/blog-static/2010/07/insufficient-data.html
     
  7. May 9, 2013 #6

    mfb

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    For black holes, if they do not have anything nearby, I think everything before SDSS, 2MASS, Hipparcos, and similar scans on should work for a warning time of less than 4-5 years. 1980?

    The discovery of solar-system objects can give hints how likely the discovery of a visible object is and was. Pluto was discovered in 1930, after years of search in specific regions of the sky (as its existence and probable location was predicted from the orbit of Neptune). Any object of similar brightness could have been missed at that time. For a cold object of the size of Neptune, this corresponds to ~2 times the orbital radius of Pluto. With 40km/s relative velocity, this gives less than 10 years.


    @Ryan_m_b: Don't underestimate humans. Our current economy is not designed to work with small groups of humans because it does not have to. As an example, you do not need thousands of workers to produce various plastic parts. You can use a 3D printer. It is more expensive per part, but you just need one person to operate it.
     
  8. May 12, 2013 #7
    It’s interesting to read the other threads in this area where the topic has been at least partly explored. However there did seem to be an emphasis on whether it was possible to build the habitat or not and the time span that would be required (5-50 years). I would suggest that it would be entirely feasible to build, the key point is how long would it last? The more sophisticated the recycling the longer it would survive for. Would it last a few years, a generation, dozens of generations or reach a steady state limited only by the presence of geothermal energy?

    Take just one aspect the light needed to grow crops. This requires power generation, steam turbines, transformers, cable, electric lighting etc (unless anyone can think of a better way of generating light). All of these things will need maintenance and replacement. For instance the electric light source bulbs/ tubes. They might be able to stock pile enough for a few hundred years but eventually these will have to be made and this requires a whole load of other types of technology and equipment which themselves ultimately will have to be maintained and replaced.

    Assuming it was constructed, I wonder what the biggest issue would be? Access to enough electric power? Excess non-recyclable / contaminated waste? insufficient manpower? Mental instability / social unrest?
     
  9. May 12, 2013 #8
    I am amazed that the time frame would become so short quite so quickly going back in time, although you may well be right. If this was the case which probe/event would have been likely to produce the "Oh my God" moment?
     
  10. May 12, 2013 #9

    mfb

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    An astronomer, looking at photographs or through his telescope, and comparing this to previous observations.
    You need several observations of the object to see its motion, and parallax measurements (which need time) to observe its distance.
     
  11. May 13, 2013 #10
    I don't know what you are reading but that comes under the heading of science fantasy.
    No - it is not possible.
    Anyone telling you different is wrong.
    But the tidal effects would be the very least of your problems.
    Of course if it managed to survive as a solid ball and if it managed to land in an orbit within
    the sweet zone somewhere else (both of which are mathematically so close to impossible
    as to make the difference negligible) then it might be possible for the surviving microbes
    to regenerate the planet in say - 5million years there could be sentient life again. Assuming
    some of the water hadn't evaporated off and the ball of rock could somehow retain
    enough of it (that part at least may be possible).
    Of course the very existance of all the water on the planet in the first place is still something of a mystery and its source by no means absolutely certain as yet. So it had better retain water somehow for even the optimistic scenarion above to be viable.
     
  12. May 13, 2013 #11
    Where does the plastic come from.
    Where do the materials the printer is made from originate
    Where does the electricity needed to power it come from
    Where do the spare parts come from
    And what are you going to make thats worth printing on a 3D printer in such a society?
    Cogs for toy robots? Replacement ball point pens?
    Most people are farmers now given this scenario and need to work night and day just to survive -
    growing food would be hard enough - everything else becomes luxury.
    When civilisations fall the first thing lost is advanced technology as the books are burnt to keep the caves warm. (Speaking figuratively there in case it gets missed)
     
  13. May 13, 2013 #12

    Bandersnatch

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    Huh, that's a bold and unsubstantiated statement.

    Of course it's possible.

    A Saturn-size mass passing within a million kilometres from the Earth in front of its orbital path would boost Earth's orbital speed by the extra ~12km/s needed to escape the solar system in mere ~12 hours. (unless I borked my calculations, heh)
     
  14. May 13, 2013 #13
    It is important to be clear about what is being claimed to be possible here.
    1) Could the earth be ejected from the solar system by an encounter - YES it is possible
    2) Could the earth avoid suffering destructive tidal forces in the process - YES it is possible
    3) Would human civilization survive in its current form - No 99.9% of life would die within years

    The question is how long could some form of human subterranean habitat survive for? Years? Decades? Centuries? longer?

    Given that the earth is being ejected from the solar system and away from the sun the fate of the oceans will be to freeze slowly from the top down rather than evaporate.
     
  15. May 13, 2013 #14
    3D printers may well have a part to play, but the real question concerns recycling. Can an enclosed habitat be made sufficiently self sufficient by recycling to allow life to continue? Or how long before the recycling systems breakdown and the repair capacity is degraded?

    Obviously all materials initially present would have been manufactured using the existing facilities on earth before the encounter. After that when life becomes impossible above ground there are 3 possibilities, use stockpiled materials (limited time frame), recreate it from recycled materials (the preferred solution where ever possible) or, dig it out of the ground and make it from scratch (very difficult with a few exceptions). The electricity could come from geothermal power supplemented by nuclear in the short term (decades).

    "When civilisations fall the first thing lost is advanced technology" - a lot of technology would be lost but some would be essential to survival in these circumstances. Light would be needed to grow food, almost certainly electric light. That would mean generators, transformers, steam turbines and enough secondary kit to repair, refurbish and recycle those items.
     
  16. May 13, 2013 #15

    mfb

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    You are adding a lot of requirements not present in the problem statement. Who said that earth should land somewhere else apart from interstellar space, or recover on its own?

    Where does plastic come from: Mainly recycling of old plastic (apart from wear-off, 3D-printers can be very efficient in that respect). The printer can print its own spare parts, this has been demonstrated with existing printers. The only non-printable parts are electronics. To counter wear-off, plastics can be gained from biomass, or chemically from carbon, hydrogen and oxygen. Three elements present in the environment, and three elements you do not want to lose anyway.

    A 3D-printer can be powered by any energy source - geothermal energy looks interesting, but if you have enough biomass burn this, or use humans.

    What do I not make, apart from food, electronics and metal tools?
     
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