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>the object might be the rocket booster of Surveyor 2, a robotic spacecraft that was launched to the moon on September 20, 1966. When imaginative theorists spe

>the object might be the rocket booster of Surveyor 2, a robotic spacecraft that was launched to the moon on September 20, 1966. When imaginative theorists speculate about a previous space-faring civilization, I always wonder about the possibility of space-junk. Wouldn't we have observed their space-junk floating around the earth?

helsinkiandrew 6y ago
It takes a few centuries for anything with less than a 1000km high orbit to have decayed and returned to earth. Assuming that the previous civilisation was many thousands of years ago everything will have burnt up on reentry, crashed into the sea, or been destroyed by the Alien technology that got rid of the last civilisation.
- foota 6y ago
  Lagrange points?
  - helsinkiandrew 6y ago
    Even if the civilisation put something at a lagrange point between earth and the moon, even the slightest momentum would eventually shift the objects out eventually
    - maxerickson 6y ago
      L4 and L5 are stable. https://en.wikipedia.org/wiki/Lagrange_point#Natural_objects_at_Lagrange_points https://en.wikipedia.org/wiki/Lagrange_point#Natural_objects...
      - Elrac 6y ago
        Yes, but that's irrelevant to your parent commenter's point. I'll explain that in simpler terms: If the object has the slightest bit of (linear) momentum then it also has a non-zero velocity, which will over time move it away from said Lagrange point. I'll add that even with zero velocity, the Lagrange points are stable only in an ideal system where the only gravitational influence is from the two bodies between which the Lagrange points sit. An object sitting on a Lagrange point could still be perturbed by attraction from other planets or passing asteroids. Given enough time, no orbit stays stable.
        maxerickson 6y ago
        So how come there are all the natural trojans then?
        jfoutz 6y ago
        There are a few things to keep in mind - and I'm probably forgetting a bunch of important factors. First think about solar wind. light shining provides a real force on everything the sun shines on, not much, but not zero - an 800m^2 sail is about 5 newtons. about as much as holding a full pint glass above the bar, constantly, forever. It takes some effort to overcome that force. Smaller things, smaller forces - but the force is always there. Second, think about a marble in a bowl - the object at the Lagrange point. it'll sit at the bottom of the bowl. but if you constantly move the bowl in little circles the marble will little by little pick up momentum, go a little faster and faster, then start to climb the walls of the bowl. (this is like the sun shining on the object at the Lagrange point. eventually, it'll go so fast the marble gets kicked out. A big heavy ball bearing will take a whole lot longer to pick up that momentum, and may never get enough to escape. I'm not sure how much friction there is in space (or stuff that acts like friction) but I'd believe the big heavy rocks really can't get kicked out by just solar wind, thus natural trojans. Anyway - this is pretty hand-wavy but the math is the same. The sun is constantly applying force, you gotta deal with that somehow. small profile from the point of view of the sun, and high density probably work out great.
        deepsun 6y ago
        No, you're confusing with unstable Lagrange points and Lissajous orbits. Stable Lagrange points have forces that move back the object if it's perturbed. So, perturbed slightly, the object can move around the exact Lagrange point in various ways, but come back.
- lowdose 6y ago
  What if they had black hole bomb capabilities?
hoorayimhelping 6y ago
Yes. But even more than seeing their space junk, we would have seen evidence of them being on earth in the ground. Civilization changes nature, and when looking through nature, it's very easy to see evidence of civilization. It doesn't look like anything else in nature - right angles, straight lines, clean dividing boundaries, and layers of non-natural debris and junk in the fossil record. There is very clear evidence of a massive asteroid impact 65 million years ago, because there is a layer of iridium in the fossil record that didn't exist before and wasn't natural. In 65 million years, evidence of us being here will be expressed in the fossil record as a layer of hydrocarbons (maybe residue from concrete and steel) from all the hydrocarbons we've pulled out of the earth and released back into the environment. It's fun to think about civilizations coming before us, but we're the first terrans to reach the level of technical sophistication so that we can change the world on a global scale. Period.
- goda90 6y ago
  Couldn't it be possible there are layers that we've explained as having natural causes simply because when discovered, those attempting to explain them didn't even consider the idea it was caused by a civilization? We're already seeing life adapt to plastics with enzymes that break them down. Perhaps the layer we leave will look more natural than we're assuming.
- gdubs 6y ago
  NASA scientists published a study on this. It’s not as straightforward as one might think: https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/ https://www.theatlantic.com/science/archive/2018/04/are-we-e... Link to original paper within the article.
fit2rule 6y ago
If we had, would we be willing to discuss it openly with the world cultures as they are? https://en.wikipedia.org/wiki/Black_Knight_satellite_conspiracy_theory https://en.wikipedia.org/wiki/Black_Knight_satellite_conspir...
bpodgursky 6y ago
Objects in high geosynchronous orbits do not meaningfully decay.
nanomonkey 6y ago
Perhaps the moon itself?

helsinkiandrew 6y ago

It takes a few centuries for anything with less than a 1000km high orbit to have decayed and returned to earth. Assuming that the previous civilisation was many thousands of years ago everything will have burnt up on reentry, crashed into the sea, or been destroyed by the Alien technology that got rid of the last civilisation.

foota 6y ago
Lagrange points?
- helsinkiandrew 6y ago
  Even if the civilisation put something at a lagrange point between earth and the moon, even the slightest momentum would eventually shift the objects out eventually
  - maxerickson 6y ago
    L4 and L5 are stable. https://en.wikipedia.org/wiki/Lagrange_point#Natural_objects_at_Lagrange_points https://en.wikipedia.org/wiki/Lagrange_point#Natural_objects...
    - Elrac 6y ago
      Yes, but that's irrelevant to your parent commenter's point. I'll explain that in simpler terms: If the object has the slightest bit of (linear) momentum then it also has a non-zero velocity, which will over time move it away from said Lagrange point. I'll add that even with zero velocity, the Lagrange points are stable only in an ideal system where the only gravitational influence is from the two bodies between which the Lagrange points sit. An object sitting on a Lagrange point could still be perturbed by attraction from other planets or passing asteroids. Given enough time, no orbit stays stable.
      - maxerickson 6y ago
        So how come there are all the natural trojans then?
        jfoutz 6y ago
        There are a few things to keep in mind - and I'm probably forgetting a bunch of important factors. First think about solar wind. light shining provides a real force on everything the sun shines on, not much, but not zero - an 800m^2 sail is about 5 newtons. about as much as holding a full pint glass above the bar, constantly, forever. It takes some effort to overcome that force. Smaller things, smaller forces - but the force is always there. Second, think about a marble in a bowl - the object at the Lagrange point. it'll sit at the bottom of the bowl. but if you constantly move the bowl in little circles the marble will little by little pick up momentum, go a little faster and faster, then start to climb the walls of the bowl. (this is like the sun shining on the object at the Lagrange point. eventually, it'll go so fast the marble gets kicked out. A big heavy ball bearing will take a whole lot longer to pick up that momentum, and may never get enough to escape. I'm not sure how much friction there is in space (or stuff that acts like friction) but I'd believe the big heavy rocks really can't get kicked out by just solar wind, thus natural trojans. Anyway - this is pretty hand-wavy but the math is the same. The sun is constantly applying force, you gotta deal with that somehow. small profile from the point of view of the sun, and high density probably work out great.
      - deepsun 6y ago
        No, you're confusing with unstable Lagrange points and Lissajous orbits. Stable Lagrange points have forces that move back the object if it's perturbed. So, perturbed slightly, the object can move around the exact Lagrange point in various ways, but come back.
lowdose 6y ago
What if they had black hole bomb capabilities?

hoorayimhelping 6y ago

Yes. But even more than seeing their space junk, we would have seen evidence of them being on earth in the ground. Civilization changes nature, and when looking through nature, it's very easy to see evidence of civilization. It doesn't look like anything else in nature - right angles, straight lines, clean dividing boundaries, and layers of non-natural debris and junk in the fossil record. There is very clear evidence of a massive asteroid impact 65 million years ago, because there is a layer of iridium in the fossil record that didn't exist before and wasn't natural. In 65 million years, evidence of us being here will be expressed in the fossil record as a layer of hydrocarbons (maybe residue from concrete and steel) from all the hydrocarbons we've pulled out of the earth and released back into the environment. It's fun to think about civilizations coming before us, but we're the first terrans to reach the level of technical sophistication so that we can change the world on a global scale. Period.

goda90 6y ago
Couldn't it be possible there are layers that we've explained as having natural causes simply because when discovered, those attempting to explain them didn't even consider the idea it was caused by a civilization? We're already seeing life adapt to plastics with enzymes that break them down. Perhaps the layer we leave will look more natural than we're assuming.
gdubs 6y ago
NASA scientists published a study on this. It’s not as straightforward as one might think: https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/ https://www.theatlantic.com/science/archive/2018/04/are-we-e... Link to original paper within the article.

fit2rule 6y ago

If we had, would we be willing to discuss it openly with the world cultures as they are? https://en.wikipedia.org/wiki/Black_Knight_satellite_conspiracy_theory https://en.wikipedia.org/wiki/Black_Knight_satellite_conspir...

bpodgursky 6y ago

Objects in high geosynchronous orbits do not meaningfully decay.

nanomonkey 6y ago

Perhaps the moon itself?