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Someone once broke my brain about hostile alien movies. They said if the aliens were here to take, they could stay in the Oort Cloud or outer planets where the

Someone once broke my brain about hostile alien movies. They said if the aliens were here to take, they could stay in the Oort Cloud or outer planets where the gravity well is shallow, and strip mine our system for natural resources and we wouldn’t even be able to throw anything that high to stop them. We could just watch and shake our fists as they steal our future at their leisure. They wouldn’t even have to send their people. They could use robots on ten systems at once.

ceejayoz 2y ago
> we wouldn’t even be able to throw anything that high to stop them Worse, they could throw bits of the Oort Cloud at us.
- hinkley 2y ago
  When you’re standing at the bottom of a well, don’t mouth off to the person standing at the top.
- ridgeguy 2y ago
  It takes just as much ∆V to throw a rock from the Oort cloud to Earth as to throw the same rock from Earth to the Oort cloud. The aliens don't get an energy advantage by holding the high ground.
  - ceejayoz 2y ago
    > It takes just as much ∆V to throw a rock from the Oort cloud to Earth as to throw the same rock from Earth to the Oort cloud. Yes, but they clearly have the capability to get to the Oort Cloud, and we (other than a small probe) do not. Having the high ground (both physically and technologically) makes holding the Oort Cloud a pretty good spot to be in. (It also takes substantially less ∆V to nudge an existing rock into a nastier trajectory, and we're essentially a big easy to hit static target.)
  - lazide 2y ago
    No it doesn’t, at all. The whole point of the high ground is someone just needs to ‘drop’ something in, which is cheap and easy, but someone on the ‘low ground’ needs to make up all the energy to get up there before they are even at the same level. The energy involved in de-orbiting something and dropping it to the surface of earth (at very high speed) is orders of magnitude less than it would take to get the same mass to even earth orbit from the surface. Holding a brick over the opening of a well is a much more credible threat to someone at the bottom, than that someone with the same brick threatening to throw it back out.
    - Anotheroneagain 2y ago
      That logic doesn't apply to orbital mechanics. The atmosphere is used to brake when satellites are deorbited.
      - lazide 2y ago
        Huh? All you need is for orbits to intersect with the surface, not for a zero velocity vector at the surface. That is far cheaper to do than getting to orbit in the first place. This absolutely applies to orbital mechanics. Atmospheric braking makes it less likely to punch a hole in a skyscraper in manhattan when de-orbiting. And defacto raises ‘the surface’ in some senses. It doesn’t change that it’s far ‘cheaper’ to go down a gravity well than go out of one. Though that atmospheres (and liquid oceans) exist at all does prove exactly the point that I am talking about. The Sun and planets too, come to think of it. If it was cheaper to ‘get out’ than ‘fall in’, none of those could exist. Edit: I used a Hohmann transfer orbit calculator, and from an orbit of ~200km above sea level to an orbit intersecting ground level (0km), it only takes 203 m/s. Without an atmosphere, it would be quite a show of course. But in this situation, that’s the point isn’t it?
        Tronno 2y ago
        You fundamentally misunderstand the concepts. The other poster is correct. Given two orbits, it takes just as much energy to get "up" as it does to get "down".
  - perihelions 2y ago
    That's not actually true; it's an asymmetric problem. You're asking about impacting another orbiting object with nonzero relative velocity. That's not the symmetric question of transferring between two orbits A and B, both ways; it's the asymmetric question of going from orbit A to "some orbit that intercepts B at some point". It's much less delta-v to go from the Oort cloud to Earth—to a highly-eccentric orbit that intercepts the Earth's orbit, without matching its velocity.
ianburrell 2y ago
The first valuable thing on Earth is life. Life may be rare enough, or diverse enough, that worth sampling the unique life on Earth. The intelligent monkeys can be useful, but can be knocked down is cause problems. The second valuable thing is intelligent life. The intelligent monkeys are worth preserving and talking to. But their advanced civilization has lots of potential dangers so need controlling protectorate. The third valuable thing is better minerals. The active processes of the Earth concentrates minerals. They could grind up a whole asteroid, but cheaper to take from Earth. Also, biologic processes make minerals; vacuuming up coal is cheaper than making it. These wouldn't be whole civilization but pirates grabbing some cheap loot before the authorities and natives notice. The fourth valuable thing is Earth itself. Inhabitable planets are rare. The expected way would be apocalypse or annihilation. But I think it would be more interesting to have alien invasion where they ignore us. They settle the arctic, and don't do anything until attacked. Then they start removing CO2 until the temperatures drop and ice age returns.

ceejayoz 2y ago

> we wouldn’t even be able to throw anything that high to stop them Worse, they could throw bits of the Oort Cloud at us.

hinkley 2y ago
When you’re standing at the bottom of a well, don’t mouth off to the person standing at the top.
ridgeguy 2y ago
It takes just as much ∆V to throw a rock from the Oort cloud to Earth as to throw the same rock from Earth to the Oort cloud. The aliens don't get an energy advantage by holding the high ground.
- ceejayoz 2y ago
  > It takes just as much ∆V to throw a rock from the Oort cloud to Earth as to throw the same rock from Earth to the Oort cloud. Yes, but they clearly have the capability to get to the Oort Cloud, and we (other than a small probe) do not. Having the high ground (both physically and technologically) makes holding the Oort Cloud a pretty good spot to be in. (It also takes substantially less ∆V to nudge an existing rock into a nastier trajectory, and we're essentially a big easy to hit static target.)
- lazide 2y ago
  No it doesn’t, at all. The whole point of the high ground is someone just needs to ‘drop’ something in, which is cheap and easy, but someone on the ‘low ground’ needs to make up all the energy to get up there before they are even at the same level. The energy involved in de-orbiting something and dropping it to the surface of earth (at very high speed) is orders of magnitude less than it would take to get the same mass to even earth orbit from the surface. Holding a brick over the opening of a well is a much more credible threat to someone at the bottom, than that someone with the same brick threatening to throw it back out.
  - Anotheroneagain 2y ago
    That logic doesn't apply to orbital mechanics. The atmosphere is used to brake when satellites are deorbited.
    - lazide 2y ago
      Huh? All you need is for orbits to intersect with the surface, not for a zero velocity vector at the surface. That is far cheaper to do than getting to orbit in the first place. This absolutely applies to orbital mechanics. Atmospheric braking makes it less likely to punch a hole in a skyscraper in manhattan when de-orbiting. And defacto raises ‘the surface’ in some senses. It doesn’t change that it’s far ‘cheaper’ to go down a gravity well than go out of one. Though that atmospheres (and liquid oceans) exist at all does prove exactly the point that I am talking about. The Sun and planets too, come to think of it. If it was cheaper to ‘get out’ than ‘fall in’, none of those could exist. Edit: I used a Hohmann transfer orbit calculator, and from an orbit of ~200km above sea level to an orbit intersecting ground level (0km), it only takes 203 m/s. Without an atmosphere, it would be quite a show of course. But in this situation, that’s the point isn’t it?
      - Tronno 2y ago
        You fundamentally misunderstand the concepts. The other poster is correct. Given two orbits, it takes just as much energy to get "up" as it does to get "down".
- perihelions 2y ago
  That's not actually true; it's an asymmetric problem. You're asking about impacting another orbiting object with nonzero relative velocity. That's not the symmetric question of transferring between two orbits A and B, both ways; it's the asymmetric question of going from orbit A to "some orbit that intercepts B at some point". It's much less delta-v to go from the Oort cloud to Earth—to a highly-eccentric orbit that intercepts the Earth's orbit, without matching its velocity.

ianburrell 2y ago

The first valuable thing on Earth is life. Life may be rare enough, or diverse enough, that worth sampling the unique life on Earth. The intelligent monkeys can be useful, but can be knocked down is cause problems. The second valuable thing is intelligent life. The intelligent monkeys are worth preserving and talking to. But their advanced civilization has lots of potential dangers so need controlling protectorate. The third valuable thing is better minerals. The active processes of the Earth concentrates minerals. They could grind up a whole asteroid, but cheaper to take from Earth. Also, biologic processes make minerals; vacuuming up coal is cheaper than making it. These wouldn't be whole civilization but pirates grabbing some cheap loot before the authorities and natives notice. The fourth valuable thing is Earth itself. Inhabitable planets are rare. The expected way would be apocalypse or annihilation. But I think it would be more interesting to have alien invasion where they ignore us. They settle the arctic, and don't do anything until attacked. Then they start removing CO2 until the temperatures drop and ice age returns.