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If there are that many Jupiter+ sized objects then how many rocky planet sized ones are there? Would they even be detectable via infrared or gravitational lensi

If there are that many Jupiter+ sized objects then how many rocky planet sized ones are there? Would they even be detectable via infrared or gravitational lensing?

api 3y ago
I had a thought a while back about interstellar flight: If there are a lot of massive objects out there (rogue planets, maybe primordial black holes) then these could be used to aid acceleration and deceleration through gravity assist and the Oberth effect. (The latter describes how you get more acceleration thrusting near a massive body.) You could fly along with an ultra sensitive gravity telescope / sensor and hop between massive objects. You could also perhaps harvest propellant from some of these. Long duration interstellar flight would be easier if the space between solar systems was not as empty as we think.
- pavel_lishin 3y ago
  I think gravity assists only really make sense when you're talking about orbits - a solitary object floating through the void won't help you accelerate, though it can help you make a cheaper "turn" in space.
  - api 3y ago
    Doesn’t the Oberth effect still work?
    - pavel_lishin 3y ago
      Actually, hm, I don't know. If you're approaching a mass in space, and firing your engine close to it - do you end up with a faster relative velocity than if you'd just fired your engines for the same amount of time in empty space? edit: I did the most basic possible amount of research by reading the first paragraph of the wikipedia article (can we call that a milliHbomberguy?), and you're right, you do gain more velocity than just firing your engine in space. Although it puts a limit on where you'll be going after your approach.
      - api 3y ago
        The Oberth effect is fascinating. It sounds like a violation of conservation of energy but it’s not. You can get multiples of thrust. An Oberth effect flyby of a primordial black hole with a high impulse drive like nuclear pulse propulsion would be pretty spicy. It’s a feasible way to achieve speeds close to the speed of light. Acceleration would kill you though. If we did find such an object anywhere within a few light years of the sun it would be a way to send probes out at significant fractions of the speed of light.
- throwaway4aday 3y ago
  Interstellar travel is only going to work if we're using much more powerful propulsion techniques than we currently are. I don't think gravity assists will help much in that case. I still think it's a boon to have a lot of interstellar bodies though, they are certainly easier to reach than the nearest stars and they could be just as interesting. Who knows what kind of weird, icy worlds might exist out there heated only by radioactive isotopes and tidal forces?
throw83485 3y ago
Not many. Gas giants can form on their own, they have composition similar to interstellar material (mostly hydrogen and helium). Rocky planets can only form in proto disks around newly forming stars. Heavier materials (carbon and up) are concentrated this way.
- throwaway4aday 3y ago
  Well, that entirely depends on if the theory and models being used are correct. This article seems to indicate that many of those beliefs did not match reality. I think we should keep looking rather than discount out of hand. There are more things in heaven and earth, after all.

If there are that many Jupiter+ sized objects then how many rocky planet sized ones are there? Would they even be detectable via infrared or gravitational lensing?

api 3y ago

I had a thought a while back about interstellar flight: If there are a lot of massive objects out there (rogue planets, maybe primordial black holes) then these could be used to aid acceleration and deceleration through gravity assist and the Oberth effect. (The latter describes how you get more acceleration thrusting near a massive body.) You could fly along with an ultra sensitive gravity telescope / sensor and hop between massive objects. You could also perhaps harvest propellant from some of these. Long duration interstellar flight would be easier if the space between solar systems was not as empty as we think.

pavel_lishin 3y ago
I think gravity assists only really make sense when you're talking about orbits - a solitary object floating through the void won't help you accelerate, though it can help you make a cheaper "turn" in space.
- api 3y ago
  Doesn’t the Oberth effect still work?
  - pavel_lishin 3y ago
    Actually, hm, I don't know. If you're approaching a mass in space, and firing your engine close to it - do you end up with a faster relative velocity than if you'd just fired your engines for the same amount of time in empty space? edit: I did the most basic possible amount of research by reading the first paragraph of the wikipedia article (can we call that a milliHbomberguy?), and you're right, you do gain more velocity than just firing your engine in space. Although it puts a limit on where you'll be going after your approach.
    - api 3y ago
      The Oberth effect is fascinating. It sounds like a violation of conservation of energy but it’s not. You can get multiples of thrust. An Oberth effect flyby of a primordial black hole with a high impulse drive like nuclear pulse propulsion would be pretty spicy. It’s a feasible way to achieve speeds close to the speed of light. Acceleration would kill you though. If we did find such an object anywhere within a few light years of the sun it would be a way to send probes out at significant fractions of the speed of light.
throwaway4aday 3y ago
Interstellar travel is only going to work if we're using much more powerful propulsion techniques than we currently are. I don't think gravity assists will help much in that case. I still think it's a boon to have a lot of interstellar bodies though, they are certainly easier to reach than the nearest stars and they could be just as interesting. Who knows what kind of weird, icy worlds might exist out there heated only by radioactive isotopes and tidal forces?

throw83485 3y ago

Not many. Gas giants can form on their own, they have composition similar to interstellar material (mostly hydrogen and helium). Rocky planets can only form in proto disks around newly forming stars. Heavier materials (carbon and up) are concentrated this way.

throwaway4aday 3y ago
Well, that entirely depends on if the theory and models being used are correct. This article seems to indicate that many of those beliefs did not match reality. I think we should keep looking rather than discount out of hand. There are more things in heaven and earth, after all.