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The other planets formed from material in the same nebula (cloud of gas and dust) that collapsed to form the sun. The idea here is this planet would have been m

The other planets formed from material in the same nebula (cloud of gas and dust) that collapsed to form the sun. The idea here is this planet would have been moving through the interstellar medium and just happened to pass close enough to the sun’s gravity well to get captured in a (very distant) orbit.

01HNNWZ0MV43FF 1y ago
Capture would be like a reverse gravitational slingshot? This planet happened to meet the sun at an angle where it lost enough energy to fall into orbit instead of slinging back out like those comets that come around on long cycles?
- tough 1y ago
  gravitational capture
- marcosdumay 1y ago
  AFAIK, it could be in a 2 bodies slingshot, multi-body interaction with some other stuff on the Oort cloud, or tidal interaction (what could happen way more easily with a nebula).
- noah_buddy 1y ago
  A comet coming back on a long cycle is an orbit
- s1artibartfast 1y ago
  You don't need to lose energy to enter orbit any more than you need to lose energy too roll a ball down a hill.
  - tliltocatl 1y ago
    Not true. An obit is not an infinite "plain" with a finite "hill" on but rather a finite "valley". The ball will exit the valley on the other side unless it loses excess kinetic energy somewhere in the valley.
    - s1artibartfast 1y ago
      Correct, but my point is you don't need to lose energy to enter orbit. You don't need complex reverse slingshot interactions. You just need a low enough relative velocity to not shoot off the other side. I would expect this to be the norm for capture, not some exotic phenomenon. A ball doesn't need to lose energy to be captured in a valley either. You just apply a radial force to turn a line into a circle. Anything that approaches the sun slower than escape velocity will be captured.
      - dotancohen 1y ago
        To all other readers: this is wrong.
      - ars 1y ago
        That is not true. If it approaches with less than escape velocity it will gain all the velocity necessary to escape in the process of approaching the Sun. You could think of it as speeding up as it falls toward the sun, it then slows down by the exact same amount as it leaves the Sun. In order to stay near the sun it needs to lose some of that speed, and given that momentum is conserved, the only possible way is to either hit the Sun or send that momentum to a third object.
      - tliltocatl 1y ago
        Anything that approaches the sun will do so with faster than escape velocity because the gravitational potential energy gets converted into kinetic during the approach. Newtonian mechanics is time-reversible - just like it's impossible for an object in orbit to spontaneously escape without gaining energy from somewhere first, it's impossible to enter orbit without losing energy to another body.
        manwe150 1y ago
        Small nit: this is for objects approaching from infinity in a two body system. Otherwise the object can be in orbit and already be “captured” there. For example, the moon also approaches earth slightly over the month while speeding up, then slows down while moving away. Or it could just be a 3 body system, which is chaotic and can’t be modeled accurately and can have objects spontaneously eject from the stable system (even though the physics is indeed reversible)
  - AngryData 1y ago
    But a ball needs to lose energy to not roll right back up a hill to the same height it came from. And if that "ball" is a mass from outside our solar system, it will roll right back out of the solar system just as easily as it rolled in unless there is enough forces to slow it down enough to capture it.
- btilly 1y ago
  It would be like a reverse gravitational slingshot, in a different way. There is no way to capture with just 2 bodies - it would have to leave on gthe same hyperbolic orbit that it arrived on. However if it drove by and had a close enough interaction with a third body, like Jupiter, it could lose angular momentum to the planet, resulting in entering an orbit around the Sun. Further gravitational interactions with planets could then smooth that orbit out over time. Alternately this could be the more straightforward scenario of interstellar object hits planetoid, they merge, and the new combined object is now in orbit.

01HNNWZ0MV43FF 1y ago

Capture would be like a reverse gravitational slingshot? This planet happened to meet the sun at an angle where it lost enough energy to fall into orbit instead of slinging back out like those comets that come around on long cycles?

tough 1y ago
gravitational capture
marcosdumay 1y ago
AFAIK, it could be in a 2 bodies slingshot, multi-body interaction with some other stuff on the Oort cloud, or tidal interaction (what could happen way more easily with a nebula).
noah_buddy 1y ago
A comet coming back on a long cycle is an orbit
s1artibartfast 1y ago
You don't need to lose energy to enter orbit any more than you need to lose energy too roll a ball down a hill.
- tliltocatl 1y ago
  Not true. An obit is not an infinite "plain" with a finite "hill" on but rather a finite "valley". The ball will exit the valley on the other side unless it loses excess kinetic energy somewhere in the valley.
  - s1artibartfast 1y ago
    Correct, but my point is you don't need to lose energy to enter orbit. You don't need complex reverse slingshot interactions. You just need a low enough relative velocity to not shoot off the other side. I would expect this to be the norm for capture, not some exotic phenomenon. A ball doesn't need to lose energy to be captured in a valley either. You just apply a radial force to turn a line into a circle. Anything that approaches the sun slower than escape velocity will be captured.
    - dotancohen 1y ago
      To all other readers: this is wrong.
    - ars 1y ago
      That is not true. If it approaches with less than escape velocity it will gain all the velocity necessary to escape in the process of approaching the Sun. You could think of it as speeding up as it falls toward the sun, it then slows down by the exact same amount as it leaves the Sun. In order to stay near the sun it needs to lose some of that speed, and given that momentum is conserved, the only possible way is to either hit the Sun or send that momentum to a third object.
    - tliltocatl 1y ago
      Anything that approaches the sun will do so with faster than escape velocity because the gravitational potential energy gets converted into kinetic during the approach. Newtonian mechanics is time-reversible - just like it's impossible for an object in orbit to spontaneously escape without gaining energy from somewhere first, it's impossible to enter orbit without losing energy to another body.
      - manwe150 1y ago
        Small nit: this is for objects approaching from infinity in a two body system. Otherwise the object can be in orbit and already be “captured” there. For example, the moon also approaches earth slightly over the month while speeding up, then slows down while moving away. Or it could just be a 3 body system, which is chaotic and can’t be modeled accurately and can have objects spontaneously eject from the stable system (even though the physics is indeed reversible)
- AngryData 1y ago
  But a ball needs to lose energy to not roll right back up a hill to the same height it came from. And if that "ball" is a mass from outside our solar system, it will roll right back out of the solar system just as easily as it rolled in unless there is enough forces to slow it down enough to capture it.
btilly 1y ago
It would be like a reverse gravitational slingshot, in a different way. There is no way to capture with just 2 bodies - it would have to leave on gthe same hyperbolic orbit that it arrived on. However if it drove by and had a close enough interaction with a third body, like Jupiter, it could lose angular momentum to the planet, resulting in entering an orbit around the Sun. Further gravitational interactions with planets could then smooth that orbit out over time. Alternately this could be the more straightforward scenario of interstellar object hits planetoid, they merge, and the new combined object is now in orbit.