Results 1 to 8 of 8

Thread: Do solar wind particles fall back into the solar system?

  1. #1
    Join Date
    Dec 2004
    Location
    UK
    Posts
    8,919

    Do solar wind particles fall back into the solar system?

    I read that the escape velocity of the sun is faster than a lot of solar particles.

    So if they don't escape, do they fall back in? I guess they do....do they fall back at the same rate as the flew out, I mean increasingly fast, and does that count as a kind of solar fall-back wind?
    Formerly Frog march.

  2. #2
    Join Date
    Oct 2005
    Posts
    26,378
    Yes, it is possible for particles to fall back down, and do so all the time-- depending on where you are in the wind (it's less true at large distances, and you also have to worry about the effects of magnetic turbulence that shepherds the particles outward). But the situation is usually treated (for simplicity) in a fluid approximation where you don't worry about individual particles, you worry about the average over a huge number of particles that are moving in all directions. Then you have the concept of a density and an outward velocity of the fluid, and the fluid does not fall back down because pressure forces (forces that appear in the fluid approximation that are not actual forces on the particles) cause the fluid flow to be entirely outward (typically).

    We had a thread recently that claimed gas pressure forces are only forces on walls, so are indeed forces on individual particles and don't happen in the middle of a wind, but that nonsense would make it impossible for you to understand how gas pressure can accelerate a fluid outward without being a force on the individual particles. It's just what happens to the motions of all the particles when you average over a huge distribution of them.
    Last edited by Ken G; 2019-Feb-01 at 06:14 PM.

  3. #3
    Join Date
    Dec 2004
    Location
    UK
    Posts
    8,919
    so if a lot of these solar wind particles fall back, and the net solar wind is away from the sun, then where do these fall-backer particles go?

    Do they end up falling into the gas giants? Or swing around them and end up in orbit around the sun?

    Could this have helped form the gas giants?
    Formerly Frog march.

  4. #4
    Join Date
    Oct 2005
    Posts
    26,378
    They just rejoin the Sun, no help for the gas giants. They don't have enough angular momentum to be in orbit around the Sun, as most fall back from pretty close to the Sun. It's the wind itself that encounters Jupiter, though it's not a large flux of material. The Sun will lose less than a Jupiter mass in the rest of its main-sequence lifetime, and the vast majority misses Jupiter! But when the Sun becomes a red giant, it could lose much more than a Jupiter mass-- but still most of that will miss, and it could as easily peel some mass off Jupiter as add to it.
    Last edited by Ken G; 2019-Feb-04 at 11:17 PM.

  5. #5
    Join Date
    Jun 2005
    Posts
    13,170
    I'm a bit puzzled, and I am sure there must be a reason that I'm overlooking. It says in Wikipedia that solar wind particles leave the corona at about 250 to 700 km/s, and the escape velocity of the sun is about 600 km/s, so a lot of those particles must return. So why is the solar wind moving outward? Shouldn't there be an equal solar wind going back toward the sun?

    Of course, the photons and neutrinos will never return, so there is nevertheless a net outflow of mass (energy) from the sun, but I'm wondering specifically about the charged particles.
    As above, so below

  6. #6
    Join Date
    Mar 2007
    Location
    Falls Church, VA (near Washington, DC)
    Posts
    8,385
    Quote Originally Posted by Jens View Post
    I'm a bit puzzled, and I am sure there must be a reason that I'm overlooking. It says in Wikipedia that solar wind particles leave the corona at about 250 to 700 km/s, and the escape velocity of the sun is about 600 km/s, so a lot of those particles must return. So why is the solar wind moving outward? Shouldn't there be an equal solar wind going back toward the sun?

    Of course, the photons and neutrinos will never return, so there is nevertheless a net outflow of mass (energy) from the sun, but I'm wondering specifically about the charged particles.
    The particles that are accelerated to more than the escape velocity fly away and never return, just as Pioneers 10 and 11, Voyager 1 and 2, and New Horizons are never returning. So yes, the total mass of the Sun is slowly diminishing.

  7. #7
    Join Date
    Jun 2005
    Posts
    13,170
    Quote Originally Posted by Hornblower View Post
    The particles that are accelerated to more than the escape velocity fly away and never return, just as Pioneers 10 and 11, Voyager 1 and 2, and New Horizons are never returning. So yes, the total mass of the Sun is slowly diminishing.
    Of course, I understand that, but Iím asking about the ones that come back. Is there a significant reverse wind?


    Sent from my iPhone using Tapatalk
    As above, so below

  8. #8
    Join Date
    Oct 2005
    Posts
    26,378
    The issue is whether you look at individual particles, or if you make what is known as the "fluid approximation" and average over large collections of particles. When people talk about the "solar wind", they are normally doing the latter, and use language like "density", "temperature", and "gas pressure", none of which make much sense when you look at an individual particle. There is also the fluid parameter "flow velocity", which is generally always outward in the solar wind (though if you look at low-lying collapsing structures like you can have when filaments erupt, you can see downward flow, but that's more like the chromosphere than the wind.) The same issue appears when you go outside on a windy day-- you would say the wind is blowing in one direction, but if you look at any individual air molecule, it is almost as likely to be going in any direction.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •