Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Dust accumulation and change of weight (or mass, or gravitation field)

  1. Apr 19, 2008 #1
    I was wondering what is happening with earth accumulating dust and other debris from outer space? This must change earth’s weight? What is the rate of this accumulation of weight? The same thing must be happening to the sun, surely in proportion to the gravity field of the sun, so probably all in all the balance of our planetary system is conserved, in spite the fact everything is getting heavier, but heavier than what? The same thing must happen everywhere else as well, so where can I read something about this?
  2. jcsd
  3. Apr 19, 2008 #2
    Let's say that meteor hits the Earth (and doesn't make much damage). Then both meteor and the Earth will act on us and pull us towards them, now with greater force than it was when the meteor was far away in the space. We'll do the same thing to them (according to Newton's 3rd law). So, the force between the Sun and the Earth will also be greater and we'll get a bit closer. It's just the question how big is the mass of the meteor according to the Earth's mass. That defines how "heavier" we'll be.
  4. Apr 19, 2008 #3
    yes, but we do not need a meteor, every day many tones of dust from space settle on earth, I was just wondering how much and how did it effect our trajectory, in the last 300 years since Kepler?
  5. Apr 19, 2008 #4
    Would changing a weight of an object really change it's trajectory that much?

    Jupiter is so much bigger than the Earth, and yet it's much further from the sun, and doesn't seem to fall or get any closer over millions of years.

    The right question (trajectory-wise anyway) would be: "Does this dust change the speed/velocity of Earth in any way?", because velocity is the thing that really defines trajectory.

    And the answer is no.
  6. Apr 19, 2008 #5


    User Avatar
    Gold Member

    Several hundred tonnes of matter impact the Earth every year. It's insignificant.
  7. Apr 19, 2008 #6


    User Avatar
    Science Advisor

    We did an interesting problem like this in our physics class. Even the meteor that impacted the earth and is thought to have caused the extinction of the dinosaurs (among other species) had a negligible impact on both the earth's mass and trajectory.
  8. Apr 19, 2008 #7


    User Avatar
    Gold Member

    Exactly. Getting it all in one chunk like that will have devestating effects upon the atmosphere and crustal activities. Still nothing to affect the orbit, though.
  9. Apr 19, 2008 #8
    What if the Earth's mass increases x2 at an instant, will it fall on the sun, or find a new balance point?
  10. Apr 19, 2008 #9

    the earths orbit around the sun would not be affected that much.

    but the moons orbit around the earth would. it would be a much more eccentric orbit, with the apogee having about the value of its current distance.
  11. Apr 21, 2008 #10
    if what you say is true. then what about the debris the sun collect? is the sun getting heavier? aren't we the "moons" of the sun? shouldn't that affect us eventually?
  12. Apr 21, 2008 #11


    User Avatar
    Gold Member

    The cosmic perception of 'eventually' pretty much means that the sun will have died a natural death long before any effect of infalling matter could be noticed.
  13. Apr 22, 2008 #12
    OK, but are there some calculations of this rate of change(?), or is it just a rule of thumb, for cosmic events?
  14. Apr 22, 2008 #13
    you also have to consider that the sun is loosing mass.

    the first mechanism that is very easy to calculate from first principles is, that because the sun emits energy it has to loose mass (E = mc^2), my result for this is a loss rate of of 4,27 E6 kg/s.

    there are further mechanisms like the ejections of solar flares, but I have not idea how to calculate them.

    I also have to admit that I have no idea how high the rate of dust accumulation is, and whether the net effect is mass gain or loss.

    and yes, a change of the suns mass would affect the earths orbit, but as Danger said, we are talking about a real long time here.
  15. Apr 22, 2008 #14
    Sun is losing hundreds of tons of mass in prominences every day.
    What will affect us eventually is the cooldown of the sun in a few billion years, when it will expand, consuming all planets before the asteroid field (I think?)
  16. Apr 22, 2008 #15
    it will become a red giant one day, thats for sure, I just dont remember how much it will expand then
  17. Apr 23, 2008 #16
    Perhaps for some reason or other there is a wonderful correlation between the gaining and loosing of mass in the sun. That will makes the sun much more stable than we realize?
  18. Apr 23, 2008 #17
    No mattert how much dust you pound on the sun, the amount of hydrogen will not increase.
  19. Apr 26, 2008 #18
    apologies that it took me so long to realize this - what I wrote in post #13 is not completely wrong, but it misses the most important point: the sun is not a "dust sucker" at all, on the contrary, dust particles are pushed away from the sun by radiation pressure and the solar wind ! the tails of comets always point away from the sun !

    the gravitational force on a body, which is responsible for its attraction towards the sun, is proportional to its volume and therefore scales with r^3. but the repulsive force from solarwind and radiation pressure is proportional to its surface area and only scales with r^2. therfore large bodys are attracted by the sun while small ones are repulsed. as soon as I find the time I will try to calculate for which size both forces are in equilibrium.

    anyway, even if the dust particle is large enough that the gravitational force dominates, it will be vaporized by solar radiation as soon as it comes close, and the resulting gas atoms will all be repulsed from the sun because of their smallness, as explained above.

    so only bodies that are large enough to reach the sun before they are completely vaporized will add to the suns mass ! perhaps one day I will try to give an estimation for their minimum size, but Im pretty sure that this will be much bigger than "dust" !
  20. May 5, 2008 #19
    Thank you for your answer, I was not near a computer for a while, so I did not answer, but as I started to think about what you said, which seemed very reasonable to me at first many questions came into my mind;
    Does that mean that when a comet finaly gets captured by the sun's gravity, it's tail does not? does it stay floating around? or does it continue in orbit? I am just wondering, what is the exact limit for things that get pushed away from the sun and things that get captured by it. also I am wondering what happen to all the dust when it get pushed away, surely, it cannot escape the sun's gravity. so what doesn't it still contribute to the overall mass(gravity field) of the sun?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook