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Dark Matter in the solar system.

  1. Dec 8, 2008 #1


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    Here's a question for the astrophysicists here:

    Is the commonly predicted amount of Dark Matter and its distribution in our solar system expected to be such that it has an appreciable effect on the orbital speeds of any of the bodies in our solar system?
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  3. Dec 8, 2008 #2


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    I believe not, gabba. It is too diffuse and unreactive to have an appreciable effect on orbits.
    I know of a research paper by Magueijo that proposed a very delicate experiment using a spacecraft (LISA http://en.wikipedia.org/wiki/Laser_Interferometer_Space_Antenna) primarily intended to pick up gravitational waves. He proposed the space instrument, LISA or the earlier LISA pathfinder, be put to an alternative purpose--detecting dark matter.

    Maybe other people know of other proposed experiments to detect dark matter within the solar system by its gravitational effects. But it would not have a measurable effect on orbits.

    I expect you know of other ways of detecting dark matter: either
    1. by its decay into ordinary matter (initial results still require confirmation)
    2. dark matter outside the solar system seen by weak gravitational lensing (DM in the foreground distorts images of galaxies in the background)
    Last edited: Dec 8, 2008
  4. Dec 8, 2008 #3

    “Planetary orbits, if there were enough dark matter present, would have their perihelia precess faster than if there were no dark matter. The amount of dark matter allowed from these observations is considerably greater than the amount I predict. The errors on the measurements of perihelion precession are in units of hundredths of an arc second per century…Even if you assume the dark matter is at rest with respect to the galaxy that the Solar System moves through (which is the extreme example), the Sun is of order 10^30 kg; capturing a 10^20 kg clump of dark matter will slow you down by about 20 microns/second over the lifetime of the Solar System. So that would be small." – Ethan Siegel in an email interview.”

    Yes, it seems that it is pretty negligible.
    (Not that I am an astrophysicist)
  5. Dec 8, 2008 #4
    You mean that dark matter is reactive when needed for the explanation of abnormal phenomena (galaxy rotational curve, micr-lensing) and un-reactive when un-needed for solar movement (Newton law of gravity is enough)?
  6. Dec 8, 2008 #5


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    Thanks Marcus and Arch!

    I was recently wondering how it is that dark matter has such a significant effect on the orbital speeds of the stars in our galaxy, but no noticeable effect on the orbital speeds of planets in our solar system (as far as I was aware of anyway).

    Xu and Siegel's paper (the one quoted in the link Arch posted) seems to be very much along the lines of the explanation I was looking for. Do either of you know of any other papers that deal with this subject?
  7. Dec 9, 2008 #6
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