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Pioneer 10

  1. May 1, 2004 #1
    Did anyone ever find out why pioneer 10 had an anomalous acceleration of 10^ - 8 cm/s/s towards the Sun?
     
  2. jcsd
  3. May 1, 2004 #2
    I once read that MOND (modified newtonian dynamics) was able to explain the anomaly, but MOND seems so a dead theory.

    This recent paper explains the Pioneer anomaly as a result of an "universal adiabatic acceleration of light". It does not seem reasonable to me :wink: :rolleyes:


    http://arxiv.org/abs/gr-qc/0403013
     
    Last edited: May 1, 2004
  4. May 2, 2004 #3

    Nereid

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    AFAIK it's still an open question ... one of the few 'true anomolies' in astronomy/celestial mechanics/etc.

    There are several projects proposed to investigate this 'Pioneer effect', for example
    LISA (note that it's primary objective is to investigate gravitational radiation; detection of the Pioneer effect would be assured under a wide range of likely parameters)
     
  5. May 2, 2004 #4
  6. May 3, 2004 #5

    Phobos

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    Still a mystery as far as I know.
     
  7. May 4, 2004 #6
    As indicated on my page http://www.physicsmyths.org.uk/lightspeed.htm, the apparent anomalous acceleration could be due to a systematic error in relating the travel time of the communication signal to the distance of the spacecraft.
     
  8. May 5, 2004 #7
    Still a mystery as far as I know.

    A guy at Nasa says that they would like to send a probe up dedicated to finding the reason for this anomaly and acceleration anomalies associated with other probes.


    I once read that MOND (modified newtonian dynamics) was able to explain the anomaly, but MOND seems so a dead theory

    MOND isn't dead - there still is no alternative that has explained anomalously high star velocities in galaxies.MOND is hard to test .
     
  9. May 5, 2004 #8
    The questionable point about MOND is that it modifies existing laws of physics without any physical justification (the 1/r^2 dependence of the gravitational force is - like the 1/r^2 dependence of the brightness of a light source - solely a geometrical factor (reflecting the fact that a surface has 2 dimensions) and any deviation from this would need a concrete physical cause (for the case of the light source this could be an absorbing medium, but there is no known physical factor that could account for a corresponding modification of the gravitational force)).
     
    Last edited: May 5, 2004
  10. May 5, 2004 #9
    justification (the 1/r^2 dependence of the gravitational force is - like the 1/r^2 dependence of the brightness of a light source - solely a geometrical factor (reflecting the fact that a surface has 2 dimensions) and any deviation from this would need a concrete physical cause (for the case of the light source this could be an absorbing medium, but there is no known factor that would account for an 'absorption' of the gravitational force)).

    What if gravitons gain energy from the magnetic field of a galaxy as they cross it?
    That would increase the force they exert on a star.
     
  11. May 5, 2004 #10
    What would this have to do with the gravitational force of the sun on spacecraft in the solar system?
     
  12. May 5, 2004 #11
    In George Luis le Sage's theory of pushing gravity gravity particles can travel along way through space and they push masses together - if some gravity particles striking pioneer 10 came from outside the solar system - through a gap in the oort cloud for example - they could pick up a lot of energy - however we'll leave that for theory development!
     
    Last edited: May 5, 2004
  13. May 5, 2004 #12

    Nereid

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    Wouldn't the effect be observable for other space probes too? For example, Voyager 1 and Voyager 2; maybe Ulysses? Even WMAP?? Do you think LISA could test your idea?
     
  14. May 29, 2004 #13
    Dark energy could be causing the anomalous acceleration of pioneer 10.
    The solar system is surrounded by the spherical Oort cloud.If dark energy consists of particles that flow into the galaxy, the Oort cloud would shield
    the solar system from those particles.However a gap in the Oort cloud would allow some dark energy particles to flow into the solar system.
    Dark energy accounts for up to 95 per cent of the mass of the universe
    and the universe has an approximate average mass density of 10 ^ -27 kg/ m^3.So to a good approximation dark energy has a mass density of about
    10 ^ -27 kg/ m^ 3 too.If dark energy particles move at close to the speed of light then 10 ^ -27 kg of them will move through one metre in 10 ^ -8 seconds. The particles will have a total momentum of 10 ^ -27 x 10 ^ 8 = 10 ^ -19.
    The maximum force the particles can exert in 10 ^ -8 seconds on one square metre of pioneer 10 is given by Force = rate of change of momentum / time
    Force = (10 ^ -19 minus 0 ) / 10 ^ - 8 = 10 ^ -11 Newtons.
    Now assuming pioneer 10 has an area facing the direction of travel of the dark energy particles through the Oort cloud and that area is at most 100 square metres (perhaps someone on sci.physics.research knows the exact area!)
    then the total force on pioneer 10 due to dark energy is 10 ^ -11 x 100 Newtons = 10 ^ - 9 Newtons.Since acceleration = force / mass and assuming pioneer 10 has a mass of about 1000 kg ( again, perhaps someone on sci.physics.research can put an exact figure to this), then the acceleration of pioneer 10 towards the sun caused by dark energy particles would be about
    10 ^ - 9 / 1000 = 10 ^ -12 m / s ^2.The figure Nasa gives is 10 ^ -10 m / s ^2.
    If the exact mass and area of pioneer 10 are used, the answer given for the acceleration of pioneer 10 due to dark energy flowing through a gap in the Oort cloud could well be a lot closer.
     
  15. May 29, 2004 #14
    What if the acceleration of Pioneer 10 proves that gravity has certain field of influence before it's effects become nonexistant? That would explain P.10's change in momentum easily. Passing through such a gravitational barrier would be analgous to a micro-particle coasting beyond a magnetic field.

    Just my theoretical two-pence piece.
     
  16. May 30, 2004 #15
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