Pioneer Anomaly: Unravelling Physics' Mysteries

[ohwilleke]

this link may interest you guys!

http://arxiv.org/abs/astro-ph/0503368

Excellent catch. The paper argues that if the density of outer system dust falls off as 1/r and the mass of that dust is somewhat more the current estimates (less than an order of magnitude) that the Pioneer effect would be produced from the gravitational effect of the dust.

It also notes that Nieto, et al are working on a paper on the collision with dust theory which they compare briefly at the end of the paper noting that the collision theory requires a constant dust density compared to evidence the cite that the dust density is not constant but falls off.

 

[tony873004]

The dust causing gravity is my favorite theory so far, but it is not without its flaws. This article states that the entire mass of the dust is 1.97 M_{Earth}.

But there is a problem.

A little background first:

The solar system can be treated like a galaxy in this situation. The Sun orbits the galaxy with the exact same period that it would orbit a single large object at the same distance as the Sun / Galactic center distance, and with a combined mass of all the galaxy's mass interior to the Sun. Therefore, any mass exterior to the Sun's position in the galaxy can be safely ignored.

In a sense, this is like the physics question of how much you'd weigh inside a hollow sphere. Your weight would be 0 no matter where in the sphere you were, and no matter how massive the sphere was. If there was a hollow sphere, with 1 Earth mass and 1 Earth radii, 1 cm thick, (very dense material!, but hypothetical, so why not), and you stood on the surface, you'd find that gravity was 9.8, just like the real Earth. But if there were a hole in the surface, and you jumped through the hole, you'd immediately be weightless.

Dust in the Kuiper Belt would behave the same way. Since its assumed to be distributed uniformly, anything orbiting the Sun interior to this dust belt would not feel the gravitational effect of the dust. But anything exterior to the dust would feel it. It would be the same as if you concentrated all the dust together and added it to the Sun.

So far, this seems to work quite nicely for the Pioneer anomoly. There is no anomoly if you are interior to the belt in the same plane as the belt.

But now the problem:

How much dust would it take to cause an additional acceleration of 8.7*10^{-8} cm/s^2

a = \frac{GM}{r^2}

therefore

M=\frac{ar^2}{G}

8.7*10^{-8}cm/s^2 = 8.7*10^{-10} m/s^2

G=6.673*10^{-11}Nm^2/kg^2

r = 1*10^{13}m (roughly the current Pioneer / Sun distance)

M = \frac{8.7*10^{-10}*(10^{13})^2} { 6.673*10^{-11}}

M=1.3*10^{27}kg

\frac{1.3*10^{27}kg}{5.98*10^24 kg/M_{Earth}} = 218.12 M_{Earth}

which is much higher than the article's value of 1.97 M_{Earth}

 

[Chronos]

I'm a bit short of time or I would do the math myself, but I believe even the 1.97M figure would be enough to influence the outer planets orbits. 218M unquestionably would.

 

[ohwilleke]

I'm a bit short of time or I would do the math myself, but I believe even the 1.97M figure would be enough to influence the outer planets orbits. 218M unquestionably would.

The article argues that there is a modest effect on outer planet orbits, and implies that current predictions are based on the wrong "initial conditions" so to speak.

 

[tony873004]

I'm a bit short of time or I would do the math myself, but I believe even the 1.97M figure would be enough to influence the outer planets orbits. 218M unquestionably would.

Not if its all exterior to the outer planets, and evenly distributed. Then the outer planets are like a person in a hollow sphere, unable to feel the effects of the sphere's gravity.

Jupiter orbits exterior to Mars, but tugs Mars eccentricity into and out of round periodically. (Jupiter does this to Earth too but to a much lesser degree). But if Jupiter exploded and formed a belt of dust with 1 jovian mass, evenly distributed over Jupiter's orbit, Mars would no longer know this mass existed.

Observations with IR suggest that 218 Earth masses of dust in the Kuiper belt is unrealistically high.

The article argues that there is a modest effect on outer planet orbits, and implies that current predictions are based on the wrong "initial conditions" so to speak.

The article claims that the dust belt begins just past the orbit of Uranus. It talks about an effect on Neptune, but not the planets interior to the dust belt.

 

[Billy T]

I did not know of the "Pioneer Anomaly" when I wrote Dark Visitor, but did know that in the early part of the last century that Neptune's orbit was disturbed - Based on his analysis of this disturbance, Percival Lowell founded the observatory near Flagstaff AZ and financed the discovery of Pluto, but Pluto needed to be many times the mass of the Earth to have produced the perturbations. We now know that Pluto is smaller than the moon, so the perturbation, if real, was something else. I used these "Pluto facts" plus the fact that when the universe was about 25 times smaller, the first stars were forming, were larger, aged rapidly and several generations of them left pairs of gravitationally bound black holes behind, long before our sun was born.

If the first member of a BH pair, approaching from the north polar region, passed not too far from our solar system, cutting thru the plain of the ecliptic in 1928, it could have been the cause of Neptune's perturbation and tilted Pluto's orbit plane. The second member of the pair could be approaching about now, but still not detected as black holes do not reflect sunlight.

The hero of my story (Astronomer Jack) has been carefully measuring Pluto and Neptune for several years and from their unexplained residual perturbations computed a rough trajectory for the now approaching second member of the 1928/2008 pair.

In fact there are several reasons why Jack's small (2.2 solar mass) BH now 130 AU from the sun might be more directly noticed. The Pioneer acceleration anomaly would be nearly two orders of magnitude greater, but you might want to think about the other reasons.

Dark Visitor was written as a recruiting tool for the hard sciences. I am a retired professor and very concerned that the western world is now in the process of losing scientific leadership to hard working, studious Asians, as it has already lost technological leadership and many good jobs. I don't want my grandchildren to have only "non-exportable" jobs like cutting some one's hair or selling fast food, etc.

If you share my concern, please visit www.DarkVisitor.com where you will learn how to read entire book for free, get a list of all the science hidden in it, sample text, etc. The target reader is not currently interested in science -that is why it is a scary, but possible real, story of a coming cosmic disaster that change Earth's orbit enough (more elliptic by about 10%) to initiate a new ice age beginning in 2008.

 

[notknowing]

One question is why is this anomalous acceleration detected on distant spacecraft but not on other orbiting bodies?
It may be explained by a clock drift between atomic clock time and ephemeris clock time, the acceleration being approximately the Hubble acceleration, http://arxiv.org/abs/gr-qc/0403013
a_p ~ cH.

Such a clock drift is predicted by SCC.

Garth

Thanks Garth for this interesting reference. The paper is rather convincing and is based on established principles. There is also an interesting analogy with Puthoff's theory (discussed in earlier treads) on the influence of gravity on the electrical permittivity and magnetic permeability of the vacuum (same dependence)- see equation 12.
Now, if this explanation is, even partly, correct, it would probably mean that a number of cosmological "observations" such as redshifts, distances to galaxies, estimates of dark matter (which I think does not exist) and dark energy, etc are erroneous and need to be corrected for this effect. Would you agree on this ?

 

[Garth]

Thanks Garth for this interesting reference. The paper is rather convincing and is based on established principles. There is also an interesting analogy with Puthoff's theory (discussed in earlier treads) on the influence of gravity on the electrical permittivity and magnetic permeability of the vacuum (same dependence)- see equation 12.
Now, if this explanation is, even partly, correct, it would probably mean that a number of cosmological "observations" such as redshifts, distances to galaxies, estimates of dark matter (which I think does not exist) and dark energy, etc are erroneous and need to be corrected for this effect. Would you agree on this ?

Let me answer cautiously.

Astrophysics is the application of laboratory or 'local' physics to the universe 'out there'. Cosmology is the extension of that discipline to the largest possible scales.

The overall theory that describes the cosmological environment, in which the locally understood and tested theories of atomic processes and nucleosynthesis etc. are set, is General Relativity.

That theory has been well tested in local solar system experiements and on the largest scales produces the standard \LambdaCDM model. That model fits the multitude of observations of Hubble Red Shift, BBN, CMB anisotropies, distant Type Ia supernovae, large scale structure etc. very well.

However it does so by introducing a series of 'entities', Inflation, exotic non-baryonic DM and DE that have not been identified in local physical experiments.

When we discover the Higgs Boson/Inflaton, the DM particle and identify DE in the laboratory (LHC?), measure their properties and show that those observed properties match the cosmological observations then and only then will we know what we are really talking about.

In the meantime questions remain about the development of a Quantum Gravity theory, and pertinent to that, whether GR really does describe local gravitational fields accurately. The Pioneer Anomaly (its Doppler drift is almost equal to the Hubble Constant) may indicate that it does not.

Remember the discovery of Pluto because of a residual anomaly in Uranus' orbit after Neptune had been taken into account? Pluto is too small (by a factor of 2 OOM) to have been the Planet X they were looking for. So unexplained residuals may still exist in the orbits of the outer planets as well!

I think we should have open minds while these questions remain, other theories that are alternatives to, or modifications of, GR have a mountain to climb, however they should not be discarded because of that. Alternative theories to GR (such as http://en.wikipedia.org/wiki/Self_creation_cosmology will shed further light on the issue in April!

Garth

 

[henryco]

Hi,

Another simple way to understand the pioneer anomaly:

Suppose that at a distance between us and Pioneer the cosmological scale factor in conformal time units switches (a discrete jump) from a(t) to 1/a(t).
As a consequence there will be a 1/a^2(t) deceleration of Pioneer clock (i.e frequency of the radio wave we receive from it) relative to our Earth clock (in a theory where the background effects are not suppressed by the local gravitational field as in GR)..
As a straightforward result: (df/dt)/f=-2H0 as you can check and as is observed. This is also, as in SCC, a deceleration of clock explanation of the anomaly but in quite different way: it needs at least to spatial areas with different background evolutions.
The dark gravity theory (gr-qc/0610079) equations admit both a(t) and 1/a(t) solutions and nature has to choose between them at some places in a discrete way in order to restore a better discrete symmetry involved in the fundations of the theory which i cannot devellop here.
As you can see in the paper by ANderson , the effect appeared quite abruptly in 1983 around 12.5 A.U
Within the error bars i couldn't hope a better signature : Pioneer just crossed the background discontinuity in 1983 at 12.5 A.U
The foreseen consequences for the near future are here: www.darksideofgravity.com/armagfr.htm[/URL]

regards,

F Henry-Couannier

 

[Chronos]

Keep in mind the lunar laser ranging project has been collecting data for nearly 40 years. It should be interesting to compare GPB results with those of that study.

 

[henryco]

Keep in mind the lunar laser ranging project has been collecting data for nearly 40 years. It should be interesting to compare GPB results with those of that study.

Sure! as far as i know, nothing anomalous was found (and the last article by Turyshev confirms this) in LLR data, but i was also told that this analysis is extremely complicated...

Anyway, exporting their data in the sun reference frame it appears that they can even see with great precision a frame-dragging effect due to the Earth motion about the sun in this frame. But the LLR data were taken in the Earth rest-frame so, their frame dragging signal is nothing but the effect they themselves injected in their data by lorentz transporting them in the sun rest-frame (see this month article by Turyshev)!

If, and this is what you can read in red in the latest version of my article gr-qc/0610079, if the transformation group is the Gallile one instead of the Lorentz one, you are still OK with all test of PPN alpha parameters which only test boost invariance and not Lorentz invariance as is always claimed.
But under such transformation, g_munu behaves differently. So LLR data analysers may be should not perform a Lorentz transformation.
In GP-B because you test frame-dragging in a frame where the Earth is rotating, you can really test what is the correct transformation group under boosts.

F H-C

 

[henryco]

Keep in mind the lunar laser ranging project has been collecting data for nearly 40 years. It should be interesting to compare GPB results with those of that study.

Hi,

PLease have a look at gr-qc/0702028 the latest paper by Turyshev, Nordtvedt and co regarding gravitomagnetism.
It says something incredible! It says that the frame-dragging is seen in the frame of the observer (earth frame) where there should be nothing at all since in this frame the speed of the Earth vanishes...but they keep using there (badly incorrect) the gravitomagnetic field formula of the sun rest frame. Crazy isn't it?

Best regards

Fred

 

[Chronos]

Same paper I had in mind, Fred. I didn't notice any problems with their approach, but will read again. Interesting stuff for sure.
http://arxiv.org/abs/gr-qc/0702028
The Gravitomagnetic Influence on Gyroscopes and on the Lunar Orbit
Authors: T. W. Murphy Jr., K. Nordtvedt, S. G. Turyshev

 

[henryco]

In a previous post i said:

...they keep using there (badly incorrect) the gravitomagnetic field formula of the sun rest frame. Crazy isn't it?

Fred

At least, if they are actually working in the sun rest frame, should they study small acceleration perturbations making the trajectory deviating not from a circle as they did , but from a Lorentz transformed circle (moon trajectory should look like a rugby ball after Lorentz transport from a comoving frame). May be they applied this correction elsewhere but it should be mentionned in the paper formula for these to be correct, not elsewhere, i believe...tell me if I'm wrong.

best regards

Fred H-C

 

[Garth]

Garth: I think you mean H₀, don't you? If so, then the MOND figure would be either a coincidence, or easily testable (what value best fits the rotation curves of very distant spirals?).

A paper by Bekenstein & Sagi in today's physics ArXiv asks the same question as in this old post of Nereid's: Do Newton's G and Milgrom's a₀ vary with cosmological epoch ?.

In the scalar tensor gravitational theories Newton's constant G_N evolves in the expanding universe. Likewise, it has been speculated that the acceleration scale a₀ in Milgrom's modified Newtonian dynamics (MOND) is tied to the scale of the cosmos, and must thus evolve. With the advent of relativistic implementations of the modified dynamics, one can address the issue of variability of the two gravitational ''constants'' with some confidence. Using TeVeS, the Tensor-Vector-Scalar gravitational theory, as an implementation of MOND, we calculate the dependence of G_N and a₀ on the TeVeS parameters and the coeval cosmological value of its scalar field, \phi_c. We find that G_N, when expressed in atomic units, is strictly nonevolving, a result fully consistent with recent empirical limits on the variation of G_N. By contrast, we find that a₀ depends on \phi_c and may thus vary with cosmological epoch. However, for the brand of TeVeS which seems most promising, a₀ variation occurs on a timescale much longer than Hubble's, and should be imperceptible back to redshift unity or even beyond it. This is consistent with emergent data on the rotation curves of disk galaxies at significants redshifts.

Garth

 

[HenriPoincare]

http://www.space.com/scienceastronomy/080229- spacecraft -anomaly.html