After a long hiatus, the Pioneer Anomaly finally resurfaces in the news circuit with an article from Space.com.

"Researchers want to determine whether heat from Pioneer probes’ electronics or two nuclear power sources—known as radioisotope thermal generators (RTGs)—could be emitting infrared photons that then smack into the spacecraft’s dish-like main antenna, causing a recoil effect that Turyshev likened to sunlight striking a solar sail.

Analysis and modeling of how the Pioneer 10 spacecraft emits heat from various sources, including its RTG, found that they account for between 55 percent and 75 percent of Pioneer Anomaly, said Gary Kinsella, a group supervisor for spacecraft thermal engineering and flight operations at JPL. "

http://space.com/scienceastronomy/070327_s...ioneeranom.html

I can see a problem right off the top with this scenario: The thermal output from the RTGs diminished considerably during the ten-plus years that the probes were monitored - but the measured acceleration anomaly during the same period was constant. (In order for the two effects to be related, you would have to explain why the depleting RTGs would result in constant acceleration.)

Most of the power loss is due to the degradation of the electronics - the actual decline in the output of the plutonium is much less pronounced.

The problem with the most recent space.com article is that it really lacked details, and their “preliminary results” had huge error bars. I’m going to wait for more concrete conclusions to come out in publication.

In the mean time, a very nice account of the progress and data recovery just showed up at the Planetary Society. (Thanks, Emily!) It’s a very nice read on the challenges of handling and eventually analyzing data generated over very long time periods. When the “experiment” started, computer technology was still very young.

Slava Turyshev gives a few details on the thermal modeling, but stops short of the claims in the space.com article.

"Our thermal modeling of the Pioneer vehicles is progressing very well. We finished the development of the geometric mathematical models of the spacecraft that include geometry and properties of most of the important spacecraft components and surfaces. We are now working on the thermo-dynamical model of the vehicles. At this stage, we have a very good understanding of heat re-distribution within the craft and soon will be ready to compute the heat flow to the outside of the craft. Soon, we will be able to tell whether or not heat contributes to the formation of the anomaly."

http://planetary.org/programs/projects/pio...e_20070328.html

You're welcome, but Slava wrote it; all I did was post it. I'll be happy to forward your thanks on to him.

--Emily

Not to drift into tin-hat-land at all, but I keep wondering if our imperfect understanding of the true value of the gravitational constant might be the ultimate culprit here. Experimental results for G are inevitably wildly different from one another even at the third digit past the decimal point, which implies uniquely large uncertainty for a physical constant (insert various curses for the fact that the Earth is not a uniform sphere of homogeneous composition here! ) Can't understand why the particularly large error bars for this constant might not encompass the domain of the anomaly.

Try G=6.671281904 exp -11. If it works, I'll explain why via private correspondence in order to ensure that UMSF does not stray outside forum guidelines during the discussion (a distasteful possibility given the crackpot aura around gravitation); if not, forget I said anything, and thanks for the reality check. That's a firm heuristic, period.

The half-life of the Pu 238 is 87 years. Since 1977 their thermal output has dropped ~21%.

Some of the reduction in electrical power generation is also due to the changing temperature differential, which decreases the efficiency of the thermal energy. Perhaps this is what you meant by "degradation of the electronics". However, this does not play into the net thrust of the thermal radiation.

IIRC, while our knowledge of the value of G is imperfect, our knowledge of the gravitational constant of the sun is very precise. So our value for G could be in error on the low side, but then our measure of the mass of the Sun would be in error on the high side, or vice versa.

Radiation damage to the thermoelectric diodes causes a large fraction of the total power decline in RTG's. It's minor for a normal mission, but nukes your power margins (don't pardon the pun), on a decades long mission.

Exotic cause of 'Pioneer anomaly' in doubt
08:00 22 June 2007
NewScientist.com news service
David Shig

The big difference between the Pioneer spacecraft and any solar planet is that the planet is in a bound orbit, while the Pioneers are in an unbound trajectory.

What if the 'Pioneer Anomaly' is dependant on radial velocity from the Sun, being zero if the object's radial velocity is zero, increasing in a linear fashion towards the Sun for objects moving outwards, and increasing in a linear fashion away from the Sun for objects moving inwards.

A planet in a bound orbit would by definition have equal amounts of inward and outward movement, so over the whole orbit the 'Pioneer Effect' would be canceled out. The amount of displacement over the orbit would be impossible to detect, due to its small magnitude (because of the small radial velocities), working over short timespans (half an orbital period).

The Pioneers, by contrast, have much higher outward radial velocities, causing the anomalous effect to be larger, unbound trajectories, allowing the magnitude of the effect to build up over time instead of being canceled out, and were tracked by radio, allowing for much smaller effects to be noticed than is the case with the planets, whose positions must be optically observed. If the planets deviate by a few km at most, then return to the calculated positions every orbit, the deviation would go un-noticed. (Radar may change this in the future, at least for the nearby planets -- but are they looking for the effect?)

edit -- In addition, the 'Pioneer effect' would simply slightly decrease the eccentricity of a planetary orbit, pushing the perihelion out a few km, and the aphelion in a few km. It might have been already detected, but misinterpreted as a slightly lower 'true' eccentricity for that planet than the actual value.

Bill

If this were true a planet would gain less potential energy on the outward path than it lost on the inward one, making a net energy gain on every orbit. Over a long enough period of time I think this would produce fairly spectacular results.

Interesting comment within the article:
http://space.newscientist.com/article/dn12...y-in-doubt.html


Tangen did not consider the cases which would involve violation of the equivalence principle, so Tangen has only addressed a small subset of possible scenarios, establishing modest constraints.

If the anomaly is a function of the radial velocity relative to the sun as Mongo supposed; if I remember right, Pioneer 11's last gravitational assist swung it initially on a vector that passed closer to sun than the Saturn orbit. The extended data set retrieved by the Planetary Society includes this period, so any radial dependance may be apparent in this extended data set.

I am not sure I follow here. A planet on the 'outward' half of its orbit would be pulled slightly inward, as if the Sun's gravitational pull were slightly stronger, and on the 'inward' half of its orbit would be pushed slightly outward, as if the Sun's gravitational pull were slightly weaker. The sum of the inward and outward phases would be the same as if the Sun's gravitational pull were constant at its true value, provided that the effect is linear with radial velocity -- as can be proven using elementary geometrical arguments.

There is one possible observable effect: because of the slight difference in the Sun's effective gravitational pull between bodies moving toward or away from the Sun, the 'outward' phase of the planet's orbit would last slightly less long than the 'inward' phase (in order for the energy transfer to balance between the two phases, and also because the planet would 'decelerate' moving outwards more quickly than it would 'accelerate' moving inwards). This difference would be very small -- perhaps a few minutes? -- but might possibly result in a detectable deviation from a perfectly elliptical orbit. Although the deviation would be extremely small.

Bill

Energy is the integral of force over distance, so if the force is greater going one way than the other then energy is not conserved around a closed orbit.

I am not sure that this applies here, though. Force is defined as mass times acceleration, and the Pioneer effect could be viewed as if the inertial mass of the planet were slightly lower on the outbound phase of its orbit than on the inbound phase. (Hence the increased apparent gravitational pull of the Sun -- the acceleration would be determined by the Sun's gravitational acceleration at that distance times the ratio between the planet's standard mass and its inertial mass. If the inertial mass were half the standard mass, the planet would decelerate at twice the 'expected' rate) The slightly higher deceleration of the planet, times the slightly smaller inertial mass, would result in the same force due to gravity being applied to the planet as there would be under standard physics.

Bill

Are you saying it's inertia would be different in the radial direction from what it would be at 90 degrees to that direction? I'm not at all happy with that idea. Mass is a scalar property - or are you saying not in this case? I'm off home now but will continue to mull it over . .

Well... (thinking about it) ...I would assume that the gravitational force exerted on the orbiting body always remains the same as it would be under 'standard' physics, for the reason that you had mentioned. But in addition to the the 'standard' effect that varies with radial distance, approaching zero as radial distance R approaches infinity, and inversely proportional to the square of the radial distance:

1) f1 = G1*m1*m2*R^-2

Where f1 is the 'actual' gravitational force exerted on the body, and G1 is Newton's gravitational constant. A second-order effect of that force on the object's trajectory would vary with radial velocity (distance over time), reaching zero as radial velocity reaches zero, and linearly proportional to (the negative of) the radial velocity:

2) f2 = -Ga*m1*m2*v

Where f2 is the pseudo-force exerted on the body, v is the radial velocity and Ga is a second gravitational constant, possibly equal to G1. f2 would be much smaller than f1 at non-relativistic velocities, reaching zero as v reaches zero, but I would not be surprised if it approached f1 as v approaches c, so that Ga equals G1. Combining the two:

3) f1+f2 = (G1*m1*m2*R^-2) - (Ga*m1*m2*v)

The 'Pioneer effect' can be viewed as a modification of the well-known Newtonian force f1:

4) f2 = f1*R^2*v*G2 where G2 = Ga/G1

Resulting in:

5) f1+f2 = (G1*m1*m2*R^-2)*(1 - R^2*v)

if G1 = Ga, as I think it could be.

So, again assuming that Ga = G1, the change in the second-order 'force' must be proportional to v, with the inertial mass equal to the first object's rest mass times (1-v) in natural units (c = 1). This is of course the opposite effect as that described in special relativity, in that with special relativity, the inertial mass equals the rest mass times the square root of (one over (1-v))

Bill

Have you worked out what that would do to the perihelion of Mercury?

I was looking at a paper discussing modified-inerta MOND theories, and came across the following (MI = Modified Inertia, MG = Modified Gravity):

http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0510/0510117v1.pdf

MOND as Modified Inertia



If the Anderson analysis of the anomaly is correct, then the 'Pioneer effect' will never be detected in the orbits of the planets. A radio transponder (or possibly a laser reflector) placed on an unbound Solar-escape trajectory would be needed to study it.

Bill

The Deen report provides a different way to present the telemetry blueshift.

Although the Pioneer 10/11 anomaly is presented as a "sunward acceleration", the actual data is the continuing blueshift of the telemetry signal. A researcher prepared a report that proposed a mechanism for the blueshift, it being caused by a changing "index of refraction" in what amounts to a segmented cosmic lens about the sun.

http://www.vip.ocsnet.net/~ancient/Deen-20...-10-Anomaly.doc

It should be noted that the author inverted the algorithm normally used to calculate the index of refraction, n, see Para. 4 of the report. He held v constant (inside 20 AU) and allowed c to change as the spacecraft went outbound, thus resulting in an increasing value for n. The increasing n is directly proportional to the increasing blueshift with distance.

Para. 1 of the report states the effect quite directly, "A photon emitted by a spacecraft outside the entire onion would experience successive speed reductions as it crossed successive shell boundaries moving inwards towards the Sun."

I hold a slightly different view than Deen, as I doubt the volume surrounding the Sun is layered, it has a constantly changing index of refraction, starting at the Sun's surface and extending outward to the limit of the heliosphere (or beyond). It is easier to visually present the constantly changing density as a series of layers, otherwise the density at a given point in space will be a function of the inverse square of the distance.

The detected blueshifted telemetry frequency is a reflection of the average value of the velocity of the telemetry signal as received at earth from the spacecraft at any given point in time.

We know the index of refraction for EM waves has a value of 1 as measured in a vacuum on the earth's surface. (diffraction index)^2 = (relative permittivity)

An increasing blueshift, due to a change in the index of refraction implies that the speed of light is increasing with increasing distance from the sun. We should expect this to a very small degree, because the solar wind is thinning (the absolute vacuum of space is becoming more absolute). I don't recall that the calculations used by Anderson & Co. including any terms for the decreasing density of the helosphere.

There is a problem with this interpretation: The rate of blueshifting should decrease with increasing distance; but the anomally, on the scale that it has been detected, is quite linear. Still thinking out loud, this does not rule out a refractive solution if the density of the solar wind is roughly constant in the same region. Its too bad we do not have a pioneer-like probe well beyond the helopause. It would be easy to rule out / rule in such a solution simply by looking at the redshift of the sun.

The rate of blueshifting is decreasing with distance. Each segment, Figure 4 or Figure 5, represents the same acceleration magnitude but the time required to achieve the same magnitude, and same blueshift, of the previous period is increasing. Under Figure 4 of the article, Deen states,

I haven't found any mention in any of the Anderson&Co reports that the density of "something" is changing outbound from the sun.

I thought the Deen report was an interesting way to present the acceleration (blueshift) data. It makes it easier to visualize the persistence of the shift.

In order to see the progression of the spherical shells illustrated in Deen's report, I replicated his nine pair of data points in a spreadsheet and extended the shells inward and outward. Deen's spherical shells follow the standard formula for such volumes.

What I really need is a spreadsheet algorithm that uses the primary anomaly variable, the value of the blueshift. I would like to see is how close the blueshift converges to zero at the Earth 1 AU distance.

Is there a report that gives the actual blueshift value at 20 AU?

I found a neat site that allows one to put in a set of values and it returns the regression results.

http://people.hofstra.edu/stefan_waner/Rea...sionframes.html

My first set used R in and the refraction index and the second set R out and the refraction index. I didn't get a good fit with any regression process for R in, but had a near perfect fit with R out.

The best fit for the outer R gave an r = 1 the equation being y = ax^b with y =.000124956x^2

I suspect the way Deen extracted his data influenced the R in vs R out data sets, the actual refraction index being tied to the R out value.

This indicates that whatever is causing electromagnetic waves to change their velocity has a near perfect fit to the square of the distance.

There were several structural problems with the Deen report, three equations did not display and the references were missing. The author has made his report available in pdf form and it includes all of the material.

http://www.glendeen.com/npa2007/Deen_2007_..._10_Anomaly.pdf

The primary reference [1] is available at arxiv.org and it is the 2005 revision. It is a 1.5 mb file.

http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064v5.pdf

I just noticed the team working on data recovery put out a new update:
"Pioneer Anomaly: Evaluating Newly Recovered Data".
They still aren't quite to the point of having a calibrated unified dataset -- by the end of the year, they say.
It does sound like their heat modeling project is going pretty well. I'm really hopeful that they will be able
to conclusively answer whether or not thermal forces can explain the anomaly.

Catching up on reading ESO Messenger reports I came across an article in the June 07 edition (#128) in which Newton's law was tested in the low acceleration regime (outer regions-) of globular clusters. The rather astounding conclusion was that globular clusters behave like galaxies in that the velocity pattern in these outer regions flattens off in exactly the same pattern as measured for galaxies.

For this behaviour around galaxies it is widely assumed that large quantities of dark matter (hidden in the galaxies) are responsible. But for globular clusters this explanation is apparently not valid at all. Ergo, it seems that one of the main reasons for "inventing" dark matter in large scale gravity puzzles is no longer valid and that alternatives such as MOND gain a lot of credibility. Especially since it is "unpalatable" as the authors decribe it to assume that dark matter also is a pervasive factor in globular clusters. If someone could explain that to me that would be highly appreciated, but I take the word of the authors until advised otherwise.

A modified Newton law would also go a long way in describing the Pioneer anomaly I believe. This thread will probably remain open for quite some time to come. (Pls support Doug with his new server project )

To top it all off, in the Febr08 number of Ciel et Espace there is an article describing a new competitor for MOND, called MOG for Modified Gravity theory. The Pioneer anomaly, which started as a fairly low-key issue, seems on the up again now that Newtons law is shaking, at least in the low acceleration regime. What will be next??

Instead of citing the names of the authors, apologies if I should have done so, here is the link to Messenger #128. Read for yourself!
http://www.eso.org/sci/publications/messen...enger-no128.pdf

Using globular clusters to test gravity in the weak accelleration regime

New work on thermal modeling the affect of IR scattering off of the back of the HGA purports to explain the entirety of the anomaly:
http://www.technologyreview.com/blog/arxiv/26589/

And NASA takes another look:
http://www.technologyreview.com/blog/arxiv/27012/

(Links to referenced papers in both this and the last article.)

From Support for temporally varying behavior of the Pioneer anomaly from the extended Pioneer 10 and 11 Doppler data sets

"The main question is whether or not a statistically significant anomalous acceleration signal still remains in the residuals after the thermal recoil force has been properly accounted for. Results of this meticulous study will be published soon."



Unfortunately, the paper does not appear to give error bars.

Assuming that the error bars are small enough that the above diagram (especially the "Stochastic Acceleration" portion) is reasonably accurate, it looks to me like the acceleration curve flattens out to an asymptotic value of about 7 x 10^-10 ms^-2.

The most obvious cause, in my opinion, would be an exponential decaying acceleration with a half-life of about 3-4 years (declining due to radioactive decay in the RTG?) plus a steady acceleration of unknown origin of about 7 x 10^-10 ms^-2.

Of course I am no expert.

The name of the game has always been to grow the thermal differentiation to the point that the error bars overlap the known radioactive decay profile; providing a plausible solution.

Looks like the mystery has been solved...

Pioneer Anomaly Solved: The Planetary Society

I'd also heard that the ESA was considering a mission to probe the effect, but I've not been able to find out much about it.

see for example
A Mission to Explore the Pioneer Anomaly, OSS (Outer Solar System): A fundamental and planetary physics mission to Neptune, Triton and the Kuiper Belt, Odyssey 2 : A mission toward Neptune and Triton to test General Relativity

LOL, sounds like UMSFs crack Ice Hunters might get a new gig.

Let's go get 'em a big un !!

Not much reason to send one entire new mission or studies IMO.

The case might be quite closed and filed after JPL have had another look at the matter.

The paper by Francisco, Bertolami and Páramos is found here:
http://arxiv.org/pdf/1103.5222v2