What Caused the Pioneer Anomaly?

[mathman]

http://spectrum.ieee.org/aerospace/...echalert&utm_medium=email&utm_campaign=120612

I believe this settles it.

 

[berkeman]

From near the end of the long article:

We also calculated the thermal recoil force on the spacecraft using just the Doppler data, by computing the force needed to match the probes’ trajectories. When we compared this independent estimate with the one derived from the spacecraft model, we found that the two values matched within 20 percent. Once uncertainties are taken into account, there is no statistically significant difference. Three decades after its discovery, we can now say there is no exotic cause for the Pioneer anomaly: The puzzling deceleration was produced by the asymmetric radiation of waste heat created onboard the spacecraft .

 

[Drakkith]

Excellent!

 

[Old Smuggler]

No mention was made of the criticism from Anderson & Morris; see
J.D. Anderson and J.R. Morris, PRD 85, 0840817 (2012). A & M plotted
the alleged "decay" of the anomaly as a function of the radius R from the sun
and found that it goes almost exactly as 1/R^2. This behaviour makes it likely
that the alleged decay is only an artefact due to a mismodelling of the solar
radiation pressure on the spacecraft .

With the "decay" of the anomaly removed, the claim that the thermal model agrees
with the Doppler data to within 20% would hardly be valid. So I think that before
they have explicitly refuted the criticism from Anderson & Morris, it would be
unwise to draw any firm conclusions regarding the status of the anomaly.

 

[Enthalpy]

I'm extremely skeptical about this "explanation" since it was one of the first dismissed by the same authors in their original paper.

Among the many dozens of explanations refuted then, thermal recoil was one of the simplest and the effect has been checked by so many people.

 

[Drakkith]

I'm extremely skeptical about this "explanation" since it was one of the first dismissed by the same authors in their original paper.

Among the many dozens of explanations refuted then, thermal recoil was one of the simplest and the effect has been checked by so many people.

But not to the extent that this team did.

 

[Maui2001]

According to the information contained in the following paper, asymmetric heat dissipation should only account for about half of the anomalous acceleration at most:

http://link.springer.com/article/10.1007/s10509-011-0789-4

 

[Drakkith]

According to the information contained in the following paper, asymmetric heat dissipation should only account for about half of the anomalous acceleration at most:

http://link.springer.com/article/10.1007/s10509-011-0789-4

That article proposes a second gravitational constant.
I'm going to stick with the heat dissipation theory for now. I believe it's far more likely than modifying gravity.

 

[Maui2001]

The heat dissipation model was applied to the Pioneer 10 data, but not to the Pioneer 11 data set. Pioneer 11 exhibits a distinct variation with respect to heliocentric distance during the first 5 years of its mission (the onset of the Pioneer anomaly). The heat emission model proposed by Turyshev et. al. in their June 2012 paper is unable to account for it. They address this issue at the end of their paper by stating that “In closing, we must briefly mention additional avenues that may be explored in future studies. First, the case of Pioneer 11 was not analyzed at the same level of detail, albeit we note that spot analysis revealed no surprises for this spacecraft . Second, the question of the anomalous spin-down of both spacecraft remains unaddressed, even though it is plausible that the spin-down is due to heat that is reflected asymmetrically off instrument sunshades. Third, Fig. 2 is strongly suggestive that the previously reported “onset” of the Pioneer anomaly may in fact be a simple result of mismodeling of the solar thermal contribution; this question may be resolved with further analysis of early trajectory data.”

In other words, since the data for Pioneer anomaly doesn’t fit their model, they claim that the data itself is wrong, not the model. Sounds a bit backwards, don’t you think?

 

[Drakkith]

In other words, since the data for Pioneer anomaly doesn’t fit their model, they claim that the data itself is wrong, not the model. Sounds a bit backwards, don’t you think?

Where did they claim the data was wrong? All I see is that they didn't analyze the data for Pioneer 11 in as much detail as they did for 10, and that they believe a previous model is incorrect.

 

[Maui2001]

"Third, Fig. 2 is strongly suggestive that the previously reported “onset” of the Pioneer anomaly may in fact be a simple result of mismodeling of the solar thermal contribution; this question may be resolved with further analysis of early trajectory data.”

Their model predicts that the heat dissipation should be at its greatest early in the mission, yet this is precisely where the anomalous acceleration is smallest. They attempt to reconcile this difference by stating that "mismodeling of the solar thermal contribution" is at fault, since the data disagrees with the predictions of their model.

 

[Drakkith]

And? So what? I see no problems with mentioning a possible reason that their model doesn't work. It appears they have at least some reason to believe mismodeling may have occurred.

 

[Maui2001]

Based on what exactly?