Data, Dogma, and Truth Too Detailed to Matter (most of the time)


There are so many lessons in this story it is hard to know where to start. First, don't throw away data. Second, scientists do question their own dogma and in fact get rather excited about it. Third, Click and Clack (Car Talk) glossed their answer to a question the other day (sort of) ... it turns out that running the heater in your convertible does affect the entire planet. A little.

Pioneer 10 and 11 left the the main part of our solar system a long time ago. As they headed on their journey to other worlds, they seemed to slow down in comparison to predictions of their actual rate of movement. This slowing has become known as the Pioneer Anomaly.

One of the most intriguing mysteries in physics is the "Pioneer anomaly," the slowing down of two spacecraft by an unknown force. NASA launched Pioneer 10 and 11 in 1972 and 1973, respectively, and the craft returned stunning images of Jupiter and Saturn. But as both spacecraft continued their voyages at speeds of roughly 27,000 miles per hour, astronomer John Anderson of the Jet Propulsion Laboratory in Pasadena, Calif., noticed anomalies in telemetry data dating from as far back as 1980. With continued analysis, researchers determined that the spacecraft had been slowing down at a constant rate: each year they fell 8,000 miles short of their calculated positions. The strange behavior sparked several theories, but the lack of data made culling the ideas difficult. Now a proposal to analyze telemetry from the early years could literally point toward the correct explanation.

The hypotheses that have been floated to explain this are of two types: Intrinsic and cosmic. The intrinsic hypotheses suggest that there is a gas leak or some other mechanical thing going on that changes the rate of the space crafts' movement. The cosmic hypotheses suggest that gravity works slightly differently than Einstein's model demands, and that this effect is very small but shows up in this particular case.

In the mean time, piles of data were sent back from Pioneer 10 and 11, used for various purposes, then slated for deletion because it was taking up too much space. However, Slava Turyshev, one of the discoverers of the Pioneer Anomaly wanted to analyze the data, and eventually, the Planetary Society raised the funds to save the data for Slava Turyshev and computer programmer Viktor Toth to play around with.

Now a large team of researchers is analyzing the data. They have created a model of all the systems on the space craft, and by analyzing exactly what was sent back, they are able to model the heat distribution from the Plutonium power source through various parts of the machinery on each probe in very fine detail. The idea is that the movement of heat around in the space craft changes the dynamics of its movement and could thus explain the anomaly.

So far the model accounts for about 30 percent of the observed anomaly for Pioneer 10 up to a distance of 10 astronomical units (approximately 1.5 billion kilometers) from the Sun, Turyshev reported. The group still has to extend the model to other distances and to Pioneer 11. The full verdict may not be in for some time. "I'm trying to ensure we apply every relevant piece of information," Turyshev says. "It is likely that the thermal explanation will explain part of the anomaly," he says, but exactly how much is up for grabs.

Now it is a waiting game as the team analyses the rest of the data. There is a distinct possibility that this very detailed model will not explain the slowdown in its entirely, which would leave open the possibility of a change in the gravitational model.

That's all very cool and interesting. So, how does this serve as a multi-plex lesson?

First, the data that were going to be thrown away may turn out to be useful, minimally, to refine the mechanical modeling and thus engineering of satellites, spacecraft, and so on. Don't throw away data! Second, nowhere in this story do you hear people denigrating, belittling, or even expelling scientists who are suggesting that a change in the dogma may be afoot. Einstein's gravitational theory is dogma in physics, and physicists are always questioning it. Darwinian evolution is dogma in biology and biologists are always questioning it. This crap about how we expel people who don't blindly accept the dogma is, well, crap. Finally, we have Click and Clack. Being MIT trained engineers, they gave a very good answer: No, when you are driving around in the convertible with the heat on, that heat was originally going to go out the exhaust pipe, and you are just redirecting it. But they also noted that technically, there would be small changes in something because you are moving around energy in some way. It turns out, though, that Click and Clack failed to mention that the movement of heat to different parts of the convertible than otherwise might happen could result in the long term trajectory of the convertible changing. A little.


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Re the convertible: they also neglect the electricity to run the fan which circulates the air through the heat exchanger (look, if we're going to be persnickety, let's go the whole way).

BTW#1: We have a Prius, and the internal heater is run by electricity, not by engine coolant (perhaps because you can't always count on the engine to be running?). What this means is that running the heater noticably dogs the gas mileage, which doesn't happen in a car that uses waste engine heat.

BTW#2: My DW is also an MIT trained engineer.

Yes, I was thinking about the fan as well. That is not a small amount.

Back in my satellite operations days I was doing day to day ops for APEX, the Advanced Photovoltaic and Electronics eXperiments. One day I walked into the payload area and one of the experimenters came up to me and said, "My instrument isn't giving me the numbers I expect." This guy was thrilled because he had something unexpected to look at, and possibly publish about.

I always think of him whenever I read something from the creationists about scientific dogma and scientific heretics being Expelled They just don't get how a scientist thinks. They've never seen the thrill in a scientist's eyes when he turns on his payload for the first time, or the heated arguments over what's going on. It's not like creationists think it is (or purport it to be) at all.

Hey Eamon,
What the heck is a DW? A divorced wife?

I'm not sure I'm understanding the mechanism, but from what I am gathering, what is happening is that when it is hotter in the front, the momentum from the black-body radiation from that area then slows the Pioneers? And when other parts are heated, it gives a slight push away then, too?

Wow, talk about precision measurements.

Another possibility I'm not sure I've seen anywhere would be the effect of dark matter. Wouldn't it tend to be slightly denser near the Sun and less dense farther away, so that our local measurements would be affected by that additional gravitational source, but the Pioneers, as they move out, would feel it more (not being contained within it as much)?

Pioneer goes at 27k miles an hour, and over 35 years they are about 8K miles short. That is not very much. So yea, black body radiation coming out the leading edge?

It is also the case that the deceleration in standard units is almost the same as the speed of light multiplied by the Hubble Constant. That is probably a coincidence.

But the effect is almost identical in both space craft. To me that rules out the gas leak explanation.

Aliens are messing with us?
How 'bout dark matter?
BTW, the article says 8,000 miles short a year; x35= 280,000 miles off. Still not a lot by interplanetary standards, but the chance of the difference in black body radiation between front and back supplying a significant acceleration seems small to me. These are not hot objects. And are they identical? If not, there's the same problem as with the gas leak theory: Why are the decelerations the same?

By uncle noel (not verified) on 17 Apr 2008 #permalink

Clearly, the galactic civilization, having detected our EM emissions from the early TV days, has placed Sol system under embargo. They are therefore directing long-range repulsor beams at anything mechanical emerging from our system.

Nobody wants Milton Berle showing up uninvited on their doorstep!

By Elizabeth (not verified) on 17 Apr 2008 #permalink

No, they're here! And they're looking for Milton Berle, whom they resemble. And slowing someone's spaceship down is a very meaningful gesture in their culture.

By uncle noel (not verified) on 17 Apr 2008 #permalink