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The energy produced by the atom is a very poor kind of thing. Anyone who expects a source of power from the transformation of these atoms is talking moonshine. Ernst Rutherford, 1933

2. THE PIONEER ANOMALY Previous | Next

Two spacecraft are flouting the laws of physics

BY RIGHTS, the Pioneer 10 and 11 space probes should no longer be of interest to anyone. Launched in the 1970s, they are now far beyond the edge of our solar system, drifting silently out into the void. The last contact we had with Pioneer 10 was on January 10, 2003, when a weak signal made it back to Earth. It is now nearly 8 billion miles away, past the orbits of Neptune and Pluto, and we will not hear from it again because it no longer has any power left with which to send out a signal.

However, the Pioneer probes are of interest. That is because they are drifting off course in a very intriguing way. In every year of travel, the probes veer 8000 miles further away from their intended trajectory. It is not much when you consider that they cover 219 million miles a year; the drift is around 10 billion times weaker than the Earth’s pull on your feet. Nonetheless, it is there, and decades of analysis have failed to find a straightforward reason, such as a heat leak from the probes. So it is possible that these errant spaceprobes are telling us something extraordinary. Maybe Newton’s law of gravitation, the law that describes how their trajectories should be playing out, is in need of an overhaul. Or is there is a new and strange force waiting to be discovered?

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#1 - Posted: 06/08/2008 19:07

On 8 December 1990, something strange happened to the Galileo spacecraft as it flew past Earth on its way to Jupiter. As the mission team watched, the spacecraft’s speed suddenly jumped by 4 mm per second. Nobody took much notice — a few mm/s is neither here or there to mission planners.

Then on 23 January 1998, the same thing happened to NASA’s Near spacecraft as it swung past Earth. This time its speed jumped by 13 mm/s.

The following year, Cassini’s speed was boosted by 0.11mm/s during its Earth fly-by.

People finally began to ask questions when the Rosetta spacecraft’s speed also jumped by 2 mm/s during its 2005 close approach.

Nobody knows what causes this anomalous step change in acceleration during fly-bys. However, it appears  fundamentally different to the Pioneer anomaly.

Earlier this year, a major peer-reviewed study from the Jet Propulsion Laboratory examined the data and pronounced the effect real. Which means we can expect to hear a lot more about it.


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Location:West Valley, Utah, USA

#2 - Posted: 07/08/2008 18:22

I suspect those spacecraft are behaving exactly as they should in the areas of space they happen to be in.  It may be that our observations are getting skewed because of variations in space and time where those spacecraft are passing through.  The radio signals from those spacecraft might be undergoing a phase shift because of a time difference instead of a frequency shif caused by motion.  Space and time might be different in front of the Earth than it is behind the Earth in its orbit.  Variations in speed as those spacecraft fly by the Earth might be an illusion whose magnitude depends on the spacecraft position as it flies by.  This is all speculation on my part, but the effect might be observed if an experimenter was looking for it. 

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#3 - Posted: 08/08/2008 10:24


I reported on the American Physical Society meeting in St Louis, Missouri back in April for New Scientist. One of the presentations was by Slava Turyshev, who is leading the official NASA investigation into the Pioneer anomaly. His painstaking studies indicate that nothing more exotic than heat emissions can account for at least part of the drift. Turns out that Pioneer 11 gives off heat in some directions more than others

which would push it off course. It only accounts for around a third of the drift, but it’s a start. They’re still looking at things like the spacecraft’s optical properties, and the heat drift might turn out to be enough to account for all of it. Anyway, my report on it is here      

There's a prototype of Pioneer in the Smithsonian National Air and Space Museum in Washington. I wondered if we might find out more about the craft's thermal properties by running a series of tests on it. But Turyshev reckons it would be too expensive to do and they simply don't have enough manpower. Also it's not clear that the protptype has exactly the same surface coating, so any results could be a red herring.


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