The Pioneer Anomaly: NASA Scientists Discovered Unexplained Forces Acting on Space Probes

NASA scientists are baffled when they discovered the "Pioneer Anomaly," where unexplained forces acting on spacecraft as they fly past Earth on their way out of the solar system:

Mysteriously, five spacecraft that flew past the Earth have each displayed unexpected anomalies in their motions.

These newfound enigmas join the so-called "Pioneer anomaly" as hints that unexplained forces may appear to act on spacecraft.

A decade ago, after rigorous analyses, anomalies were seen with the identical Pioneer 10 and 11 spacecraft as they hurtled out of the solar system. Both seemed to experience a tiny but unexplained constant acceleration toward the sun.

A host of explanations have been bandied about for the Pioneer anomaly. At times these are rooted in conventional science — perhaps leaks from the spacecraft have affected their trajectories. At times these are rooted in more speculative physics — maybe the law of gravity itself needs to be modified.

Now Jet Propulsion Laboratory astronomer John Anderson and his colleagues — who originally helped uncover the Pioneer anomaly — have discovered that five spacecraft each raced either a tiny bit faster or slower than expected when they flew past the Earth en route to other parts of the solar system.


The anomalous decelleration seen in Pioneer 10 was shown to be miniscule thrust from thermal radiation on the back of the spacecraft. This was a tiny, tiny effect, but noticable after 20+ years of mission. I don't know about the other four probes, but I wouldn't be surprise if something similar was going on.
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yeah, wouldn't you expect slight variations to what's planned, because it's not completely empty space?
i guess if the anomalies happen near earth then that needs a little more explaining but why presume it's a problem with gravity itself?
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Without knowing the the plane of reference of each object related to the Earth's magnetosphere, I cannot see how you could begin to make an educated guess as to the cause of the anomaly(ies). This looks like a job for a rocket scientist. But where could we find one?
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