Using Cassini to Test Radioactive Decay Rate Variation

Artist impression of Cassini orbiting Saturn (NASA)
Artist impression of Cassini orbiting Saturn (NASA)

In a previous Astroengine article, I explored the possibility that the variation in radioactive decay rates may be synchronised with Earth’s orbital variations in distance from the Sun. Naturally, this would be a huge discovery, possibly questioning the fundamental law that nuclear decay rates are constant, no matter where the material is in the Universe. One of the conclusions in the original decay rate research suggested that we should attach a sample of a radioisotope onto an interplanetary mission far beyond the orbit of Earth. By doing this, the relationship between decay rates and distance from the Sun should become obvious, and terrestrial decay rate variations can be tested.

But wait a minute, let’s have a think about this. Haven’t we already sent radioactive material on board interplanetary missions? What about all that plutonium we use to power interplanetary probes like Voyager, Pioneer, Galileo or Cassini? Plutonium is pretty radioactive… isn’t it?
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A Strange Connection: Could Nuclear Decay Rates be Influenced by Distance From the Sun?

The decay rate of the radioactive isotope 32Si appears to correlate with orbital distance from the Sun (Jenkins et al. 2008)
The decay rate of the radioactive isotope 32Si appears to correlate with orbital distance from the Sun (Jenkins et al. 2008)

Wouldn’t you think that the decay rates of isotopes found on Earth would remain fairly constant under controlled conditions? Statistically-speaking one would be able to make a pretty good prediction about a radioactive element’s decay rate at any point in the future, regardless of external influences. However, a group of researchers have found the radioisotope decay rates of radium (226Ra) and silicon (32Si) varies periodically. This may not seem strange at first, but when measured, this fluctuation in decay rate has a period of approximately a year. Does this relate to the Earth’s position in its orbit? Does this mean radioactive decay rates are influenced depending on how far the element is from the Sun? Perhaps decay rates are not as predictable as we think…
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