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What's Slowing the Pioneer Spacecraft? -Pondering a Mysterious Force

Pioneer_spacecraft_3 What goes up must come down - unless you throw it hard enough.  That's the lesson learned by four man-made objects to date, the Pioneer and Voyager space probes flung into the heavens to go where no man has gone before.  These grandfathers of gadgetry could still kick your iPhones whippersnapper of an ass with both high-gain antennae tied behind their back - they've gone above and beyond their functions in ways that make John McClain look like a wimpy quitter.

Pioneer 10 and 11 were launched in the early seventies.  They carried scientific instruments deep into the solar system, probing the asteroid belt , giving us our first close looks at Jupiter and Saturn and blazing a trail that the Voyager probes would follow.  These enduring explorers couldn't be returned to the store for repairs and were McGyvered together by remote control for years of their operation, rerouting power and running backup components while the only special sensor your new phone has triggers a self-destruct the instant it detects your warranty has expired.  Now, long after completing their intended missions these astronomical adventurers are giving scientists plenty to think about with the "Pioneer Anomaly"

Their voices from the dark may have gone silent years ago, but scientists have kept track of the pioneer probes with doppler radio - bouncing electromagnetic waves off the distant devices to learn their speed and position (it's quite natural that after thirty years of tracking their electronic offspring, the scientists become concerned when they stop calling home).  The "Pioneer Anomaly" is the discovery that these probes are slowing down very slightly more than they should - and nobody knows why.

One thing this deceleration can tell us for sure: don't try to rip a scientist off over small change.  The measured deceleration is about one nanometer per second per second, measured over distances of about seven trillion meters.  That's twenty-one orders of magnitude between the length scales.  That's a thousand billion billion to one, a sextillion to uno, a fleetload of boatloads to a thimbleful and a whole bunch of other things I could say but won't, because unless God is reading this with a calculator in His hand there's no mind that can process that kind of scale.

This submicroscopic measurement has attracted global attention, with dozens of theories put forward to explain the discrepancy.  From the mundane like gas leaks from the satellite or uneven heating of the probe, to universe-bending descriptions involving superstring, dark energy and relativity all rolled up into a probe-pulling shape. Inevitably the crackpots have been attracted as well, holding forth that the Pioneer slow-down can be simply and easily explained by their own personal view of the universe - the only slight problem being that nothing else can unless you ask them specifically and give them a few minutes to think of an answer.

Obviously with such a tiny value being held forth as a reason to re-evaluate relativity, people want to make sure they measured it right.  An effort is currently underway to convert and analyse all the recorded data in a single format, reducing the possibility of statistical errors or the effects of changing how the data was recorded over the years.  And after thirty plus years of barrelling through space, it's ironic that they're now racing against time - to translate the data before the only remaining machines that can do it are scrapped, or the only people left who can run them die of old age.

One thing is for sure - whatever the answer, we won't be able to share it with the probes that raised the questions.  Pioneers 10 and 11 have passed the last point of possible communication with Earth, their antennae having lost the way home and their reactors run down.  But even blinded and cold they carry out one last mission for mankind, ferrying plaques bearing a message of welcome and a pulsar map to the home of the monkeys who managed to hurl tin cans and wiring into interstellar space.  They're expected to arrive at neighboring stars sometime in the next five million years - assuming as they don't run into any Klingons first.

Posted by Luke McKinney.

Related Galaxy posts:

The Dark Secret of the Cosmos
"The Elegant Universe" -A Galaxy Insight
Cruising the Goldilocks Zone -The Search for "Super-Earths"
Non-Carbon Lifeforms -Why We May Overlook
The Milky Way Enigma -How Galactic Forces May Control Life on Earth

 Astro-Engineering Artifacts as Evidence of
The Biological Universe -A New Copernican Revolution?
"42": Hitchhiker's Guide to the Galaxy Foreshadows Actual Weight of Universe!
Andromeda Galaxy & Its Mystery Core: Destined to Merge With the Milky Way?

The Planetary Society Pioneer Anomaly Effort

A modified gravitational theory

An "Electrical Theory"
Re: Electrical theory: Seven tips for spotting bad science


If you are going to use big numbers in 'scientific' articles, the least you can do is to use the
appropirate scientific notation, i.e. not one billion years but ten raised to the power of nine (expressed in numerals).

The slow down? Nothing more than Einstein's theory of relativity
proving that time slows down with
speed. Brilliant, isn't it?

Submittted - Barrie O'Leary, Queensland

I dont think barrie knows what hes talking about

luke has been my favorite science article writer so far you know.. cool, Luke!..i loved this one too

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