Pioneer 10's Quirky Path Through Space Poses Compelling Mystery For Physicists

By Frank T Kryza

On March 2, 1972, a balmy Thursday on Florida's humid Cape Canaveral peninsula, a NASA Atlas-Centaur rocket took off with a 570-lb payload called Pioneer 10. Pioneer was a space probe designed to cross the asteroid belt and perform a "fly-by" of Jupiter and the outer gas giants to study them. For the next ten years, Pioneer sent back astonishing reports from the far reaches of the solar system, carrying out its mission with great success.

Then, instead of falling silent as it had been expected to do, Pioneer kept sending signals back to Earth. Its tiny nuclear generator kept cranking out the 70 watts of power needed to maintain a radio link with the Jet Propulsion Laboratory in Pasadena, California, and this continued for decades longer than anyone believed possible. Communication kept up on a daily basis until January 23, 2003, more than thirty years after the mission began. By then, the probe was twice the distance from the sun as Neptune and Pluto are, and Pioneer had become the first object made by the hands of man ever to leave the grip of the sun's gravity forever.

The Pioneer story would have been a significant chapter in the history of science had it ended there, but it did not. Experimental physics is full of examples of scientific projects designed to study one phenomenon yet revealing unexpected truths about something else entirely, and the really interesting piece of the Pioneer 10 story is one of these. Though it had carried out its robotic exploration of Jupiter and Saturn with skill and perseverance far beyond the call of duty (if one can apply such language to a robot), by the time it was passing the outer limits of the planetary system, it was clear to NASA that it was hundreds of thousands of miles from where computer tracking programs said it should be. How was that possible?

The way objects move in space, whether they are planets the size of Jupiter or tiny craft like Pioneer, is governed by well-known laws of physics that give precise answers about location that can be measured in centimeters, even on the scale of the solar system. For Pioneer to be hundreds of thousands of miles off course was simply not possible. No matter how it was tackled, the problem just wouldn't go away, and it soon became clear that something truly weird was going on. NASA scientists gave this quirk of Pioneer a name; they called it "The Anomaly."

"The Pioneer Detectives: Did a distant spacecraft prove Einstein and Newton wrong?" a newly issued "Kindle Single" by Konstantin Kakaes, a gifted journalist and writer who studied physics as an undergraduate at Harvard, explores the tantalizing clues scientists uncovered in seeking to explain the Pioneer course deviation. The deeper they dug, the less they seemed to understand. Immersed in the daily tracking logs of the 30-year-old space probe, startling and perhaps revolutionary questions began to emerge: Was the spacecraft's errant course proof of some new and unknown wrinkle in the fundamental laws of physics?

A slightly off-course spaceship may seem an unlikely subject for deep speculations about the fundamental nature of the universe, but obvious solutions to Pioneer's flight deviation were not forthcoming. Yet this was a matter of "black letter" physics, and errors of this kind and of this magnitude just cannot occur.

What could be the cause of "The Anomaly"? The NASA sleuths could not seem to agree, though the list of possible culprits was long and scary: Dark matter? Tensor-vector-scalar gravity? Collisions with gravitons? A fundamental error in Einstein's equations?

The only thing clear about the questions posed by Pioneer and "The Anomaly" was that potentially groundbreaking discoveries were in the offing for those brave enough and smart enough to tackle them successfully. This is territory young scientists call "new physics" -- an unmapped land where new Nobel Prizes are sometimes also found.

Writing in clear, sharp prose free of technical language, science writer and former Mexico City bureau chief for "The Economist" Konstantin Kakaes gives us a spine-tingling scientific detective story, tracking the mental processes and the spadework of those committed to untangling this high-stakes science enigma. Kakaes draws on extensive interviews and archival research, following the story from "The Anomaly's" initial discovery through decades of tireless investigation, to its ultimate conclusion. "The Pioneer Detectives" is a riveting and definitive account, not just of the Pioneer Anomaly but also of how scientific knowledge gets made and unmade, with scientists sometimes putting their reputations and their livelihoods on the line in pursuit of cosmic truths.