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Review: The Pioneer Detectives

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The Pioneer Detectives: Did a Distant Spacecraft Prove Einstein and Newton Wrong?
by Konstantin Kakaes
The Millions, 2013
ebook, 65 pages

Almost anyone who has done some scientific research has experienced it: what might be called, colloquially if somewhat crudely, the “WTF?” moment. Data from a lab experiment or observations from a telescope turn up something completely unexpected. The first thing a scientist assumes, of course, is that something went wrong: an error in a procedure or a bug in software, for example. Most often that resolves the issue, but sometimes the anomalous data remains even after double- and triple-checking everything. That’s when the researcher’s excitement grows: has he or she made a fundamental discovery—or just missed a more subtle but mundane explanation?

That quest is the story of The Pioneer Detectives, a short ebook by Konstantin Kakaes devoted to what was known as the “Pioneer Anomaly.” That was the discovery, first noted in the late 1980s but not widely known until about a decade later, that the Pioneer 10 and 11 spacecraft were mysteriously slowing down. The two spacecraft, launched in the early 1970s, were speeding out of the solar system, yet it appeared from the data collected by NASA’s Deep Space Network that something was, in effect, tugging on the spacecraft. But what?

Kakaes tells the story of the Pioneer Anomaly primarily through two people. John Anderson was a navigator at JPL who was initially interested in the navigation data from the Pioneers not just to make sure the spacecraft were on course but also out of scientific curiosity, to look for evidence of gravitational waves. By 1988, he had detected the anomalous deceleration, initially thinking it might be evidence of dark matter. By the mid-1990s, more people were paying attention to the anomaly, including Slava Turyshev, a Russian physicist who came to work at JPL and was pulled into the effort to try and confirm the anomaly existed and, if so, what was causing it.

Kakaes eloquently writes about this scientific mystery, with asides on topics ranging from the Pioneer missions themselves to the plaques they carried to portraits of the key people involved.

The Pioneer Detectives follows the efforts of Anderson and Turyshev to first confirm that the anomaly wasn’t the result of a software glitch—a group from the Aerospace Corporation independently analyzed the Pioneer data and came up with a similar result—and then to understand what was causing it. There was no shortage of suggestions, which typically fell into two camps. One was that something with the spacecraft themselves, like leaking thrusters or radiation emitted from their radioisotope thermoelectric generators (RTGs), was slowing the spacecraft down. The other—and arguably more exciting—set of explanations revolved around some kind of new physics that the spacecraft’s decelerations had revealed, from modified Newtonian dynamics to, well, other ideas. (“‘Forehead collisions with gravitons,’ theorized a user [of the arXiv preprint server] from Belarus, whose grasp of physics was about on par with his grasp of English,” Kakaes wrote.)

At the risk of spoiling the question posed in the book’s title, the answer came from the former of those two camps: meticulous thermal modeling of Pioneer showed that the spacecraft’s deceleration could be explained by the way the spacecraft radiated heat: “[O]nce the thermal recoil force is properly accounted for, no anomalous acceleration remains,” Turyshev and colleagues wrote in a paper published last year. Newton and Einstein could rest easy.

Even if you’re familiar with the outcome of the Pioneer Anomaly mystery, The Pioneer Detectives is still a fascinating read. Kakaes takes advantage of the emerging “Kindle Single” format of short ebooks to tell a story that would be too long for a magazine article but too slim for a conventional book. He eloquently writes about this scientific mystery, with asides on topics ranging from the Pioneer missions themselves to the plaques they carried to portraits of the key people involved (Anderson, now retired, still believes some kind of exotic physics is at work, despite the conclusive thermal modeling.) It’s a fascinating reminder of how complex and challenging the scientific process can be, and how much work can be involved in determining if that “WTF?” moment will eventually result in an “ah ha!” or an “uh oh.”