G+ Research Story #7 | Space mystery solved after 32 years! The Pioneer Anomaly

Note: Carl Sagan's diagram on this post was temporarily censored by G+. More details here: goo.gl/ZAj11

▶ It all started in 1980 and then had a boost in 2005...

Something strange is happening in the outer reaches of our solar system. The Pioneer 10 and 11 spacecraft are not where they are supposed to be. These missions, launched in 1972 and 1973, have covered hundreds of millions of miles, heading toward the edge of our solar system. But something is holding them back. Each year, they fall behind in their projected travel by about 8,000 miles.
Scientists are being forced to consider the unthinkable: something may be wrong with our understanding of The Laws of Physics.
Jet Propulsion Laboratory scientist Dr. John Anderson and his colleagues have been searching for an explanation since 1980. But as of yet, they have found nothing conclusive.
The trajectories of these two spacecraft were deviating from the known laws of motion, the laws given to us by Newton and Einstein, and "losing" about 8,000 miles in a year. And...that figure keeps growing!

▶ They got closer to the solution in 2011...

Scientists working with recovered data from the Pioneer 10 and 11 missions are closing in on a solution to the famous Pioneer Anomaly.
Their just-published results show that the mysterious effect on the two spacecraft is not constant over time, probably indicating that no outside force is acting on the Pioneers, but rather, something inside the spacecraft is to blame.

▶ And finally cracked it in 2012!

It's been a long and winding road, but Slava Turyshev and his colleagues have just explained the anomaly causing the unexpected slowing of the Pioneer 10 and 11 spacecraft.
It's due to anisotropic thermal radiation, that is, when the spacecraft emits more heat in one direction than the other.
Why was the thermal emission from the spacecraft anisotropic and slowing the spacecraft down?
First of all, because the Pioneer spacecraft were spin-stabilized and almost always pointed their big dishes towards Earth.
Second of all, because two sources of thermal radiation (heat) were then on the leading side of the spacecraft.
The nuclear power sources, more formally Radioisotope Thermoelectric Generators (RTG), emitted heat towards the back side of the dishes. When the dishes reflected or re-radiated this heat, it went in the direction of travel of the spacecraft.
Also, the warm electronics box for the spacecraft was on the leading side of the spacecraft, causing more heat to spill that direction. Photon pressure, the same type of thing used in solar sailing, then preferentially pushed against the direction of travel, causing a tiny, but measurable, deceleration of the spacecraft – the Pioneer Anomaly.

Recommended articles by The Planetary Society

2005.05.10 Solve the Mystery -- the Pioneer Anomaly: goo.gl/Zomed
2006.06.01 Data Saved! goo.gl/7wRbq
2011.07.22 Pioneer Anomaly on the Verge of Solution: goo.gl/cznTh
2012.04.19 Pioneer Anomaly Solved! goo.gl/zRaFh

Extra: A Graphic Designer's Guide to The Pioneer 10 Plaque

(Disclaimer: I'm a member of The Planetary Society since the 90's)

#pioneer10 #pioneer11 #pioneeranomaly #heat #mystery   #GPlusResearchStories  

Cc: +Emily Lakdawalla +michael interbartolo +Rich Pollett
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