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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:

▶ 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:
2006.06.01 Data Saved!
2011.07.22 Pioneer Anomaly on the Verge of Solution:
2012.04.19 Pioneer Anomaly Solved!

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
Kenneth Holand's profile photoDeborah Teramis Christian's profile photoQ'ouarin Unicorn's profile photoYin Huang's profile photo
Thank you all for sharing such a fascinating tale of data gathering, digital preservation, telemetry analysis and human perseverance.
This is what science is all about!
Why is the first thought that something is wrong with the laws of physics? The reason is for hype. If the rules appear broken do not first assume the rules are wrong. Assume the data is wrong, assume the measurement system is wrong, etc. Always start small and see what shakes loose before deciding that they "consider the unthinkable". My two cents...
We should launch more sophisticated probes out the solar system. One that can travel faster and with more high tech equipment. That would be interesting XD. Who want's HD photographs of our entire solar system? I DO!!
Agreed, +Levi Richards. The simplest explanation is often the right one :) Occam's razor in action :)
Occam's razor is the law of parsimony, economy or succinctness. It is a principle urging one to select among competing hypotheses that which makes the fewest assumptions and thereby offers the simplest explanation of the effect.
▶ Correction: see +Tiaan Kruger's clarification below about Occam's razor
what about Voyager I & II, they have not slowed down. Why?
+Ricardo Nuno Silva no, that("The simplest explanation is often the right one") is not what Occams Razor means. often misquoted(especially in movies) to mean what you said. look at you post you put under that sentence. It means that you shouldnt make ASSUMPTIONS(which leads to false or misleading information). and thereby simplify your data set, and thus your explanation, and it ends up the more accurate one. You could for example give a VERY simple explanation but 1 variable is fact,the other is assumption. a explanation that has 3 variables that are known for a fact is more likely to be right, as it "makes the fewest assumptions"
so it is not about the explanation being simple, it is about the assumptions being less(which mostly leads to a simple explanation
Aliens. Aliens are holding them back.
It could be god saying you have wandered off to far into my world.
As fast as they are traveling is 8000 miles really that significant?
Thanks, +Tiaan Kruger, for the useful clarification about the distinction between assumptions and explanations in Occam's razor. 5*!
+Quinton Hanson it is not the fact that it is a lot or not. But there were not exactly at the place that we were expecting !
this problem had almost made us need to put einstein and newton theory in the garbage so yes it was a serious problem.
I am happy that it is finaly resolved.
+nathan sanders The photo represents the plaque attached to each of the Pioneer probes:

The Pioneer plaques are a pair of gold-anodized aluminium plaques which were placed on board the 1972 Pioneer 10 and 1973 Pioneer 11 spacecraft, featuring a pictorial message, in case either Pioneer 10 or 11 is intercepted by extraterrestrial life.

The plaques show the nude figures of a human male and female along with several symbols that are designed to provide information about the origin of the spacecraft.

The Pioneer spacecraft were the first human-built objects to leave the Solar System. The plaques were attached to the spacecraft's antenna support struts in a position that would shield them from erosion by stellar dust.

+Vincent Fernandez We shall send nothing more outside our solar system. What if Native American sent message via the Gulf Stream revealing their presence in 1200? They would have been exterminated earlier.
So we Native Earth shall preserve ourself and stop this silly "please come here, we have a lot of slaves and resources"

Perhaps if the Roman Empire met the Mayan before the Aztecs, Maya culture might have not been wiped out... ok.
My point is, we don't know who is going to read that message, and what intention he/they might have.
+Pietro Branca Thank you for referring what's possibly one of the most plausible fears in projects to contact alien civilizations, like SETI projects, deep space transmissions and messages in space probes.
In fact, no one can assume that alien civilizations, if they exist, will have peaceful intentions towards Humanity. That scenario has often been portrayed in sci-fi movies in the last decades.
Anisotropic thermal radiation? I don't exactly buy into that. It opens up so many other questions. I am trying to recall my Physics lessons which I mostly yawned my way through but, I recall something about the theory of space sails being that the proton particles of the sun pushed the craft. Probably an overly simplified recall. So, in my process of interpretation of the solar sail theory, the farther from the sun an object travels the slower the rate of propulsion? In that case I would expect them to slow somewhat the farther they travel from the Sun. Unless of course God or Aliens are doing it, THAT cannot be ruled out... ;)
Then why not spin them around and use the heat as propulsion? Only turn them back when they need to send or recieve?
+Quinton Hanson Those 8,000 miles may seem like a small distance in astronomical terms but this kind of anomalous deviation can have impact while managing planetary missions. It may affect many calculations like: radio transmission windows, antenna and cameras positioning, planetary trajectories, orbit insertions, fly-bys, etc.
Interesting directions this conversation has gone in. I agree with +Chris Lichowicz . In fact, I started to say something similar before I read his comment. Seems you've beaten me to the punch yet again.
+Teri Ondracek This kind of small anomaly cannot be detected in the Voyager probes (and other missions) using the same methods:

"The Pioneers were uniquely suited to discover the effect because they have been flying for long periods of time without additional course corrections.
Most deep-space probes launched after the Pioneers either stopped at one of the planets, or used thrusting throughout their mission.

The Voyagers flew a mission profile similar to the Pioneers, but were not spin stabilized.
Instead, they required frequent firings of their thrusters for attitude control to stay aligned with Earth.

Spacecraft like the Voyagers acquire small and unpredictable changes in speed as a side effect of the frequent attitude control firings. This 'noise' makes it impractical to measure small accelerations such as the Pioneer effect; accelerations as large as 10−9 m/s2 would be undetectable.

Newer spacecraft have used spin stabilization for some or all of their mission, including both Galileo and Ulysses.
These spacecraft indicate a similar effect, although for various reasons (such as their relative proximity to the Sun) firm conclusions cannot be drawn from these sources."

+Chris Lichowicz / +Daniel Golightly Yes, these recent findings may also help building deep space probes with optimized thermal configurations for better long range performance :)
In deep space every temperature degree counts ;)
+Ricardo Nuno Silva Are such fears truly plausible? Beyond the small chance that we will physically encounter other intelligent life in the galaxy, what would be the purpose of conflict with Earth? We have no unusual natural resources that are worth the trip and anything an enslaved human can do an automated machine can do better. We might not even be habitable to ET life; why fly through space for so long just to kill something? At best, it seems we're inflating our own importance in the universe.
+John Cromie Yes, we usually inflate our own importance in the Universe. It's in the human nature, I guess ;) But we should ponder that cosmic distances vary according to the technology used to travel...
So we may not be "as far away" as we suppose (or wish for ;)
reading this just made me high. Happy #420 from a non-smoker.
+Ricardo Nuno Silva I agree that we can't predict how advanced space travel technology will become; it may be possible to quickly traverse the long distances of space. My question is: what would be the point? Even though we have cars and planes, we still go grocery shopping someplace close rather than drive/fly to another state. Of course, I suppose this assumes other life is not psychotically xenophobic or as lazy as we are.
I guess we can only hope other living things would rather just have a pint and watch a some TV.
+John Cromie The enslave/resource is just an example. What was the purpose to conflict with Iran, Iraq, Vietnam? What's the purpose of killing small seals? We might became a delicious meal, some fine leather jackets, or a giant "aquarium" perhaps a huge science sandbox.

The hyperbole is obvious, let's deflate our importance... maybe to them we are like fishes in a tropical atoll... let's call it Mururoa.

The chance that it reaches some evil hyper-tech ET is so small that we should nearly ignore it. But keep sending messages to the outer space is not a good idea, not yet.
+Dana Morris It is moving slower because the radiation from inside the "engine plant" of the probe is pushing off the radio antenna in the opposite direction of the probe's path. (This is in general terms and may or may not reflect(ha ha) actual reality since there are several other factors).

...First assume a finite elephant...
still confused as to what the diagram is actually showing, but that man should be embarrassed.
+Levi Richards For me, the image is... black. After requesting the review, I got this message on screen:
Google+ has received your request and is reviewing this image and album.
In the meantime, you can still view, download or delete this image. Sharing is disabled pending the results of the review.
If the image is okayed, its original visibility will be restored, sharing will be re-enabled and this message will be removed.
I guess I narrowly escaped censorship with my last post on plant porn ;) Do you think someone lodged a complaint or is this some automated image detection at work?
What a shame, you have my sympathy.
Fantastic post, I can't believe this was sensored for a bit. Seems to be uncensored now.
We need a systems person to explain how that can happen! We must be reading different caches or something.
I do not see the censored image... for me, your original image is all there... even those 'rude bits'.
i refreshed many times but i see the original image.
could it be that it's back?
Re: Occam “What can be done with fewer assumptions is done in vain with more.”
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