A scientific detective story if there ever was one, Slava Turyshev of JPL and his colleagues have spent years tracking down their villain, the Pioneer Anomaly: an unexplained acceleration in the motion of Pioneer 10 and 11, twin spacecraft that were launched by NASA in the 1970s and radar-tracked for over 30 years. Turyshev and his team have recovered files from NASA dumpsters, converted 1970s punch card data to digital, and spent untold man hours crunching numbers beamed to Earth decades ago from spacecraft billions of miles away.
Finally, the case is solved, and the villain is dead.
As the two spacecraft retreated into the distance, the data they beamed back showed that they were slowing down a little more than they should have been. Long vaunted as evidence that something was amiss in physics — perhaps that Einstein's theory of gravity was wrong — the anomaly spawned entire academic conferences and thousands of papers.
But, as explained in our coverage of an earlier stage of Turyshev et al.'s work, some scientists believed that the anomaly had a much more mundane explanation. Namely, the scientists suspected that heat was being emitted by the spacecraft's generators anisotropically — more in one direction than the other. If this were the case, the heat would exert an unbalanced recoil force on the spacecraft, causing them to change speed. Indeed, in April, a group of researchers in Portugal came up with just such a model for how the Pioneers' heaters could have created a recoil force.
But many have argued that the data itself ruled out this explanation for the Pioneer Anomaly. As the plutonium-238 that served as the Pioneers' onboard heat source radioactively decayed, it would have emitted less heat over time. Thus, if heat were the source of the Pioneer Anomaly, the anomaly should have lessened with time as well. But the data seemed to suggest that the Pioneer Anomaly was constant — an undying force — and thus much more fundamental.
But for their new analysis [PDF], Turyshev et. al. compiled a lot more data than had ever been analyzed before, spanning a much longer period of the Pioneers' flight times. They studied 23 years of data from Pioneer 10 instead of just 11, and 11 years of data from Pioneer 11 instead of 3. As explained in their new paper, the more complete data sets reveal that the spacecraft's anomalous acceleration did indeed seem to decrease with time. In short, the undying force had been dying after all, just like the decaying plutonium. In that case, it was most likely just a consequence of wonky heaters — mystery solved.
Science; it works. If only the Texas State Board of Education would take note...
ok... so which was it? Speeding up? or Slowing down?
" an unexplained **acceleration** in the motion of Pioneer 10 and 11..."
" the data they beamed back showed that they were **slowing down** a little more than they should have been"
" the more complete data sets reveal that the spacecraft's anomalous **acceleration**"
So they didn't know why they were speeding up, I mean slowing down, I mean speeding up. Really?
Playing Devil's Advocate since 1978
"The only constant in the universe is change"
-Heraclitus of Ephesus 535 BC - 475 BC
@codezero: technically an accelerations is only a change in velocity, so while deceleration is usually used for a negative change in velocity, acceleration is still correct, as the velocity has been changing.
Acceleration is a general term for any change in velocity whether speeding up or slowing down.
Also, a change in direction also could be considered accelerating; however, in this situation, it refers to slowing down.
They are using the term acceleration with its actual scientific definition, but yes, I s'pose it would be very easy to get confused by that.
@Josh_is_good Velocity is speed in a certain direction, so a change in direction is also a change in velocity. That's why acceleration covers that too :)
Consistancy in writing would have kept this fact clear, I read over the other article and the data sheet, and had that "ding" moment after reading the documents this was "inspired" by. I guess I have high standards for a scientific publication, shame on me. ;)
Playing Devil's Advocate since 1978
"The only constant in the universe is change"
-Heraclitus of Ephesus 535 BC - 475 BC
Code, I read this magazine everyday and it's got some great things... more good than bad for sure. However, this magazine does have a drawback for those who are more 'scientific' minded or looking for a 100% technically correct 'scientific publication'... it's 'Popular'. Hence the name. Actually, using the term 'acceleration' in this instance (when a change in velocity was being discussed) is probably one of the most scientific correct things in this article. Should we start using dumbed down words and colloquialisms? Doesn't very 'scientific' to me.
You know what? I rarely post comments on this site because I'm here for the articles not what the masses have to say about them... but you're on here everyday, stirring up the pot, trolling, badmouthing the authors. If they're so terrible go read Science, Nature, The New England Journal of Medicine... doesn't matter what, just something else! At some point it's not being the Devil's Advocate... it's just being a pain in the a*s. I'm pretty sure even the one you're advocating would be sick of it by now.
YAY A FELLOW TEXAN WHO SHARES MY BURDEN, it seems that texas just wants to avoid the problem by blaming schools for their fiscal issues and a reason for not using the rainy day fund, why else would u have one if you didnt use it for a rainy, like the one we are having
@Frosttty When has the Texas State Board of Education done something against physics?
I refuse to give all subjects of study the credit for what really belongs to only one. Just because physics is abundantly successful does not mean that paleontology or biology or psychology are. They are not all in the same state of development or insight.
@jbmshasta - Your comment was worth viewing this article.
if you think that biology is not well developed then perhaps you should not be going to the hospital or take medicine when you get sick or hurt, because every single treatment that you get there is a result of proven biology.
I'd wager that the issue at hand is that physics doesn't contradict your religious beliefs and biology and paleontology do.
it's no wonder that our country has lost it's edge in math and science. truly sad.
@codezero - Acceleration is equally applicable to both increases and decreases in velocity with respect to our frame of reference.
Further, it doesnt much matter in the context of the mystery whether the velocity was increasing or decreasing, the simple fact that it was changing without known cause was of interest. Had the anisotropic heat emmissions been biased back toward earth, then it would have been increasing in velocity more than expected, and we'd have been questioning our understanding of solar winds perhaps, rather than gravity.
Based on the article, we only know of something that *could have* caused the acceleration; there is no proof that it *did* cause it. As such, both the headline and the closing line are inaccurate and unsubstantiated.
"Consistency in writing would have kept this fact clear"
I don't see any inconsistency. If you knew what acceleration meant in the context of science, you wouldn't have been confused.
Everyone makes mistakes, but blaming others for your own ignorance is just sad.
To answer the question of what the article is talking about, the 'Pioneer Anomoly' is the name given to the unexplainable deceleration of the Pioneer spacecraft as they pass into the interstellar medium.
The article is saying that this decelartion is credited to 'anisotropic heat emissions' channeled in one direction generated by the spacecrafts' plutonium cores. The anisotropic emissions are the result of radioactive decay.
As the heat emissions decrease the spacecraft are now accelerating due to the lack of resistance created by the emissions and the fact that they are continually moving away from a large gravity source (i.e. planets, the sun and other debris) allowing for less gravitational restriction.
@redraobyek - Valid point. Rereading they do sort of make the statement with undue certainty. 'did indeed SEEM to decrease with time'. Seem is hardly the standard for putting an anomaly to rest. Certainly cause for more support to the idea though...
This article is a bit biased. When the Portuguese team solved this problem half a year ago they already got all the credit and actual headlines saying the problem was SOLVED. They provided the Solution. This JPL team is merely doing follow up work using larger time spans and more numbers. Seems more like they are trying to save face. After spending so many years on it and then having the Portuguese provide the actual solution. Can only have been a nightmare for them.
@pheonix1012 i think you may be mistaken, the pioneer spacecraft would be moving at a constant speed due to intial thrust, this speed would be constant untill another force moved it in another direction, in this instances the heat from the plutonium, so the speed slowed down, if the heat were to be removed the speed would not increase because there is no force to make it increase, a lack of force does not cause an increase in speed, there is no constant force being applied to this craft.
@Ianredneck - There are always forces at work, the question is whether their magnitude is enough so that the effects are no longer negligable. Gravity is ALWAYS in play. There are also interactions with particles emitted by the sun.
Not really sure at this scale whether either are negligable or not, to be honest... but I suspect that is the reason for the distinction 'unexplained acceleration', rather than just acceleration.
@iambronco agreed but the post made it sound like that a lack of force will increase the speed of the craft
@lanredneck - It does, doesnt it... Point taken. To be honest, I'm not really sure who asked the question pheonix was answering. I think everyone knew what the article was saying... only question was about the use of 'acceleration' in reference to reducing speed.
Now that the acceleration issue is cleared up. Why would people who believe the bible be on this site? Physics also contradicts the bible. Only science or the bible is correct, not both. The bible contradicts ALL science and itself. They did teach Greek mythology in world history. Maybe if Christianity was 1000 times more interesting it could have place in world history 1000 years from now. Jfc. I'm sorry. But seriously. Answer to the anomaly. God works in mysterious ways, duh. I'm just sticking up for our amazing universe that you feel the need to credit to a fairy tale. Like saying I crap out your babys. I think I may actually. Gotta go #2 for an expecting couple. Maybe science will prove I don't crap Christian children. It don't matter, teach it anyways. Would you like me to send you a sample?
I do apologize, off topic and irrational behavior. Religion and politics always get me.
That truly is the answer to everything though, god works in mysterious ways. Wtf.
This is not a serious article. That thermal effects were at the origin of the anomaly was suggested since early on by Katz and Scheffer, but the JPL team dismissed this explain as they claimed that the anomalous acceleration was constant. Now they claim otherwise, on the basis of new data. Is this data public? If not, this is not science. And there is also earlier work showing that the acceleration can be explained by thermal effects (http://arXiv.org/abs/arXiv:1103.5222) . Once more, if that work is not mentioned this is not serious scientific work.
In this case, there is no proof, no absolute, just evidence and an opinion. This kind of article is quite informative but does science and the public a disservice by playing fast and loose with what is and is not proven.
This is a real problem across the whole broad expanse of the information media right now. Truth is often replaced by untruth or halftruth, in the form of opinion, that is then installed into the public as perception.
Terms like 'case closed', 'end of story' and 'mystery solved' are powerful tools when applied to a trusting readership.
They, and we, shouldn't be abused.
@dditto2: No one even mentioned religion, so why bring it up? There are plenty of Christian scientists out there that obviously see things a little differently from you. Being closed minded doesn't make you right, try to be a little more respectful of other people's beliefs.
jbmshasta - like Purple Leaves, I just want to say thank you for posting that. = )
Ah, what a wonderful thing science is! So pleasing for someone learning to drive to discover that the accelerator and brake pedal can be used interchangeably!