Thirty years ago, NASA scientists noticed that two of their spacecraft, Pioneer 10 and Pioneer 11, were veering off course slightly, as if subject to a mysterious, unknown force. In 1998, the wider scientific community got wind of that veering—termed the Pioneer anomaly—and took aim at it with incessant, mind-blowingly detailed scrutiny that has since raised it to the physics equivalent of cult status. Now, though, after spawning close to 1000 academic papers, numerous international conferences, and many entire scientific careers, this beloved cosmic mystery may be on its way out.
Slava Turyshev, a scientist at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., and Viktor Toth, a Canada-based software developer, plan to publish the results of their strikingly comprehensive new analysis of the Pioneer anomaly in the next few months. Their work is likely to bring a conclusion to one of the longest and most tumultuous detective stories of modern astrophysics.
NASA launched Pioneer 10 in the spring of 1972 and Pioneer 11 one year later. The spacecraft's joint mission was to gather information about the asteroid belt, Jupiter, Saturn (in the case of Pioneer 11), and their moons. As they hurtled past those various celestial objects, the probes measured previously unknown properties of their atmospheres and surfaces; they also photographed Jupiter's Red Spot and Saturn's rings up close for the first time. Then, after completing their "flyby" missions in the mid-1970s, the Pioneers kept going. Carrying identical plaques depicting a man and a woman, the atomic transition of hydrogen, and the location of our planet within the galaxy—a message to aliens—the probes became the first manmade objects ever to plunge beyond the solar system into the inconceivable cold and dark of interstellar space.
JPL scientists continued Doppler tracking the Pioneers far into deep space. They sent and received a continuous stream of radio transmissions to and from both Pioneers, logging the velocity of each everywhere along its trajectory. An astronomer named John Anderson led the analysis of the Doppler ranging data. He and his team intended to use the data to study subtle gravitational effects in the outer solar system, far from the overwhelming influences of the sun and larger planets. It was thought, for example, that the Pioneers might oscillate in tune with low-frequency gravity waves.
Of course, in order to detect such curiosities in the motion of the spacecraft, the scientists needed to know exactly what to expect in the first place; this required the construction of an algorithm of truly staggering complexity. Contributing factors to the predicted Doppler shift included: the deceleration experienced by the Pioneers as they struggled against the gravitational pull of the sun, planets, moons, asteroid belts, and comet clouds, the positions and thus gravitational fields of which move constantly; the tiny push on the spacecraft by the sun's radiation, which weakened with time as the spacecraft moved progressively farther away, and also changed as the angle of the spacecraft changed; the increase in the delay time between the bounce of a radio wave and its reception back at Earth as the spacecraft grew more distant; the gravitational drag on the radio waves from the sun; the additional frequency shift in the radio transmissions caused by the rotation of the Earth… and the list goes on. Anderson synthesized that headache's worth of cosmic influences into a single algorithm. But unfortunately it didn't seem to work.
In 1980, he noticed a small discrepancy between the Doppler shifts he expected to receive based on his algorithm and the actual, measured shifts of the radio signals coming from the spacecraft. Their expected and actual motions weren't quite matching up. As they moved outward against the gravitational pull of the sun and planets, the spacecraft were, of course, slowing down. But the problem was they were slowing down too much. Each year, both of the spacecraft were a few hundred miles farther behind where they should have been on their respective paths, according to the algorithm. That isn't much in the context of space travel, to be sure, but it isn't trivial either. The constant, extra acceleration amounted to 8.74 x 10-10 m/s2 directed toward the sun– a factor ten billion times smaller than the acceleration due to gravity, but still, undeniably, there.
Anderson's first reaction was to think his algorithm must have been missing something. Some tiny influence on the motion of the spacecraft must not have made it into the mathematical mix. A few years of thinking and discussing led him and his immediate team to the conclusion that the anomalous acceleration must have been caused by "outgasing" - fuel dripping from the thrusters, exerting a recoil force against the spacecraft as it dripped. Since by that point the craft were cruising through interstellar space without propulsion, the scientists thought the fuel drops would soon finish dripping and the effect would go away. But perplexingly, it didn't: Over the next decade, the spacecraft racked up billions of frequent flier miles--but thousands less than they should have.
In 1994, Anderson received an email out of the blue from Michael Martin Nieto, a cosmologist at Los Alamos National Laboratory near Santa Fe, NM. Nieto had lately become interested in alternatives to Newton's inverse square law for gravity, including a new theory called MOND (modified Newtonian dynamics), and so he contacted Anderson to find out how sure NASA was about the strength of gravity based on their observations of the motions of spacecraft. Anderson replied that, as a matter of fact, gravity didn't seem to be working right for the Pioneers.
When Nieto read the exact value of the small, anomalous acceleration experienced by Pioneers 10 and 11, he almost fell off his chair. (In typical physics-speak: "My office had a hard floor and my computer chair had wheels, so when I arched my back in a "wha?" reaction the chair started rolling.") There was a profound cosmic coincidence afoot: As Nieto immediately noticed, the value of the Pioneer anomaly almost exactly equaled the so-called "cosmic acceleration"—the speed of light 'c' multiplied by the Hubble constant 'H'—suggesting the anomaly's cause lay within the foundation of physics.
Right then and there, Nieto signed on to work with Anderson at JPL, got a major investigation of the Pioneer anomaly off the ground, and has spent most of his energy studying it ever since. Why? "The Pioneer anomaly could be the first evidence that gravity deviates from an inverse-square dependence," he said recently. "It could be huge."
Interesting article and very revealing in one issue regarding mankind: stubborn persistence and extreme need to know the truth.
Great writing! And also great images - that last illustration of the pioneer really hits home how romantic some of our ideas about space really are.
Very intersting reading, I'm sad to find out that the abnormal drag originally slowing down the craft was not a giant cloaked ship sent here to study us...
Wow! Awesome, well written, science based article!
I can't wait for your follow up article when they publish peer reviewed details....
Coolige said it well, "...persistence and determination alone are omnipotent..."
Great article. The in-depth look at what they are doing to solve this problem is a great refresher to the usual blurb articles that we usually see.
I am happy to say that I spent some time at work reading this.
very well compiled article.. u piqued my interest in the Pioneer spacecraft for sure ;)
XD nice antispam measures too popsci! :D
It was like reading a script to a movie.
Natalie Wolchover, I think you should write a book about this after the final details are released.
The article was inspiring actually, the home computers, the colaborations, the great unknowns...excellent!
Now it's time to get back to work on my own anomylies.
I was expecting a quote from Sheldon Cooper or Rodney McKay. Great article! My head hurts just thinking about all that math!
Great article and a real joy to read!
Thanks Pop. Sci. and great job Natalie Wolchover.
She deserves a raise.
This is the kind of great writing I look for in Pop. Sci. Mag.
Yes, excellent stuff - felt a bit like NOVA, no offense intended, of course.
Everyone is saying "excellent, great article" I just say long and confusing.
There was an article a while back that theorized that the farther you go into space then matter's parameters to be stable changes. Could simply space's "grid" (the grid in all the explaining gravity images) be distorted like unaligned crossing toothpicks.
(can't make diagram with font) >:(
Or have just jumped the gun on theorizing what someone else thought or spent years on?
I have been under the impression that Voyager was further out than Pioneer? NASA appears to believe this as well... if one is to accept that the article posted on PopSci yesterday at least.
"Voyager 1 launched in 1977 mind you – is now poised to become the first man-made object to leave the solar system for the larger galaxy beyond."
That, taken in context with this article, "the probes became the first manmade objects ever to plunge beyond the solar system into the inconceivable cold and dark of interstellar space." just seems a bit off to me.
Does anyone know what source reports Pioneer as being in interstellar space? It bothers me that I have believed for some time that Voyager was going to be the first to officially breach the solar system.
Excellent article by Natalie Wolchover. This is the kind of intelligent, in-depth science reporting that I want to see in the pages of Popular Science. There have been too many gee-whiz articles with little critical analysis in the past, and this shows that PopSci readers do appreciate detail and thoroughness. Bravo, Natalie!
Just becuase physics works on earth why should it be the same far way? Remember 600 years ago the earth was flat and everything revoled around it.
That was exceptionally nerdy and fun. I was reading it like a movie and expecting the laws of Newtonian physics to come crumbling down at the edge of our solar system. While reading, I started to imagine my own explanations, that gravity might begin to flux or curve in disorder further out, or that heat generated in the absence of gravity becomes parasitic to motion.
Mightn't we be looking at an effect of gravitational lensing?
A possible explanation for this fascinating anomaly ...
Article: What Causes the Mass to be Deficit Inside a Nucleus?, Prespacetime Journal, Vol. 1, Issue 9, November 2010, Available at http://www.prespacetime.com/index.php/pst/article/view/123
Anyone else think it was a bad idea to include the location of our planet on the plaque that was sent? I hope the aliens that find them are not conquerors.
It depends on the definition of 'leaving the solar system'. Pioneer 10 and 11 were the first probes to pass beyond the orbit of Pluto, then considered to be the last planet in the solar system. If you define 'leaving the solar system' as passing the orbit of Pluto (or now Neptune), then Pioneer 10 holds the distinction of being the first to leave the solar system.
Some people however define it as passing the point at which the sun no longer exerts any influence on the spacecraft. In that case then Voyager 1 and 2, although launched well after the Pioneer probes but are traveling a lot faster, will be the first to exit the solar system based on that definition. The Voyager craft passed the Pioneer craft sometime in the 90's. So yes, Pioneer 1 and 2 are the farthest man made craft in space, but only because they were traveling faster than Pioneer, not launched before Pioneer.
Have they thought about the amount of space crap this thing is running into?
You only get the data if you carry the sorry asses at the top of the dust up along with you on your back as dead weight, contributing nothing at all. The old records are probably questionable as anything of that age being translated must be. What's next? Parallax error on old equipment, rounding errors in the old language integrators? This controversy will be solved when these old probes reach infinity, i.e. never.
I face the same problem in my work. I've found the cure for drug addiction, it's the grease on a man's face--a pheromone passed in kissing. There's about five million advanced google entries under 'the cause of love' all of which are wrong. Try telling that to a scientifically illiterate reviewer with a psychobabble degree. No you are not getting funded. "But I have changed the sexual orientation of people with pheromones, famous people!" No. That's impossible. "Look at my dozens of anecdotes!" Anecdotes mean nothing, go away.
An effective, broad-spectrum medical treatment for borderline personality disorder, suicidal ideation, drug addiction, delinquency, and perversion has been discovered. It is a human pheromone, the healthy adult male facial skin surface lipid 'kissing daddy' pheromone. Unfortunately and presumably due to differing metabolic/neuronal pathways, alcoholism is little effected by pheromone treatment. One dose of 150-250 mg provides permanent relief of even the most obdurate cases.
Nicholson, B. 1984; Does kissing aid human bonding by semiochemical addiction? British Journal of Dermatology 111(5):623-627.
Nicholson, B. 2009: Of Love ( Amazon Digital Services, www.tinyurl.com/y8vxlxp ASIN: B0030MIG24 ) ( Google Books, www.tinyurl.com/2bjjl7s 9780981522616 )
@Rooskies2006 Why would giving up out position be a bad thing? Any hostile aliens would see our signature in EM emissions and atmospheric pollution as soon as they looked at our system... they could readily determine the position of our star from the trajectory of the craft so at least it makes us look more confident.
@lcpltom Thanks for clearing that up, I was aware Voyager launched years after Pioneer but I did not realize (though it makes sense now that you have informed me) they were using separate definitions for leaving the solar system in each claim.
The Deluge occurred in 10800 BC which is a multiple of 3 of the orbital period of planet Nibiru located in our solar system. Thus Nibiru passed by earth at the birth of Christ. It was not a star or nova that the Wise Men were following. In about 20 years, Nibiru will be three quarters around in its orbit of the sun along the minor axis. Why does NASA say that these spacecraft have left this solar system when we have this enormous orbit of 3600 years??
1.)@BNicholson: You show-off son of a B*TCH. None of what you've said has anything to do with the article. And all of your ideas are faggish... and stupid, just like those stupid internet ads.
2.)For the article, no matter how lcpltom explained the different "out-of-the-solar-system" perceptions, the author confused regular PopSci readers by saying "the probes became the first manmade objects ever to plunge beyond the solar system into the inconceivable cold and dark of interstellar space". Does she even work for PopSci? If so, BOO to the editor since not just a few days back, there's an article titled "Voyager 1 Arrives at the Outward Reaches of the Solar Wind, Prepares To Enter Interstellar Space" saying Voyager 1 and not the Pioneer are the first to enter Interstellar Space. Well, if the author is "Astronomy/Science" inclined, she should be aware of the Voyager 1's accomplishments, then she should've said a little bit of something in the article about the difference of the PIONEER and Voyager's accomplishments. Well, the article is okay but long and confusing.
3.) Just a point, if it's true that the factor for the acceleration is a non-machine or non-human error, let's say, the c * H theory, haven't they checked the Voyager 1? What happens in PIONEER should have the same effect to Voyager 1. If it doesn't match, PIONEER Anomaly is 80%-95% human/error
Wow... this is a featured article. How great is the editor not to review the article. Thanks to the people who comment for clearing the confusion on Voyager 1 and Pioneer 10/11 on the first to leave or home solar system.
Damn! Burned you editor.
For the acceleration of the universe, I get that it is Newton's gravitational constant G times the mass of the universe divided by the radius squared of the universe. The mass divided by the radius is linear mass. And linear mass times the gravitational constant is the speed of light squared. So the acceleration is the speed of light squared divided by the radius of the universe is the acceleration equal to 8.98x10^-10 m/s2. However, there is Einstein's excess radius equation which says that objects are 1/3 larger due to relativity, so this acceleration has to be divided by 4/3 or multiplied by .75 to give 6.74x10^-10 m/s2. It will be interesting to see what lower value they determine.
do the voyager 1 and 2 spacecraft exhibit similar anomalies?
Spare us the pseudo-scientific bullshceiße about Nibiru. Go drop hits of acid and communicate with Marduk on an astral plane until your fantasy world ends in 2012. There is no place for such quackery on PopSci.
As far as I understand it, Voyagers I and II have a three-axis stabilization system that has made it somewhat difficult to calculate their respective theoretical positions; a large enough degree of uncertainty that it has obfuscated the observance of similar deceleration. Pioneers 10 and 11 are spin-stabilized and thus, much easier to investigate.
You do realize that Queen Innana came back to earth in 1998 to retrieve the Anunnaki artifacts? Then Lord Anu came through in 1999 upon leaving this solar system in his mothership piloted by the Piol Mantis that EN.KI created. If not, you are not ready to move into the universe.