The Pioneer Anomaly

Two slowing probes baffling scientists

It seems that Pioneer 10 and Pioneer 11, which are 86 and 57 AUs from the sun, respectively, are traveling more slowly than expected.

(An AU is an “astronomical unit”, the distance from our sun to our planet. Therefore, Pioneer 10 is 86 times as far from the sun as the Earth is. You may think it’s a long way down the road to the chemist, but that’s peanuts to this.)

They call this phenomena ‘the Pioneer Anomaly’ and they don’t know if it’s due to leaking propellant, some heretofore-unknown physics, or if maybe it’s just Bush’s fault.


However, a nearly eight-year study of those possible causes amounted to “no smoking gun,’ said Slava Turyshev, one of the researchers on that study and the ESA proposal from JPL.

Scientists also have looked into “just about everything we can think of,’ Nieto said.

What really puzzles scientists, Turyshev said, is that the anomaly is constant with respect to time and distance from about 1 1/2 billion miles away from the sun to about 6 1/2 billion miles out. The anomalous behavior has been observed in other deep space vehicles such as Voyager and Ullyses.

Nieto said interest in determining the root of the Pioneer problem “is growing in the ether.’

Here are some additional theories from MO, in no particular order (other than they start out bad and get worse):

  • Increased magnetic activity on Earth is affecting the probes’ velocity
  • They’re just plain tired
  • They are nearing the edge of the turtle that holds up everything on his back
  • This is actually the way George Lucas intended them to fly all along, but the technology just wasn’t available back then
  • NASA engineers forgot to unhook the giant bungee cord that connected the probes to the launch pads
  • Uranus sucks
  • Reduced NASA funding is hurting mileage
  • Dan Rather: “This is the same speed they’ve always been traveling”
  • It’s gotta be the shoes
  • In Space, No One Can Hear You Lose Steam

For info on the current stats of the Pioneer and Voyager probes, check out Heavens Above’s ‘Spacecraft escaping the Solar System’ page. (hat tip to Fred)


  1. As I read a recent article on the Pioneer probe anomalies, I had a few alternative ideas that were not already listed. They are very simple, but have a fairly high probability. I would send these to Slava Turyshev directly, but I don’t have his contact information. I’d like to pass these (serious) proposals on to him … thank you. Proposal #1: NASA has, inadvertantly, created two artificial comets. The flight path of the probes was such to send them around the sun, out into the outer reaches of the solar system, and then bring them back in due course of time. Think of it like the proverbial cannonball. It goes straight forward and up for a while, but then it starts to curve and finally comes back to the Earth. Like leaving the confines of Earth’s gravitational well from the ground or leaving orbit, more energy is needed to escape the atmospheric than to put an object into orbit. While the Pioneer crafts were designed to explore the planets and other celestial bodies, it was sent in a huge arching projection. This arch was insufficient to give it the needed velocity to leave the solar system. A straighter path or more propulsion would’ve allowed it to escape the confines of these planets and asteroids, but such was not the case. If they’re still in working order, we may be able to get a 2nd pass of planetary data as they come back to roost. If we play our cards right, we might even be able to perform some kind of intercept like what was planned for the solar capsule when it comes back by … in another 30 years. On the other hand, the return may increase its velocity to the point that it can finally be released: from the original tight spiral around the center to the eventual fast, loose projection. Proposal #2: Since the Pioneer craft were launched, an idea has been put forth concerning the existance of the numerous Kuiper’s Belt objects and the possibility of a encapsulating region of cosmic dust known as the Oort Dust Cloud. Perhaps the accelerated slowing is due to increased drag on the crafts from more concentrated areas of this dust. Gravity still works the same, but the dust is hitting against the craft causing it to slow faster than expected which allows gravity to act on it differently. The dust likely wouldn’t be large enough to be realized unless you were there or were getting active telemetry back. This is similar to the effects of air resistance on objects, esp. those moving at higher speeds, which has given rise to the science of aerodynamics to help objects like cars to move through the air at higher speeds with less resistance and greater efficiency. Proposal #3: What is our current location in our own orbit in relation to the Pioneer craft? It may be possible that the craft themselves haven’t moved, but our own selves. We move in 3 dimensions in relationship to the craft. Any microwave source would need to be originated FROM earth so our own cellestial location is a factor in the Doppler Shift. Even as a moving car from a stationary noise is equally responsible as a moving sound from a stationary location. When both the origin and the listener are moving, all manner of anomalies could turn up. None of these require a ‘gravitational bogey man’ in the form of dark matter, convoluted and unpredicted theories of gravity, or alternate dimensions. Thank you for your time and attention, Tesla Falcon

  2. I, too, had a hypothesis, but it is related to two other ‘odd’ experiments. Spin a superconductor fast enough, and a 2% weight reduction of objects suspended above it was observed. Last I heard the scientist stopped working at her lab and retired ‘to pursue commercial opportunities’. Combined with: The shape of the equations dealing with Einstein’s relativity imply that the electomagnetic force has no effect on the gavitic force. However, very recently some smart mathematician reformulated the equations, reversing the variables for time and space. According to physicists this won’t make any difference to the effect of the equations, but it does change the way they look. The newly reformulated equations seem to imply that strong magnetic fields can dampen the effects of gravitic fields. So, those two ideas together seem to support eachother. Spinning superconductors produce strong magnetic fields; magnetic fields flatten gravity; The sun’s magnetic field flattens the sun’s gravitic field, making large-scale predictions inaccurate, as the pioneer anomoly seems to be showing. My problem? Wouldn’t a flatter gravitic field imply a *faster* rate of travel, not slower? The pioneer craft should be farther away, not closer, than they were predicted to be by now… –John Hentges’ 2cents