The Pioneer Anomaly -- a problem with theory of gravity?

[United Technocrats]

The two deep space probes launched in the 1970s ny NASA, Pioneer 10 and Pioneer 11, are not where the known gravity laws predict they should be. The guy in charge, the Principal Investigator John Anderson, proposed in 1969 to use the craft (that were to be used for other purposes anyway) to also test the nature of gravity. We now have the results that could mean something's wrong with the laws of gravity:
http://en.wikipedia.org/wiki/Pioneer_anomaly
http://www.daviddarling.info/encycloped ... omaly.html
...
Some scientists believe the laws of gravity need to be adjusted anyway, to match the observations, instead of introducing the concept of "dark matter" / "dark energy" which would account for most of the known matter in the universe. But let's not go that far. The "down to Earth" (or, more accurately, "down to the Solar System") question could be: are the laws of gravity correct? Do they need tweaking, additional corrections for large distances, or are there even more types of interaction involved, that could be seen only over very large distances?

[Peddieville]

Was the effect of dark matter included? Links weren't exactly clear.

[Buffett and Colbert]

It's probably some insignificant problem, that only physicists with no lives care about.

[Peddieville]

that only physicists with no lives care about.

I think that's all of them.

[JuNii]

fools! that's because there is no "outside the Solar System" watch, the two Pioneer probes will just go into orbit a bit after Pluto!

all those "other Galaxies" that the Hubble seen? Matte Paintings!

[Californian Mod Haters]

Who cares?

Can't we care 'bout Yoager 1 & 2

[Nanatsu no Tsuki]

It's probably some insignificant problem, that only physicists with no lives care about.

Say it with me: Aaaaaaaameeeeeeeen.

[United Technocrats]

Was the effect of dark matter included? Links weren't exactly clear.

Those effects are primarily used to explain observations of large and very distant objects, that is to say, not those in the Solar System.

[Daistallia 2104]

Sounds like it's a combination of several things, surprise, surprise.

[Peddieville]

Was the effect of dark matter included? Links weren't exactly clear.

Those effects are primarily used to explain observations of large and very distant objects, that is to say, not those in the Solar System.

Sorry, I thought they were farther out. Still, could have contributed.

[German Nightmare]

As long as stuff keeps falling down (as annoying as it sometimes can be), instead of going up, up and away, I'm quite content.

[Drachmar]

* observational errors, including measurement and computational errors, in deriving the acceleration.
o Approximation/statistical errors
o Significant errors in computation are not likely since (at current count) 7 independent analyses have shown the effect.[4]
* a real deceleration not accounted for in the current model, such as:
o gravitational forces from unidentified sources such as the Kuiper belt or dark matter. However, an acceleration does not show up in the orbits of the outer planets, so any generic gravitational answer would need to violate the equivalence principle [5] (see modified inertia below).
o drag from the interplanetary medium, including dust, solar wind and cosmic rays. However, the measured densities are too small to cause the effect.
o gas leaks, including helium from the spacecrafts' radioisotope thermoelectric generators (RTGs)
o radiation pressure of sunlight, the spacecraft's radio transmissions, or thermal radiation pressure from the RTGs (See Radioisotope rocket), or asymmetrical radiation of the heat from the spacecraft electronics, reflecting from the back of the spacecraft’s dish-like main antenna, causing a recoil like sunlight striking a solar sail.
+ The pressure of sunlight is too small at this distance, and points into the wrong direction. The same applies to the spacecraft's radio emissions.
+ The others are prime suspects, as presented at the second ISSI meeting in Berne, Feb 2007.
+ A recent presentation at the APS April 2008 meeting suggests that differential heating may account for as much of 1/3 rd of the observed acceleration.[6]
o electromagnetic forces due to an electric charge on the spacecraft
* New physics
o clock acceleration between coordinate or Ephemeris time and International Atomic Time.[7]
o A modification of the law of gravity. The theory MOND (Modified Newtonian Dynamics) proposes that the force of gravity deviates to a very different force law at very low accelerations of order: 10−11 m/s2 from the traditional Newtonian value.[8]
o Modified inertia. MOND can also be interpreted as a modification of inertia, perhaps due to an interaction with vacuum energy and such a trajectory-dependent theory could account for the different accelerations apparently acting on the orbiting planets and the Pioneer craft on their escape trajectories.[9] More recently, a model for modified inertia using Unruh radiation and a Hubble-scale Casimir effect has been proposed to explain the Pioneer anomaly,[10] and a possible test for evidence of modified inertia on Earth has been proposed.[11] It has also been suggested that a modification of inertia can explain the flyby anomaly.[12]

[edit]

Too many variables involved. I would think this is why the anomaly exists. I would say the probes are encountering different gravitational affects from dark matter and/or Kuiper belt objects. I would even suggest asking if they took into account the difference in the clock time on the spacecraft vs. earth time since they would be different due to the spacecraft moving out of the space-time effects of the Sun.

Who knows? It's probably a little of all the above.

[United Technocrats]

Too many variables involved. I would think this is why the anomaly exists. I would say the probes are encountering different gravitational affects from dark matter and/or Kuiper belt objects. I would even suggest asking if they took into account the difference in the clock time on the spacecraft vs. earth time since they would be different due to the spacecraft moving out of the space-time effects of the Sun.
Who knows? It's probably a little of all the above.

Could be, but this would not be the first time anomalous observations were made and much later, a new theory would explain them. With all the checks they've done on the equipment, the problem seems to persist...

[United Technocrats]

that only physicists with no lives care about.

I think that's all of them.

No lives? Well, if I were a cosmologist, I'd love to spend my no-life researching asteroids and stuff with Dr Amy Meinzer... If she looks this good at 35, gosh....

[Peddieville]

No lives? Well, if I were a cosmologist, I'd love to spend my no-life researching asteroids and stuff with Dr Amy Meinzer... If she looks this good at 35, gosh....

My bio teacher told us a story about a famous profesor at her school who had 13 kids, not all by the same women, either. Who says natural selection doesn't exist?

[Drachmar]

Too many variables involved. I would think this is why the anomaly exists. I would say the probes are encountering different gravitational affects from dark matter and/or Kuiper belt objects. I would even suggest asking if they took into account the difference in the clock time on the spacecraft vs. earth time since they would be different due to the spacecraft moving out of the space-time effects of the Sun.
Who knows? It's probably a little of all the above.

Could be, but this would not be the first time anomalous observations were made and much later, a new theory would explain them. With all the checks they've done on the equipment, the problem seems to persist...

clock acceleration between coordinate or Ephemeris time and International Atomic Time.

My bet is that this is the primary cause.

[South Lorenya]

That's a good question...

It's entirely possible that there's a planet or moon something out there they don't know about that's large enough to cause the anomaly.

Sounds odd, right? Well, keep in mind that it happened before -- when Cassini first discovered the moon Iapetus in 1671, for some reason it could be seen on the western side of Saturn but never the eastern side. Did the moon travel through wormholes? Did it turn invisible for half of the orbit? It wasn't until 1705 that Cassini discovered it has a light-colored half and a dark-colored half, and for half the orbit (specifically the eastern half) only the dark side -- which the initial telescopes weren't good enough to see -- was visible!

Bright side
Dark side