# Weird Gravity Messin' With Our Probes **URL:** \ **Category:** Factual Questions\ **Created:** [May 22, 2001, 3:33pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191 "2001-05-22T15:33:24Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![ElDestructo](https://avatars.discourse-cdn.com/v4/letter/e/f0a364/32.png) [@ElDestructo](https://boards.straightdope.com/u/ElDestructo)\ **Post date:** [May 22, 2001, 3:33pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/1 "2001-05-22T15:33:24Z")
I have read from a couple of sources (most recently, CNN) that studies of the trajectories of the Pioneer 10 & 11 probes have revealed that something screwy’s going on with gravity. If my understanding is correct, the probes aren’t going as fast as they should be. All factors have been taken into consideration, and the numbers still don’t work out. At first they thought that Pioneer 10 had discovered a new planet from its gravitational effects, but since they have observed the same efects on the Pioneer 11 probe on the other side of the solar system, they now think there is some new fundamental force of nature involved, or some component of gravity that has not been detectable previously. So, what gives? What are the prevailing theories, if any, about what’s going on out there? Anti-gravity? Quantum foam drag? Alien tractor beams? Sailing off the edge of the flat earth? Or are JPL’s computers buggy? ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [May 22, 2001, 4:26pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/2 "2001-05-22T16:26:20Z")
From NASA’s [Pioneer Home Page](http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PNStat.html): > [@](#): > > ANOMALOUS GRAVITATIONAL FORCE? A discussion of this phenomenon appears in the 4 October 1999 issue of Newsweek magazine (See also the December 1998 issue of Scientific American.) The mystery of the tiny unexplained acceleration towards the sun in the motion of the Pioneer 10, Pioneer 11 and Ulysses spacecraft remains unexplained. A team of planetary scientists and physicists led by John Anderson (Pioneer 10 Principal Investigator for Celestial Mechanics) has identified a tiny unexplained acceleration towards the sun in the motion of the Pioneer 10, Pioneer 11, and Ulysses spacecraft. The anomalous acceleration - about 10 billion times smaller than the acceleration we feel from Earth’s gravitational pull - was identified after detailed analyses of radio data from the spacecraft. A variety of possible causes were considered including: perturbations from the gravitational attraction of planets and smaller bodies in the solar system; radiation pressure, the tiny transfer of momentum when photons impact the spacecraft; general relativity; interactions between the solar wind and the spacecraft; possible corruption to the radio Doppler data; wobbles and other changes in Earth’s rotation; outgassing or thermal radiation from the spacecraft; and the possible influence of non-ordinary or dark matter. After exhausting the list of explanations deemed most plausible, the researchers examined possible modification to the force of gravity as explained by Newton’s law with the sun being the dominant gravitational force. “Clearly, more analysis, observation, and theoretical work are called for,” the researchers concluded. The scientists expect the explanation when found will involve conventional physics. ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [May 22, 2001, 5:36pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/3 "2001-05-22T17:36:45Z")
[Here’s a fellow](http://www.allanstime.com/UnifiedFieldTheory/gravity.htm) who claims to have figured it all out, complete with new gravity equation and everything. (Warning: he is a scientist who believes in God.) Chronos (and any other physicists), could you take a look at it? ---
**Author:** ![MrDeath](https://avatars.discourse-cdn.com/v4/letter/m/22d042/32.png) [@MrDeath](https://boards.straightdope.com/u/MrDeath)\ **Post date:** [May 22, 2001, 10:44pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/4 "2001-05-22T22:44:12Z")
> [@](#): > > \*Originally posted by Libertarian \* > \*\*[Here’s a fellow](http://www.allanstime.com/UnifiedFieldTheory/gravity.htm) who claims to have figured it all out, complete with new gravity equation and everything. (Warning: he is a scientist who believes in God.) > > Chronos (and any other physicists), could you take a look at it? \*\* I’m enough of a physicist to know when I can stop reading. This guy’s a lot subtler than many of the pseudo-scientists that I have run across, but I know that I can stop reading when I see something like: > [@](#): > > Just as a magnetic field requires no particles to make the field, so there is no graviton required to make a gravity field. This is patently false; any sort of force-interaction uses particles to effect the exchange. The particles in a magnetic field are photons. But there’s worse to come. He also says: > [@](#): > > In chemistry and molecular spectroscopy we take for granted the seven electron shells that describe the energy states of electrons in their various atomic and molecular configurations. . . . And he goes on to talk about “seven channels or states of conductivity for the diallel lines” that are ‘connected’ to these seven electron shells. I don’t know where he gets the number seven from. From [this nice site](http://www.madsci.org/posts/archives/mar99/921736624.Ch.r.html), we can see from the given parameters that there are an infinitude of quantum shells that electrons can occupy; this is also demonstrated very nicely in spectroscopy by the emission lines of hydrogen, that form a set of infinite converging sequences. I don’t know what this guy’s after, but he’s as good a BSer as they come. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 23, 2001, 3:53am UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/5 "2001-05-23T03:53:29Z")
Even better clue: When you see right up at the top, “New Unified Field Theory”. When you see something like that on any public webpage, you can rest assured you’re dealing with a crackpot. If this guy had a genuine theory unifying gravity with the other forces, he would be publishing in PhysRev, not on some web page. The fact that he believes in God is irrelevant: A disproportionate number of genuine physicists do. It’s the biologists who have a tendancy towards atheism. As for the anomolous force on the Pioneers, last I heard, the prevailing explanation was just that we had slightly misestimated the effect of drag from the interplanetary medium. Frictional forces of any sort are very difficult to accurately model, and we’re talking about a very small discrepancy, here. ---
**Author:** ![Phobos](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@Phobos](https://boards.straightdope.com/u/Phobos)\ **Post date:** [May 23, 2001, 12:33pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/6 "2001-05-23T12:33:50Z")
> [@](#): > > \*Originally posted by Chronos \* > \*\*As for the anomolous force on the Pioneers, last I heard, the prevailing explanation was just that we had slightly misestimated the effect of drag from the interplanetary medium. Frictional forces of any sort are very difficult to accurately model, and we’re talking about a very small discrepancy, here. \*\* Much more likely that the “weird gravity” idea. Anyway, it’s not known what’s going on and the media is just jumping on the more flashy headline. An article about weird gravity appeals to more people than mundane frictional forces. Just wait until Fox TV gets a hold of this! :rolleyes: ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [May 23, 2001, 1:17pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/7 "2001-05-23T13:17:28Z")
Thanks, everyone, for your time and trouble. One comment raised a new question set for me: > [@](#): > > As for the anomolous force on the Pioneers, last I heard, the prevailing explanation was just that we had slightly misestimated the effect of drag from the interplanetary medium. What effect, if any, does the interplanetary medium have on planetary and moon orbits and revolutions, and things like asteroids and planetary rings? Given the quantitative difference between the presumed effect and the actual effect on Pioneer, how does this difference bear on calculations of momentum of bodies in the solar system that have, or will have, over time and in the course of their movements, travelled considerably further than Pioneer? Also, is electromagnetism in general effected by this medium; that is, does it interfere with our astronomical observations of deep space? ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [May 23, 2001, 3:07pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/8 "2001-05-23T15:07:23Z")
I figure the Pioneers are encountering the Heliopause, the boundary there the sun’s solar wind can no longer expand against the prevailing interstellar conditions…the probes’ tail wind just became a head wind. ---
**Author:** ![bernse](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bernse](https://boards.straightdope.com/u/bernse)\ **Post date:** [May 23, 2001, 3:20pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/9 "2001-05-23T15:20:35Z")
Encountering the Heliopause is what I thought of too, but, I then I was thinking Ulysses is nowhere near that far away, is it? ---
**Author:** ![Sofa\_King](https://avatars.discourse-cdn.com/v4/letter/s/58956e/32.png) [@Sofa\_King](https://boards.straightdope.com/u/Sofa_King)\ **Post date:** [May 23, 2001, 3:34pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/10 "2001-05-23T15:34:17Z")
And while **Libertarian** is at it, couldn’t the discrepancy simply be a mis-estimation of the mass of the Kuiper Belt and/or the Oort Cloud? ---
**Author:** ![ElDestructo](https://avatars.discourse-cdn.com/v4/letter/e/f0a364/32.png) [@ElDestructo](https://boards.straightdope.com/u/ElDestructo)\ **Post date:** [May 23, 2001, 7:39pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/11 "2001-05-23T19:39:11Z")
It seems like we should have a pretty good estimate of the mass of the Kupier belt and Oort cloud from our observations of the orbits of the outer planets. Besides, the quote above from JPL claims that the gravitational effects of small bodies in the solar system have been ruled out. Also, what about the Voyagers? Are they exhibiting any anomalous acceleration? ---
**Author:** ![Phobos](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@Phobos](https://boards.straightdope.com/u/Phobos)\ **Post date:** [May 24, 2001, 12:14pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/12 "2001-05-24T12:14:43Z")
[Status of Ulysses, Voyagers, and others](http://spacelink.msfc.nasa.gov/NASA.News/Where.Are.They.Now/.index.html) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 24, 2001, 9:51pm UTC](https://boards.straightdope.com/t/weird-gravity-messin-with-our-probes/66191/13 "2001-05-24T21:51:38Z")
IPM drag would and does indeed have an effect on other celestial bodies, but you’ve got a square-cube effect going on here: Gaseous drag forces are (roughly) proportional to the area of an object, while mass scales as the volume of an object. Plug this into F=ma, and you see that for two objects with the same density and shape, acceleration from drag will be inversely proportional to size. To see the effects, you need to precisely measure the orbit of a small object, which pretty much leaves us with artificial probes. Whatever we’re seeing, it’s probably not a gravitational effect, since gravity (so far as we know) effects large and small bodies in the same way, and we’re not seeing this, whatever it is, happening to the larger solar system bodies. The IPM does interact with the solar and planetary magnetic fields, but it has negligible effect on optical observations, mostly because the solar system is so small. Looking through a few billion lightyears of intergalactic medium has a lot more effect on light than a fraction of a lightyear of interplanetary medium.