Mystery Force Affecting Probes

imipak writes: "The BBC reports that after exchaustive investigations, NASA scientists have run out of possible explanations for the mysterious tiny course deflections experienced by the Pioneer and Voyager spacecraft as they head out of the solar system towards the heliopause. Could it be that there's something wrong with our theory of gravity? (Well, yes, we already know that...) or could it be Oort Cloud objects? The tenth planet? Informed comment, please!"

Comments

Informed Comment

[Anonymous Coward]

So, let me get this straight. NASA has given up trying to explain this, they have no idea. So for informed comments, now we turn to ...

Slashdot Readers

Hurrah! Please explain it for me, guys. I have a friend at NASA who would really like to know.

Re:Informed Comment

[Paul Komarek]

As someone considering NASA after their Ph.D., I find your comment offensive and ill-informed. Government wages for scientists at NASA are decent, easily enough for comfortable living. But there is also job security, an above-average vacation policy (for the USA), and exposure to a wonderful variety of people and technologies.

Not to mention that some people might actually like helping their country, despite the fact that folks like you diss all public servants as "also-rans". Because US taxpayers have a screwed-up sense of what public servants deserve, there are some fairly draconian policies in place in various government institutions:
* All cups of coffee must be accounted for, and paid for individually
* No Christmas parties, even if financed by
discretionary money
* Spouses not allowed to ride in government
vehicles, even when travelling together
Obviously, I don't like your attitude. That said, it's quite possible you were making a joke -- an inappropriate joke, in my opinion. How would you like it if your company couldn't hold a Christmas party, despite a year of record performance?

Your comment is certainly not "informed". Consider the following data, all found via Google at
http://www.hq.nasa.gov/office/HR-Education/workfor ce/endofy99.html:
* 74% of NASA's workforce have a Bachelor's
degree or higher.
* 34% have a Master's or higher
* 10% have a Doctorate
For an agency with 17,000 employees, that's not bad. How does your company stack up, Mr. Fancy Pants? Here's some more info:
* Average salary across all NASA's scientific
and engineering employees: $79,000
* Average salary across all NASA's employees,
regardless of job: $69,000
* Average salary of scientist or engineer at
NASA's headquarters: $103,000
* Average for same at Ames Research Center:
$86,000
* At all of NASA's centers, scientists and
engineers have higer average earnings than
professional administrators -- music to my
ears!
Remember that these are averages, not maximum salaries. Also, consider that NASA has 17,000 employees, though I don't know how many are scientists or engineers. Given that 35% percent have an advanced degree, this is likely to be a large number. At any rate, these numbers are just fine, if you're not a mercenary.

It is very interesting to look at the top ten reasons people remain federal employees. You can see this list here.

-Paul Komarek

Re:Informed Comment

[slickwillie]

I'm sure it's cognitive gravity. You know, like when Wile E. Coyote runs off the cliff, but he doesn't fall until he looks down and realizes he not standing on solid ground anymore. I think those NASA guys stopped looking at those spacecraft, and they stopped moving until someone looked again.

Re:Informed Comment

[selectspec]

Bill Gates dark life force is clearly sucking the energy out of these scientific projects. We must remember that these spacecraft have been an endevour of science and that the scientific process has often been linked as an inspiration for Open Source. Need to paint a picture people? Of course, the Gates-Effect doesnt bother the planets. I'm still trying to figure out the Intel angle, but I suspect they might be involved too.

Re:Could this be the "missing mass" explanation?

[Christopher Thomas]

If they're slowing as they get very far from the Sun, that seems to imply that the force of gravity is not dropping of quite as fast as 1/r^2.

The problem is, as the article points out, we would have seen the effects of this on the orbits of the planets if this was the case.

I'm personally wondering about drift in the probes' radio sources throwing off the doppler measurements, but if this was happening they should have caught it already (you can directly measure the probes' positions by measuring the round-trip signal times to them at a few different imes during the year).

Re:The Paper is here

[nyet]

My (recently deceased) dad is on that paper.. he believed that it was most probably (b) (outgassing of some sort, possibly a malfunction/weakness common to both pioneer probes). No real evidence of that of course, and a "mysterious" force is more publishable ;) Still it is very spooky.

(g) and (h) were (in his opinion) the least likely.

Note that the paper was actually first released in April, and just revised today.

Stellar gas?

[KFury]

Could it be that there's just more mass in the solar system than we think? Wait, hear me out. I'm not talking about Planet X or a bloated G, I'm talking about ambient stellar gas.

Here's the deal: On the Earth, the gravitatinal forces acting on you at the surface all sum out to equal to the forces that would be exerted by a point source with the Earth's mass and a distance r, the diameter of the Earth. Though that ocean to your left and that continent to your right pull you in opposite directions, and the ground under your feet is pulling harder than the ground in China (um, unless you're in China, in which case, 'hi'), but it all sums out exactly right to a point mass at radius r.

Now, take that example and pose it to the solar system. Forget about the forc of solar wind blowing, and realize that all that wind has mass, and exists everywhere. It's pretty thin, but it's a lot thicker than the four hydrogen atoms per cubic meter in deep interstellar space. All that stuff, wispy as it is, has mass, and even though most of it is so godawful far away, the net gravitational effect of all of it is as if there were an additional point source inside the sun, with the mass of all the stray gasses and particles inside the huge sphere that has the sun as the center and the space probe on the outer surface.

What makes the math even more wonky is that, assuming a roughly even distribution of gas as inversely proportional (or inverse square, or even constant, doesn't matter in this case as long as it's uniform by uniform radius) to the distance form the sun, then the farther out the probe goes, the more mass there is behind it, and the farther back the point source goes.

If the density were uniform (it's not) then the effect of this force would actually increase as the probe got further away. As it is, it may be a constant force. For conceptualization's sake, if you had a well to the center of the earth and went to the bottom (forget magma, use the moon if it makes you feel better) you'd be weightless. Go halfway up, and you'd have a force of one-half g. Go to the surface and you are being pulled with a stronger force than you were when you were closer to the center.

Anyhow, HTML's bad for math, but I just wanted to get the idea out there. I don't have enough info on particulate density over the scope of the solar system and beyond to make any educated numbers anyhow. Hopefully someone out there does.

Kevin Fox
--

An Explanation

[Mignon]

I have found a truly marvelous explanation, which this input field is too small to contain.

--Fermat

Re:Shape of the universe

[coyote-san]

The only problem with this analogy is that the precession of Mercury's perihelion occured in the area of the highest graviational field within 4 light years. This is where you would expect to find simplier theories to break down.

In contrast, the probes are in areas with a relatively small gravitational field. While the field is smaller than anything this side of Pluto's orbit, it's not that much smaller. (The contribution from the sun is lower, but the contribution from the entire Milky Way, and our gravitationally bound galactic cluster, is just as large.) A breakdown in the existing theory just doesn't make sense here - and even if it does break down, where does the energy come from?

As for the issue of the space of the universe... get a grip. :-) The shape of galaxies - and interactions of galaxies in clusters and super-clusters, shows that the universe is "flat" on the scale of many millions of light years. If you equate that to the size of the earth, then 1 meter represents about 1 LY, and the helipause will easily fit within a postage stamp. Or maybe the period at the end of this line. Something definitely "flat" by any reasonable definition.

does gravity push and not pull?

[thogard]

An early theory of gravity said it pushed in all directions at the same time but things with mass blocked it slightly. The attraction force is simply the delta of pushes from two sides not being equal. This was thrown out because things in space would slow down over time. However...
it appears that things do slow down over time. The deep space probes are not the only ones showing this. The gps sats are doing it and this is one of the problmes that gravity probe B is suppoed to help solve. I guess it means we have a wrong view of what keeps up stuck on this world.

Re:Just shows how much more there is than we know

[SIGFPE]

Let us spread this failing of science everywhere, so that we can regain our childhood sense of wonder and expose the necessary failing of science.

A failure to explain a phenomenon isn't a failure of science. It's the opposite. It's what every scientist dreams of. Finding a disagreement between observed reality and theory is what the most exciting science is about.

I'm not sure what planet you're on because you seem to be trying to write an anti-science diatribe and yet much of what you say is no different from the view of a scientist.

--

assumptions about gravity

[Argylengineotis]

There is no reason to suppose gravity gradients are even across large distances (>20 A.U.) If you pour over your references, you'll see that at no point, from the General Theory on up, does any theorist take into account the possibility that between strong influences (astral bodies), spacetime must be smooth. in fact, it is perfectly reasonable to suppose that there are variations large enough to account for these variances in trajectory. The universe is not beholden to your 'rubber sheets and marbles' analogy for gravity.

The Paper is here

[efuseekay]

Check out the JPL final paper on this.

Possibles are :
(a) Heat Ejection (b) Gas Leak (c) Clock Drift (d) Anomalous objects (pretty dead, despite BBC giving prominence) (e) modifications to gravity (f) solar radiation pressure (g) systematics of observations (h) antenna radiation pressure

Let the armchair speculation begin. (But remember to read the paper to check your answers!) Have Fun!

Re:The Paper is here

[imipak]

Right. Thans for the link.

Sod's law suggests that it's 99% likely to be one of (a|b|c|d|g|h). However, astronomers and physicists are generally rather good at methodically excluding likely explanations, starting with the least unlikely, until all that's left, however unlikely,..

We know that, at some level, the standard model is inconsistent - quantum physics and relativity are mutually incompatible. One tantalising observation for which there's no generally accepted explanation is that gravity is many, many orders of magnitude less powerful than the other fundamental forces.

I'd love ot believe that this phenomena, which has been bobbing around for a few years now, is a pointer to some Theory of Everything. But, after 25 years in space, the tiniest force acting on the probes which is not accounted for, can stack up to an observable difference of position from prediction.
--

Shape of the universe

[rmcgehee]

A hundred years ago, an unexplained force seemed to be affecting the orbit of Mercury, causing a wobble in its orbit that should not have existed in a Newtonian framework. Then in 1915, Albert Einstein developed the theory of General Relativity, describing the complex curvatures of our universe that could explain Mercury's path around the Sun.

While this news report is very likely just a measurement error, we must be reminded that the last time we discovered an error in a celestial body's trajectory we reinvented the notion of the universe.

One of the big open questions of the day is: What is the shape of the universe? Euclidean, hyperbolic, a torus--we aren't sure. It is thought that each of these geometries would profoundly affect an object moving across the universe in a different way. These NASA probes could in a sense be the moving laboratory that we need to understand what exactly our universe looks like.

Robert

http://wso.williams.edu/~rmcgehee