Re: Pioneer anomaly
- From: Gerard Westendorp <westy31@xxxxxxxxx>
- Date: Sat, 1 Oct 2005 23:23:31 +0000 (UTC)
Esa A E Peuha wrote: [..]
Yes, but note it's not enough to know just the overall charge density; positive and negative charges don't cancel out here. If you have fully ionized hydrogen plasma (that is, free electrons and free protons), the effect on radiation would be immense even if the net charge density is zero.
With the "c" in my dispersion equation for electromagnetic waves, I did not mean net charge density. All that matters is that there are particles that will move in response to electric fields, partially neutralizing them. (This was not so clear from my post, but I did not want to do extensive calculations). So "c" is the charge of a typical particel in the medium, another particle might have charge (-c).
So yes, even a a plasma with no net charge will disperse electromagnetic waves. But the effect is only "immense" if the density is large.
[..]
I'm not convinced that we can get any deceleration on the Pioneer this way. If the charge density is uniform al around the Pioneer, there's no deceleration, so all of the charge would have to be in front of it and none behind it. But that would only be possible if the charge was in a long thin cloud along the Pioneer's trajectory, so that it picks up all of it as it moves along. That's not very likely.
I did not mean to propose that the pioneer is being repelled by a net electric charge. I am saying that if the Pioneer had an electric charge, then it would influence particles around it more strongly than it would through mere mechanical collisions. Even neutral particles will be deflected by an electric charge if they are polarizable. Maybe you have tried electrostatically charging a balloon with your hair. The balloon will bend a thin flow of water from the tap, because the water gets polarized and then gets attracted to the charge.
My main point is really that when considering effective friction, you may need to consider an "effective" frontal area of the Pioneer that is bigger than its mechanical size.
Gerard
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