Re: Solar System around 55 Cancri

On Fri, 9 Nov 2007, Rumpelstiltskin wrote:

On Fri, 09 Nov 2007 13:23:36 GMT, Rumpelstiltskin
<PleaseDoNotReplyByEmail@xxxxxxxxxxx> wrote:

<snip>

We can tell the mass of the planets from the mass of the star,


That should have been "We can tell the mass of the planets from the mass of the star and the amount of wobble,"

In fact, there is uncertainty because we don't know the angle of the systems with respect to us. We can't yet see the star move from side-to-side, burt we can detect doppler shifts in the star due to variations in motion toward or away from us. Therefore the mass of the planets is an approximation based on an assumption that we're seeing the systems edge-on, which only gives us a minimum mass for any planets. If a planetary system was face-on with regard to us, we wouldn't see any doppler shift in the star at all so we wouldn't know there was a planetary system there. Given a large enough sample, we can assume that on average we would see the systems at a 45 degree angle which would mean we'd underestimated the size of the planets by about 30%, but since we can't see shifts in face-on systems at all, those systems are excluded from the sample, so our average is a little better than that.

There are, I think, a couple of cases with small stars and huge planets where we actually can "see" the planet, in the sense that if we can add up a lot of observations, then the planet will show up. I think police surveillance can produce better pictures of criminals on low-resolution videos than can be seen from any one single frame, by adding up the face of the criminal in a lot of individual frames, in the same way.

I agree. I seen more stuff on this in the news. Looks like they have been measuring the wobble for many years-- as much as 10. This with the doppler shift data-- although I don't remember hearing about that-- would give them a pretty precise idea of the planets esp if we were looking on the sun from the north or south poles.
.

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