Wobble in the Goldylocks Zone

Last week I talked a little about why I thought the new planet in the Goldylocks zone around Gliese 581 had a pretty high bogus factor. Since then I have been trying to rationalize it and came up with this figure. It shows the basic method for deconvolving a signal to resolve the wobble due to a planet. The dark blue line is something like what they would measure - in this case it is the sum of the other lines, each of which is the component of motion that each individual planet would apply on the star. The blue line shows that the star is moved as much as a few thousand meters several times a year as the planets circling it tug it around and also that the planets which circle it with different periods tend to cause perterbations in the star's motions. 

By modeling the effect of various mass planets at different distances (and thus periods), scientists can strip away the modeled value and use the residuals to calculate the size of the next smallest planet. I made the largest planet the red line, which has the most influence on the star. Much like Jupiter here in our solar system, it dominates the star's motion and likewise, small errors in the red line are probably just as significant as the total influence of smaller planets (like that grey line). 

The blue line actually includes the influence of 7 planets here, but the fact is that after I plotted the third planet, you couldn't even see the influence of any of the smaller planets. The Goldylocks planet Gliese 581g pulls at Gliese as much as 1 m, which is durn close to the precision of the technique they are using to measure relative velocity. Also note, that in this little model I have here, the largest influence moves the star by as much as 10,000. That means that the technique, including the modelling component, needs to be accurate and precise to one part in 10,000. While this level of accuracy is not unheard of, especially in the physics world, it would not surprise me if the planet is discovered to be a rounding error sometime in the next decade.