i understand that there are 2 main ways to observe and determine properties of exoplanets but my question relates to the method which involves measuring the "wobble" caused by the gravitational influence of a planet on it's parent star. is the measurement always based on the assumption that only one planet is present in the solar system in question and would the presence of other, as yet unobserved planets affect conclusions drawn about the mass and orbital distance of the planet. would the presence of other orbiting planets cancel out the "wobble" or accentuate it?  

If I was to take a huge heat-proof tube and stick it through the very centre of the earth and then jumped down it, what would happen when I reached the middle? Would I float at the very centre?

What caused this tree resin, emerging where a branch was sawn off, to flow out at an angle, then vertically downwards, before flowing in an upward curve (see photo)?

Rupert Ward, Albany, Western Australia