[hugh_]

You're correct -- the orbital speed and path tell you nothing about the mass. A grain of dust will follow exactly the same orbital path as, say, Jupiter.

It's the redshift/blueshift of the actual star that you need to measure.

[bioweek]

Oh so when the planet is between us and its star, it pulls the star towards us which blueshifts the light?

That sounds hard to detect.

[fh]

> That sounds hard to detect.

Well, obviously you need really precise spectrometers, but just because the effect is tiny, doesn't mean that you can't detect it.