Newly Discovered Alien Planet as Dense as Lead

reply to post by MrInquisitive

Addendum to my last post

Looking into the issue further, I realize one must calculate the radial velocity of the star, too, which does still involve Doppler effect calculations, and then the planet's mass is determined from the relationship between the two bodies' momenta. However, the Doppler effect issue CaptChaos mentions -- I believe -- has to do with measurements for very distant objects, i.e. in different galaxies. Hence, the Doppler effect for not-too-distant stars ought to work according to the theoretical model.

Even so, I admit that the whole business gets a whole lot more complicated when dealing with solar systems with multiple planets; in such cases one would work on figuring out the mass and orbit of the largest planet first and work one's way down to the smaller ones while correct for the effects of the larger ones. In any case these are ballpark estimates, not rigorous absolute values, but they are good enough to give a reasonable approximation to reality. So yes, there's a little arm waving involved, but one can get a decent estimate.