Question, given the sun's wobble would result from rotating around the solar system's center of gravity, how feasible is it to actually know with certainty what the solar system is made up of?
Composition analysis is usually done using spectroscopy, which looks for the characteristic wavelengths of compounds that show up when analyzing spectra.
I was answering your question in a roundabout way: usually "wobble" gives very little information about the chemical composition of an exoplanet (other than maybe that it's a large gas giant).
I see. I actually thought your comment might have been said in bad faith as an insult, but I now think it was focused on the context of the post, while mines was focused on the context of what I was replying to. I was replying to the aforementioned method of detecting planets via dopplar shifts in a star's light... I've always wondered about that--with how much precision can you actually know what is causing the shifts. How many gas giants, smaller planets, etc? For example, I suppose two planets of equal size, orbital plane, and 180 degrees from one another would mute their gravitational effect on their host star.
> For example, I suppose two planets of equal size, orbital plane, and 180 degrees from one another would mute their gravitational effect on their host star.
Such orbits are extremely rare. Any such orbit would be highly unstable, as any perturbation would cause the planet to deviate from its location. (Strictly speaking, there are five points where objects can have an orbit that matches that of another planet. They're called the Lagrangian points, and the only ones that are stable are L4 and L5, 60˚ ahead and behind the planet in its orbit.)
From the wobble you can determine the approximate mass of the planet and how long it takes to orbit it's sun. I suppose you might be able to deduce some things about the shape of its orbit as well.
Knowing what a planet is made of would require some other technique. I think the best you could do from looking at the wobble would be to say things like "planets that orbit stars like this and having a mass of such and such with an orbital period of so many days are likely to be made of the same things that other planets with those characteristics are made of".
On the other hand, we can know pretty easily quite a lot about what it's host star is made of by examining the light it emits.
I suppose two Jupiters on the same orbital plane, 180 degrees from each other, would cancel out? Is it possible for observers to really know we have 4 rocky planets, 4 gas giants, and what their mass is, etc? Or, with what degree of certainty could this be known, and from what distance?
I don't believe you can have 2 planets in the same orbit, and once they're in different orbits they'll take a different amount of time to orbit; so you should be able to get individual measurements.
Edit: Well, as per the simulated stable thread, apparently you can have Trojan etc pairs of planets in the same orbit. Interesting.
There's possible and there's likely to happen in nature. two opposing planets in symmetry you'd have to have symmetric mass all around to cancel the forces out. One side will have the galactic centre on and the other won't might even be enough of a tiny imbalance to disrupt the orbits as you say.
If we can detect wobble, can we detect composition? (If someone observing us was more advanced, if they can detect wobble they can probably deduce composition?)
