I'm new to physics, and it's a lot to take in- but there is a problem that I really can't seem to wrap my head around- finding the mass of an orbiting body, like an asteroid. I've looked around a lot and it seems to be impossible to find the mass of an object without going there and orbiting it, but why? If you can know the mass of the object that you're orbiting (for example the sun), can't you use that to discern the mass of the orbiting object (an asteroid)?
Then I thought of the formula F = ma, whereby you can find force with mass and acceleration. This is confusing to me, couldn't you rearrange it as M = F/a, and then find force and acceleration?
So really this is a two-pronged question: Can you find the mass of an object based on that of the one it is orbiting, or could you find it with force and acceleration?
I'm probably missing something big aren't I...
Edit: Thank you for the responses so far! I found a formula recently that purports to be able to find mass with only radius and velocity;
$M = L/rv$
where r= radius v= velocity M= mass L= angular momentum
To find angular momentum $L = Iw$
where I= moment of inertia (v/r) w= angular velocity (rv)/r^2
So it's a little complicated, but does it even work? I tried it on the mass of Venus, and I got it very, very wrong.