I know there are countless globe planets.
From where does that knowledge come? And how high a number do you consider to be "countless"?
Setting aside the "countless" part, we are at least able to
point to the Wiki, which acknowledges that the planets are round when they answer (without challenging the premise) the question "If the planets are round, why isn't the earth?" The wiki gives the reply stated by Woody.
We can also observe gibbous phases of both Mercury and Venus using ground-based telescopes, which suggests that at least those two objects are round.
The only celestial body close with a large enough angular diameter to discern a surface is the Moon, and it, curiously, only ever presents one side. Coincidence?
One side, with quite distinct curvature at the terminator, suggesting that it too is round. Additionally, while the moon does present the same face to earth all the time, it isn't static. There is a slight wobble,
called libration, which is also indicative of roundness not flatness. I say it indicates roundness because lunar features at the
apparent 'edge' come in and out of view, which would not be the case for a disc with a
true edge. I remembered something posted to another thread which is relevant here:
The moon isn't always pointing perfectly at earth. It librates throughout its orbit, as shown here:
