What is so special about the Ultima Thule passed by New Horizon spacecraft? I read that the New Horizon spacecraft passed by the Ultima Thule. I also got to know that it is a flat, snowman-shaped rock.

What is so special about it?
Ultima Thule is the first small Kuiper Belt Object (KBO) we have visited. For the first time, we can see a KBO as more than a tiny point of light in a telescope.
it seems to be flat, rather than roughly round. This is really unusual (we've never seen that shape before in planets, moons, asteroids etc.).