Yes, because they formed out of a single, spinning disk of gas and dust.

Our solar system is believed to be about four and a half billion years old. It’s thought to have formed from an amorphous cloud of gas and dust in space. The original cloud was spinning – and this spin caused it to flatten out into a disk shape. The sun and planets are believed to have formed out of this disk – which is why, today, the planets still orbit in a single plane around the sun.

It’s one of the wonders of nature that our universe is populated with many sorts of disk-like structures. Our solar system is one of them – and so is our Milky Way galaxy. And you find disks in many other places – for example, the rings of Saturn and other planetary systems – and, it’s believed, in double-star systems, where the substance of one star is pouring onto its neighbor. Before it hits this other star, the material forms a disk.