There is a misconception that there are planets with absolutely *no* atmosphere. All planets in our solar system have at least a very thin exosphere, which is a very, very faint atmosphere.

However, there are two planets in our solar system with extremely thin atmospheres, so thin that they are often considered to have practically no atmosphere:

* Mercury: Mercury has a very thin exosphere, composed mostly of sodium, potassium, and hydrogen.

* The Moon: The Moon has an extremely thin exosphere, composed mainly of helium, neon, and argon.

It's important to note that even though these planets have very thin atmospheres, they are not completely devoid of them.