Here's why:

* Our Solar System: Mars is a planet within our Solar System.

* Solar System Location: Our Solar System is located within one of the spiral arms of the Milky Way galaxy, called the Orion Arm.

* Milky Way: The Milky Way is a vast collection of billions of stars, planets, gas, and dust, held together by gravity.

So, Mars, along with Earth and all the other planets in our solar system, are part of the Milky Way galaxy.