Argon

Helium, neon, argon, krypton, xenon and radon are noble gases.

Our atmosphere contains 21% oxygen, which is necessary for us to breathe, 78% nitrogen, and 0.9% argon. The other 0.1% consists of water vapor, carbon dioxide, neon, methane, krypton, helium, xenon, hydrogen, nitrous oxide, carbon monoxide, nitrogen dioxide, sulfur dioxide, and ozone.

Argon is a noble gas.

Mars has a very thin atmosphere made of carbon dioxide, nitrogen, and argon.

Argon and xenon gas can also be used in cold gas thrusters due to their inertness.

This is an ideal application for argon gas, whose inertness gives it a huge safety advantage over more reactive gases.