Mars

Mars, named after the Roman god of war, is the fourth planet from the sun.

Background
Before the Great War, the United States Space Administration planned to launch a manned mission to Mars by July of 2078, which was called the Mars Shot Project. However, the project was delayed by a year due to unrest overseas. By 2077, the public had little interest in men going to Mars, and so the USSA attempted to garner support by investing in the popular television show, Captain Cosmos. In the end, it would all be for nought, and the project would never be carried out due to the nuclear war of 2077.

At the Museum of Technology, a list of space facts mentions that a volcano on the planet, Olympus Mons, is the tallest known mountain in the solar system, three times the height of Mount Everest.

In issue #6 of Grognak the Barbarian, the titular character faces off against Maula, the war maiden of Mars.

On Mothership Zeta, one of the abducted humans asked if a device on the ship was a Martian sex machine.

At the Bloomfield Space Center, the Hermes-13 was designed for a mission to Mars, before being repurposed to carry a power reactor to an orbital nuclear missile platform.

The Vault Dweller can claim to be from the planet, asking Jason Zimmerman if he would like to see their firelance.

Appearances
Mars is mentioned in Fallout, Fallout 3 and its add-on Mothership Zeta, Fallout 4 and its Creation Club content Captain Cosmos, and Fallout 76, and would have been mentioned in Black Isle Studios' cancelled Fallout 3.