Mars was the inhabited fourth planet of the Sol system, in the Alpha Quadrant.

The planet was a dusty, cold, desert world with a very thin atmosphere. The Martian colonies were established in 2103. It was the first planet to be terraformed by Humans. Colonists originally dwelt within domed cities while the verteron array was used to redirect comets and asteroids towards the Red Planet to impact in the polar caps. This freed carbon dioxide and released it into the atmosphere, increasing the planet's temperature and water volume. By 2155, conditions in the lowlands of the Martian surface were sufficiently altered to allow Humans to roam freely without heavy environmental suits, though one would still have to dress warmly for the near-arctic surface temperatures.

Mars was one of humanity's oldest colony worlds and the location of Utopia Planitia Fleet Yards, a massive Starfleet shipbuilding facility. Many of the Federation's most famous starships were built here.

In 2385, the planet was attacked by rogue synths, who destroyed the Utopia Planitia shipyards and bombarded Mars so heavily that they ignited flammable vapors in its stratosphere. As of 2399, the planet's atmosphere was still burning, rendering the planet uninhabitable.