Mars

Mars is the fourth planet in the Sol System, the first world in the system to birth sapient life, and the site of a demonic invasion which rendered the planet uninhabitable.

Overview
Mars is the fourth planet in the Sol System, a terrestrial planet that was rendered uninhabitable for several million years. While habitable, it was known to be very Earth-like, although its gravity was notably lighter. Once rendered uninhabitable, its gravity became much lower, and its atmosphere became inhospitable.

Geography
Mars was once mostly hospitable landmasses, with seas and lakes as its surface water, and ice caps at its poles. A wide variety of natural landscapes encompassed Mars, varying depending on the climate and area, with a large number of hills and highlands to its south with flat plains at its north. After the demonic invasion, Mars' geography was greatly rearranged. It kept the plains at its north and the highlands at its south, and its ice caps, but was now devoid of liquid water, and the rest of its surface became dominated by red sands rich in iron oxides, every other natural formation destroyed. Craters, some from asteroid impacts and others being scars left from the invasion, littered the planet's southern hemisphere, the remains of the Martian civilization long buried.

Environment
Mars used to have a range of Earth-like environments, although the planet as a whole was quite cool compared to Earth. After the invasion, Mars' atmosphere became thinner, comprised of 95% carbon dioxide and less than 1% oxygen, with nitrogen and argon taking up the rest of its composition. Its temperatures varied to an even greater extent, averaging at inhospitably cold temperatures, with its pressure reduced to 1% that of Earth. Mars' weather was known to consist of dusty winds, often throwing rocks at high speeds. During the Trans-Galactic War, human terraforming returned Mars to an Earth-like atmosphere, but its environment remained desert-like.