Mars is the fourth planet of the Sol system, adjacent to Earth, and bears a distinct reddish tinge due to the widespread presence of iron oxide on its surface. Few are aware that in the events following The First to Fall, Mars was rendered habitable by human life. Despite that alteration, however, Mars currently remains largely uninhabited by sentient life. The only permanent establishment is a mining operation conducted jointly by Empirical Industries and ARCHIE III.
The fiery appearance of Mars is caused by iron(III) oxide (rust) on its surface. Mars has half the radius of the Earth and only one-tenth the mass, being less dense. With the restoration of surface water to it, after the events of The First to Fall, its landmass is significantly less than Earth's, as well. Prior, it had been almost equal due to the scarcity of water.
The atmosphere of Mars, after its transformation, has been rendered suitable for human life. As such, it closely approximates Earth's atmosphere, becoming composed of approximately 21% oxygen, with the remainder being a mixture of inert gases such as nitrogen and carbon dioxide. Trace gases are also present to fill out the mixture properly.
With its restoration of a proper magnetic field and establishment of an atmosphere capable of shielding the surface from ionizing radiation, Mars' climate has been altered to one suitable for human habitation. Overall, it tends to a more tropical state that Earth's, generally, with larger temperate and tropical regions, and smaller arctic regions. Due to the similarity in axial tilt, the division of seasons is similar to Earth's, however, given the longer Martian year, seasons are significantly expanded all around.
The surface of Mars is primarily composed of basalt. The basalt tends to be more silica-rich than typical Earth basalt, perhaps more similar to andesitic rocks on Earth. Mars has several deserts, composed of a deep covering of dust as fine as talcum powder, resulting in the distinct possiblility of desert wayfarers finding themselves drowning in dryness.
Due to Mars' smaller size, the surface gravity of the planet is smaller than Earth's. Gravity at the equator is approximately half that of Earth's gravity -- a larger value than prior to its reformation, due to the improved amounts of heavy metals in its molten core.
Mars makes a complete orbit of the sun in 687 Earth days -- significantly longer than an Earth year. Despite this, the rotation speed of Mars is similar to that of Earth, for its day is 24 hours, 39 minutes, and 35.244 seconds long -- only slightly extended over an Earth day.
Mars is easily observed to have two moons: Phobos and Deimos. Observed from the surface of the planet, Phobos rises in the west, sets in the east, and rises again in just 11 hours, while Deimos, being only just outside synchronous orbit, rises as expected in the east but very slowly. Despite its 30 hour orbit, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars, and takes as long again to rise in the east.