Mars (also known as the Red Planet, Sol IV or Sol Secundus) was once a cool Ae-Class world but was terraformed into a temperate Me-Class world. It is the most Earthlike world in the Sol System aside from Earth.
The first humans to step foot on Mars did so on March 23, 2029 near Valles Marineris. After four missions, the last one leaving Mars on July 4, 2039, Earth sent out reusable rockets full of compressed chlorofluorocarbons to Mars. Their payload was launched into the Martian atmosphere and crashed landed on the surface. This caused the compressed gasses to be ejected into the atmosphere. For a decade, the rockets kept bombarding the surface with massive containers of CFCs. This caused a global change in the temperature.
As technology improved, driver probes were sent to the asteroid belt and diverted many ice asteroids into the Martian orbit and skimming them across the Martian atmosphere.
While diverting asteroids, one probe accidentally discovered an iron rich dwarf planet. Scientists on Earth debated moving this world into Martian orbit to keep future inhabitants of the terraformed world safe from solar radiation. After years of debate and inventions, this was accomplished. The new moon was given the name Simud. Mars was completely terraformed by 2475.
Mars has a population of just over 7 billion spread across the cool tundras, forests, deserts, and cities of Mars. Thanks to the low gravity, Martians are taller and weaker than terrestrial humans.
Mars is the second oldest human colonized world and second most diverse culturally as nearly every country sent colonists to Mars, even religious groups that lived in the higher elevations moved and built monasteries and temples in the now snow covered higher elevations.
Many groups who’d grown up near the Mediterranean moved to the new Hellas Sea where they set up many small fishing cities.
Due to its distance from Sol, most of the climates are cooler than their Earth counterparts. The four major volcanoes on the planet jut out of the atmosphere entirely. Many of the major cities on Mars exist in some of the larger craters near the local atmospheric datum. Each city has its own local weather. Note that before terraforming, Mars had much lower pressure and average temperature.
At higher elevations, the terrain resembles terrestrial alpine biomes and the Hellas Sea resembled the Mediterranean Sea. The poles are larger than their earth counterparts and the winds on the planet are much more predictable than their Earth counterparts.
The native human Martian population is split into two groups. Since the gravitational pull of Mars is similar to that of Mercury, half of the population have since genetically engineered themselves to be able to fly using wings. They refer to themselves as Aerians. The non-winged inhabitants of the planet simply refer to themselves as Martians. This has caused a genetic shift over the millennia since the colonization of the planet, so much so that interbreeding is not naturally possible with Aerians and Martians.