Mars is the fourth planet in the Solar System and is known as the Red Planet.
In late 2009, the planets in the Solar System began to align themselves, with Mars aligning itself, and a massive solar flare erupted from the Sun. The solar flare hit the Earth, but the planet's magnetic field protected it from the Sun's UV Rays. However, the combination of the alignment of the planets and the unprecendented amount of neutrinos the solar flare, caused the Earth's core to heat up its temperature so high, the Earth's crust became unstable and it caused the planet to come to an end in 2012.
When the apocalypse ended, the Earth is rendered uninhabitable and when time was reset to year one, Mars continued to remain in its orbit as the Earth now had a new landscape.