This Mars had a thicker atmosphere than most others (which is why it was able to support life), probably because of a recent volcanic eruption. It was warmer than most other Marses, and it's air was oxygenated and contained water vapour.
It had a bruised-purple sky, rather than the usual brown one.
Willis wanted to confirm his theory that life was present on this world because of a recent volcanic eruption. He proposed that they deploy a probe that would travel to Arabia - a region on the opposite side of the planet - as he believed that this is where the erupted volcano would be located.