The weather conditions on Mars are chaotic and unpredictable. The sky can be pink and cloudless, filled with dust blown from the Martian surface or filled with ice clouds which form as the temperature drops. The shift in weather is due to three important factors: the thin atmosphere, the elliptical orbit around the sun, and the strong interactions between dust and ice clouds in the atmosphere. Mars has permanent ice caps at both poles composed mainly of solid carbon dioxide (dry ice). They exhibit a layered structure with alternating layers of ice and dust. In the north, during summer, the carbon dioxide completely sublimes (converts from solid to gas), leaving a residual layer of water ice. It is unknown if a similar layer of water ice exists below the southern caps since its carbon dioxide layer never completely disappears. The mechanism responsible for the layering may be the climate changes in the inclination of Mars' equator to the plane of it's orbit. There may also be water ice hidden below the surface at lower latitudes. In addition, seasonal changes cause changes in the global atmospheric pressure by about 25% (as measured at the Viking lander sites).

Mr Slingsby has guests

Mr Slingsby was happy with his brand new home way out in the middle of the Hellas basin, but he was more than a little concerned when representatives of the area's original inhabitants paid him a visit. He strongly suspected they were not about to engage him in small talk and ask after his health. On reflection he thought the use of nuclear weapons to terraform the region was just a little insensitive to the native species rights and requirements. Dogs make very good pets, but very poor neigbours.