Tidal forces of orbiting body. Gases at different pressures reach different resting temperatures. It doesn't have to be water / water ice. Just look at the temp of Venus compared to that of Mercury. If Mars had more of an atmosphere (and magnetosphere) then it would also get warmer, without the need to move the position of the planet. Basically, the distance you are from the parent star doesn't have a direct co-relation with the surface temperature of the planet. Other things also have to be taken into account. Like the density of the planet, if it has a magnetic field, internal heat of the planet, composition of the atmosphere and density of that atmosphere. IIRC that is.
