We used the FLOWGO thermorheological model to examine the effects of Martian gravitational and environmental conditions on the cooling-limited behavior of lava flowing in a channel. The largest effect is due to the lower gravity on Mars as compared to Earth, which causes lava to flow more slowly. The lower velocity means that heat loss per distance down a Mars channel is greater even though the lower velocity also produces a higher percentage cover of insulating crust. Gravity alone causes the Mars flow to be >65 km shorter than an Earth flow with an equivalent volumetric flow rate. The cooler ambient Mars atmosphere causes a slight increase in heat loss by forced convection. This slows the flow a bit more, resulting in a very slight increase in heat loss per distance by all mechanisms, and decreases the modeled flow length by ~1 km, a difference well below our model uncertainty. Replacing terrestrial values of atmospheric density, viscosity, thermal conductivity, heat capacity, and cubic expansivity makes convection less efficient and increases flow length by ~15 km. Nevertheless, at the same volumetric flow rate, lava flows ~50 km less far under Martian conditions than under terrestrial conditions. Our specific model flow has a volumetric flow rate of ~5000 m3 s-1 and traveled ~190 km down a channel on a constant 7¿ slope. This volumetric flow rate is slightly less than the maximum rates during the 1783--1785 Laki eruption and is 5--10 times greater than those of typical Mauna Loa eruptions.