In addition to what people have said about the temperature of surfaces in direct sunlight, you have to account for the power the electronics are using. The alum

In addition to what people have said about the temperature of surfaces in direct sunlight, you have to account for the power the electronics are using. The aluminum backplate is serving multiple purposes, but judging by the gap pad they are using and RF electronics in general, it's likely a non-trivial amount of power.