 How did the Mercurians adjust to the heat?
Only the native waiters, the enigmatic, yellow-eyed Mercurians, seemed unaffected by the heat. One moment the garden was glowing in light, the next the hot black night swooped down on the revelers, pressing against their eyes like dark wool. For centuries they had lived most their lives beneath ground to escape the terrible rays of the sun. If the girl had been abducted, only Mercurians could have engineered it in the dark; and the Mercurians were a clannish lot. Jaro Moynahan In the East a sullen red glow stained the heavens like the reflection of a fire. "There are many of us here, Mercurians as well as Earthmen, who recognize the danger. Other Earthmen are in control of the mines and the northern plantations.
 They mostly lived under the ground.
 Their yellow eyes filtered the sun’s rays.  They mostly lived under the ground.  Their skin kept them cool.  They would sweat to cool off.