“No surprises in that. Anything alive couldn’t possibly breathe this air. There wouldn’t be enough oxygen in it.”
Ezhya confirmed. “No one comes near the Crystal Wastelands. Many have tried. Some of the desert kids go there. Apparently, they ride boards on the air in the crater. It is dense and grey and makes their voice go funny. If they fall off they die.”
I translated for Dr Scott, who nodded. “That sounds like sulphur hexafluoride all right. It’s the heaviest gas known. When you put it in a tank, it looks like water. You can float things on it. We only know it as an artificial product. Production requires free fluorine gas, which is one of the most reactive substances known.”
Asto, I knew, was extremely rich in fluorides.
Dr Scott stared at the screen again. “It’s also the stronges
