“This is a gravity map,” Martin said, triumphant. “No, I don’t know why we can’t see anything inside that shell.” His voice practically boiled over with excitement. “But it’s man-made, there’s no alternative. I also have no idea what it’s made of. Harmony has some speculation, but it says I’m not complex enough to understand. Except if I was I couldn’t come downstream and explain all this, so…”