Weird Fantasy #10

A rocket ship crew arrive at Saturn's ring, made up of moonlets, and Stinton and Gentry's job was to study these up close by landing on one of them. However, when the ship returns to pick them up eight hours later, the two men are missing, so Commander Maxwell orders one of the moonlets brought aboard so that it could be taken back to Earth, where it is discovered the moonlet is actually a living spore.