Slaves of Mercury

How long was it since they had started out on the first flight that man had taken into outer space-he and those stanch comrades? Five years? God! Had it been so long? Yet here he was, back on Earth again, the kindly, blessed Earth their eyes had clung to when they were fighting desperately for their lives against the protoplasmic things that inhabited Ganymede.
There was a tap on Hilary's shoulder, light, electric, yet strangely heavy in its implications. Hilary turned his head sharply, saw the landscape blotted out by a huge overshadowing bulk. Five years in a hostile universe had made him cautious. He pivoted on his heels and rose in a single flowing motion, stellite blade ready for instant action.