She couldn’t blame them. It was make-work. Something for the Martian soldiers on Ganymede to do to keep them busy. If Earth decided it needed Ganymede all to itself, four grunts walking around the greenhouse dome wouldn’t stop them. With dozens of Earth and Mars warships in a tense standoff in orbit, if hostilities broke out the ground pounders would probably find out only when the surface bombardment began.

To her left, the dome rose to almost half a kilometer: triangular glass panels separated by gleaming copper-colored struts that turned the entire structure into a massive Faraday cage. Bobbie had never been inside one of the greenhouse domes. She’d been sent out from Mars as part of a surge in troops to the outer planets and had been walking patrols on the surface almost since day one. Ganymede to her was a spaceport, a small Marine base, and the even smaller guard outpost she currently called home.

As they shuffled around the dome, Bobbie watched the unremarkable landscape. Ganymede didn’t change much without a catastrophic event. The surface was mostly silicate rock and water ice a few degrees warmer than space. The atmosphere was oxygen so thin it could pass as an industrial vacuum. Ganymede didn’t erode or weather. It changed when rocks fell on it from space, or when warm water from the liquid core forced itself onto the surface and created short-lived lakes. Neither thing happened all that often. At home on Mars, wind and dust changed the landscape hourly. Here, she was walking through the footsteps of the day before and the day before and the day before. And if she never came back, those footprints would outlive her. Privately, she thought it was sort of creepy.

A rhythmic squeaking started to cut through the normally smooth hiss and thump sounds her powered armor made.