Walking, in fact, took more of his attention than he expected, distracting him from the geology.

His suit would have been too heavy for him even to lift on Earth. And, being pressurized, it was about as stiff as a rubber tyre. But because of the low gravity, his mobility wasn’t much reduced from what he could manage on Earth.

He found that trying to walk heel-to-toe, as he did on Earth, was difficult and seemed to eat up energy. He kept tumbling away from the surface, as if he was walking across a trampoline; he didn’t feel as if he was stuck down properly to this light little world, and his overpowered Earth muscles kept throwing him off.

The best way to move was something like a lope. He would push off with one foot, shift his weight, and land on the other foot. It seemed to him he was covering ten feet or more with every step. But that couldn’t be right; the Moon must be fooling him again.

However far it was, however long he was up, every step kept him off the ground for several heartbeats, and he had to watch where he came down, on a rock or in an ankle-snapping crater. The trick was to anticipate each next step as he flew across the ground, shifting his weight and pushing off as soon as he landed, working rhythmically, like loping across a stream. It was demanding, and he couldn’t take his eyes off the ground for long. But he could relax in mid-step, unlike a runner on Earth, and it was amazing how that simple thing conserved his energy. It seemed to him he would take a long, long time to get tired.

He could sense his inertia, though.

It was hard to get moving; he had to thrust his body forward to get underway, as if he was walking into a wind. And to stop, he had to dig in his heels and lean back. He felt as if he was scuffing at this pulverized surface to which he was lightly bonded, trying to move his massive Earth bulk.

It was the separation of mass and inertia; the gravity here was so weak the effects of his mass were reduced, and inertia dominated. Sir Isaac Newton, you should have been up here. You understood all this, without having to fly to the Moon.

When he got tired, the stiffness of his suit actually helped. He could stop where he was and just slump inside his suit, and if he gave up the effort of trying to move the damn thing he could just rest against it.

When he looked across to Geena, she was loping along in much the same way. With her body dipping, stiff-legged, at every stride, she looked like a giraffe running across some Godforsaken piece of veldt, dipping into the swelling crater pits. He stifled a laugh.