The sun is always just about to rise. Mercury rotates so slowly that you can walk fast enough over its rocky surface to stay ahead of the dawn; and so many people do. Many have made this a way of life. They walk roughly westward, staying always ahead of the stupendous day. Some of them hurry from location to location, pausing to look in cracks they earlier inoculated with bioleaching metallophytes, quickly scraping free any accumulated residues of gold or tungsten or uranium. But most of them are out there to catch glimpses of the sun.

Mercury’s ancient face is so battered and irregular that the planet’s terminator, the zone of the breaking dawn, is a broad chiaroscuro of black and white-charcoal hollows pricked here and there by brilliant white high points, which grow and grow until all the land is as bright as molten glass, and the long day begun. This mixed zone of sun and shadow is often as much as thirty kilometers wide, even though on a level plain the horizon is only a few kilometers off. But so little of Mercury is level. All the old bangs are still there, and some long cliffs from when the planet first cooled and shrank. In a landscape so rumpled the light can suddenly jump the eastern horizon and leap west to strike some distant prominence. Everyone walking the land has to attend to this possibility, know when and where the longest sunreaches occur-and where they can run for shade if they happen to be caught out.

Or if they stay on purpose. Because many of them pause in their walkabouts on certain cliffs and crater rims, at places marked by stupas, cairns, petroglyphs, inuksuit, mirrors, walls, goldsworthies. The sunwalkers stand by these, facing east, waiting.

The horizon they watch is black space over black rock. The superthin neon-argon atmosphere, created by sunlight smashing rock, holds only the faintest predawn glow. But the sunwalkers know the time, so they wait and watch-until- a flick of orange fire dolphins over the horizon and their blood leaps inside them. More brief banners follow, flicking up, arcing in loops, breaking off and floating free in the sky. Star oh star, about to break on them! Already their faceplates have darkened and polarized to protect their eyes.