The eclipses were often spectacular. Just before it slid between Ganymede and Lucifer, Europa would become an ominous black disc, outlined with a ring of crimson fire, as the light of the new sun was refracted through the atmosphere it had helped to create.

In less than half a human lifetime, Europa had been transformed. The crust of ice on the hemisphere always facing Lucifer had melted, to form the Solar System's second ocean. For a decade it had foamed and bubbled into the vacuum above it, until equilibrium had been reached. Now Europa possessed a thin but serviceable – though not to human beings – atmosphere of water vapour, hydrogen sulphide, carbon and sulphur dioxides, nitrogen, and miscellaneous rare gases. Though the somewhat misnamed 'nightside' of the satellite was still permanently frozen, an area as large as Africa now had a temperate climate, liquid water, and a few scattered islands.

All this, and not much more, had been observed through telescopes in Earth orbit. By the time that the first full-scale expedition had been launched to the Galilean moons, in 2028, Europa had already become veiled by a permanent mantle of clouds. Cautious radar probing revealed little but smooth ocean on one face, and almost equally smooth ice on the other; Europa still maintained its reputation as the flattest piece of real estate in the Solar System. Ten years later, that was no longer true: something drastic had happened to Europa. It now possessed a solitary mountain, almost as high as Everest, jutting up through the ice of the twilight zone. Presumably some volcanic activity – like that occurring ceaselessly on neighbouring Io – had thrust this mass of material skywards. The vastly increased heat-flow from Lucifer could have triggered such an event.

But there were problems with this obvious explanation. Mount Zeus was an irregular pyramid, not the usual volcanic cone, and radar scans showed none of the characteristic lava flows. Some poor-quality photographs obtained through telescopes on Ganymede, during a momentary break in the clouds, suggested that it was made of ice, like the frozen landscape around it. Whatever the answer, the creation of Mount Zeus had been a traumatic experience for the world it dominated, for the entire crazy-paving pattern of fractured ice floes over the nightside had changed completely.