Stories from Callisto

Callisto is Jupiter’s second largest and outermost moon, and numbers among the most heavily cratered worlds in our solar system. This cold moon formed slowly from the gradual coming together of lumps of rock and ice. It was never molten, and its landscape, unlike that of its neighbour Io, has never had its surface cleared of old scars by volcanic processes. In the billions of years since its slow creation, Callisto has become totally covered in impact craters, new on top of old. Its landscape, perhaps the oldest in the solar system, bears the scars of countless impacts.

Callisto mosaic

Jupiter's moon Callisto, this hemisphere dominated by the Valhalla multi-ring basin. NASA-JPL/Caltech: PIA00080.

There is a whole world in our solar system where places take their names from Norse myth.

Among Callisto's ancient scars are distinctive multi-ring basins, the leavings of enormous impacts many millions of years ago. The largest of these basins, Valhalla, covers a considerable portion of the planetary surface, with concentric rings of upturned mountains and shattered rock extending up to about 1,900 km from its centre. The International Astronomical Union has assigned Callisto a theme, taking its names from the myths and folktales of the far north, including Norse, Chukchi, Inuit and Sami. Of its 154 names, 92 are of Norse origin.

Viking ships at sea by Lorenz Frølich

In the early decades of space exploration, lunar missions tended to have names associated with travel by land (Pioneer, Ranger) while those to more distant worlds, like Mars, had names associated with oceanic travel and exploration (Viking). The solar system is a vast cosmic ocean, its waves lapping on a lunar shore. Frieze by Lorenz Frølich (1820-1908), The Museum of National History, Frederiksborg Castle.