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Ice spires on Callisto. Artwork of ice spires (around 100 metres tall) on the surface of the Jovian moon Callisto. The moons parent planet, Jupiter, is in the sky, centre, with the other major moons either side of it. From the left, they are Ganymede, Io (casting a shadow on Jupiter) and Europa (covering Jupiter??s might side). It is thought that these spires formed from an ancient impact billions of years ago. They are very slowly eroding over time, the ice subliming and dust within the ice accumulating to absorb sunlight and continue the erosion. The Callisto-Jupiter distance is around 1.8 million kilometres, and Jupiter is around 140, 000 kilometres across.