Methone, a moon of Saturn only about three kilometres across, has no observed craters larger than 130 metres: its porous icy surface may slowly shift and erase impact scars, while Saturn’s tides and the moon’s rotation mould it into a smooth, egg-like shape. - Space Daily

Saturn’s satellite system ranges from Titan, larger than Mercury, to bodies so small that a brisk cyclist could cross them in minutes. Methone belongs near the lower end. It measures only about three…