A newly released image of Pluto reveals what appear to be massive hills of water ice embedded in frozen flows of nitrogen—icebergs, if you will, that apparently broke away from larger masses of ice in the rugged highlands nearby. The photo, released yesterday and seen at right above, is a 340-km-by-500-km close-up of Sputnik Planum, the western lobe of a bright heart-shaped feature straddling Pluto’s equator. (Because water ice is less dense than nitrogen ice, bergs of such material would waft along just as they would in Earth’s seawater, the researchers explain.) Individual chunks seen in the image range from 1 to several kilometers long, and chains of the bergs seem to mark the edges of nitrogen glaciers flowing from the icy highlands onto a broad plain. Once on that lowland, the bergs are carried along by the slow-flowing nitrogen ice, often ending up clumped together in large groups (such as the 60-km-long Challenger Colles, upper right, a feature whose name honors the seven astronauts who died onboard space shuttle Challenger in 1986). The image, obtained just 12 minutes before the New Horizons craft swooped past Pluto last 14 July, was taken from a range of about 16,000 kilometers.