... Tonight's Sky . ... Observing . ... Saturn's spongelike moon . ... Red denotes carbon dioxide ice (dry ice). ... We think that ordinary carbon dioxide will evaporate from Saturn's moons over long periods of time," said Cruikshank, "but it appears to be much more stable when it is attached to other molecules." ... Only registered members of Astronomy.com are allowed to comment on this article. ... Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter. ...