... An artificial comet holds secrets to Earths life . ... Frozen comet had a watery past, University of Arizona scientists find . ... Current thinking suggests that it is impossible to form liquid water inside of a comet," said Dante Lauretta from the University of Arizonaт??s (UA) Lunar and Planetary Laboratory in Tucson, Arizona. ... Astronomers frequently refer to comets as dirty snowballs because they consist of mostly water ice, peppered with rocky debris and frozen gases. ... Find us on Facebook ...