... Comet Churyumov Gerasimenko in Crescent . ... Credit Copyright: ESA , Rosetta , NAVCAM; processing by Giuseppe Conzo Explanation: What's happening to Comet 67P/ChuryumovGerasimenko? As the 3-km wide comet moves closer to the Sun, heat causes the nucleus to expel gas and dust . ... Comet 67P , shown in a crescent phase in false color, should increase its evaporation rate as it nears its closest approach to the Sun in 2015 August, when it reaches a Sun distance just a bit further out than the Earth. ...