Composition Near-IR spectra of dark cratered plains (red) and the Asgard impact structure (blue), showing the presence of more water ice ( absorption bands from 1 to 2 µm )  and less rocky material within Asgard. The average density of Callisto, 1.83 g/cm 3 ,  suggests a composition of approximately equal parts of rocky material and water ice , with some additional volatile ices such as ammonia .  The mass fraction of ices is between 49–55%.   The exact composition of Callisto's rock component is not known, but is probably close to the composition of L/LL type ordinary chondrites , which are characterized by less total iron , less metallic iron and more iron oxide than H chondrites . The weight ratio of iron to silicon is 0.9:1.3 in Callisto, whereas the solar ratio is around 1:8.  Callisto's surface has an albedo of about 20%.  Its surface composition is thought to be broadly similar to its composition as a whole. Near-infrared spectroscopy has revealed the presence of
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.