For ages, people have looked up at the stars and wondered what else is out there and while we may live in the age of rapid scientific advancement, we are still being baffled by the happenings of our own solar system. We have been to the moon, landed explorers on mars and have had satellites go even beyond and the information they have retrieved is truly astonishing. Pictures of planets that before where only accessible via telescopes during certain times of days during certain seasons during certain weather conditions have turned into twenty-four hour coverage allowing us to do live comparisons amongst which we have noticed certain planets have lunar systems that baffle us. The best example would be the Galilean Satellites of Jupiter. Back…show more content… These moons are both about the same size with Callisto being 4,820 kilometers in diameter and Ganymede being 5,260 kilometers in diameter so really only a difference of 440 kilometers which in objects this colossal is only a marginal difference. Both moons are also composed of rock and ice with craters populating their surfaces. The only difference when considering their surfaces is that while Callisto is heavily cratered with a surface dating back to when it was most likely formed, Ganymede is still geographically active with tectonic activity. There are regions that are lighter only possessing cuts, grooves, and ridges that conceal parts of older and much darker surfaces which in being older are also more cratered. As far as their interiors go, "it is speculated that Ganymede has a liquid, iron-rich core responsible for driving its magnetic field (Ganymede is the only moon in the Solar System to have its own magnetic field) with perhaps a saltwater ocean within 200 kilometers of its surface. Callisto may also harbor a thin ocean, but its interior is much less differentiated than Ganymede's – that is, it hasn't separated out into compositionally distinct layers"(Baldwin). Two moons that originated around the same time but due to the difference in location, their state of composition are really further apart than they seem and that is why it is important to…show more content… From what astronomers have been able to gather, it seems as though, "Callisto is the stereotypical outer solar system satellite... the surface is very icy and dates back four billion years. Beneath the icy crust is possibly a salty ocean supported by a deeper rocky interior"(Lasp.colorado.edu). As far as more quantitative theories are concerned, "Callisto has the lowest density (1.86 gm/cm3) of the Galilean satellites...Callisto appears to be composed of a crust about 200 kilometers thick. Beneath the crust is a possible salty ocean more than 10 kilometers thick. Beneath the ocean, is an unusual interior that is not entirely uniform nor does it vary dramatically" (Hamilton). This shows that from our distant observations accompanied by most data coming from our pictures and seeing how objects interact with the moons we have been able to discern this information about Callisto. All we know and can theorize about Ganymede is that the, "surface is rich in water ice and Voyager and Galileo images show features which are evidence of geological and tectonic disruption of the surface in the past...scientists expected Ganymede's interior to either consist of: a) an undifferentiated mixture of rock and ice or b) a differentiated structure with a large lunar sized 'core' of rock and possibly iron overlain by a deep layer of warm soft ice capped by a thin cold rigid ice