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Definition: Ganymede from Philip's Encyclopedia

Largest of Jupiter's Galilean satellites, with a diameter of 5,262km (3,270mi). Its cratered terrain is covered with grooves suggesting recent geological activity.


Summary Article: Ganymede
from Collins Dictionary of Astronomy

The brightest and largest of the four Galilean satellites of Jupiter. With a diameter of 5262 km it is the largest satellite in the Solar System. It is in fact larger in diameter than the planet Mercury but is only half as massive. It has an albedo of 0.42 and a density of 1.94 g cm–3. There are two main types of surface feature: ancient darkish heavily cratered terrain and the younger brighter regions, which have long parallel grooves or sulci. The two types intermingle, giving a complex surface. The largest single feature on Ganymede is the vast dark area Galileo Regio with a diameter of 4000 km. The most ancient craters – ghost craters or palimpsests – are barely visible in the dark areas such as Galileo Regio. Some of the younger craters are surrounded by bright rays of exposed ice. The grooved terrain consists of parallel mountain ridges up to 1 km high, 10 to 15 km apart, which wander for thousands of kilometers across the surface forming intricate patterns. From data collected by the Galileo spacecraft, scientists have surmised that Ganymede's internal structure consists of three layers: a compact core consisting of molten iron or iron and sulfur, a surrounding mantle made up of rocky silicates, and an outer shell of ice. As in the case of Europa and Callisto, evidence has been discovered of a tenuous oxygen atmosphere, resulting from charged solar particles breaking down water molecules in the icy crust. See also Jupiter's satellites; Table 2, backmatter.

© Market House Books Ltd, 2006

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