Ganymede - largest moon in the solar system

Jupiter at 21.00 UTC on the 14th April 2015 - taken with my 127mm Meade Refractor and Canon 600D DSLR camera.

Jupiter's largest Galilean moon, Ganymede can be seen in the above image as a small black dot, transiting Jupiter's disc.  Io, the innermost and volcanically active Galilean moon,  can be seen just to Jupiter's lower left.  Europa can be seen further out.   I could see Callisto further out still but this moon was outside the field of view captured by my camera.

Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively. It has a diameter of 5,268 km (3,273 mi), 8% larger than that of the planet Mercury, but has only 45% of the latter's mass. Its diameter is 2% larger than that of Saturn's Titan, the second largest moon in the solar system. It also has the highest mass of all planetary satellites, with 2.02 times the mass of our Moon.

  

Ganymede has a magnetosphere, which implies the presence of a liquid iron core. The moon is comprised of silicate rocks and water ice and has a surface pocked with impact craters,. It is also considered likely that Ganymede hosts a subterranean salt water sea which along with Europa's subsurface ocean may harbour primitive extra terrestrial life.

Ganymede - Credit NASA Galileo Orbiter

Credits: Wikipedia and NASA