Cassini's fly-by image of Ganymede and Jupiter from 2000 on its way to Saturn. Image credit: NASA/JPL/University of Arizona.

Cassini's fly-by image of Ganymede and Jupiter from 2000 on its way to Saturn. Image credit: NASA/JPL/University of Arizona.

Good morning and welcome back!

This week's topic is looking at the Solar System's largest moon- Ganymede! It is surprising that this moon does not get a lot of press compared to other lunar bodies. But we are going to look at some of the really cool information we've learned from Jupiter's moon!

1- It is very large! It is larger than Mercury and dwarf-planet Pluto at 5,262 km diameter! In comparison, Earth is 12,742 km! 

2- Ganymede is the furthest Galilean moon from Jupiter and takes about 7 Earth days to orbit Jupiter. How fast is that? About 39,165 km per hour! In comparison, Earth travels around the Sun at 110,000 km per hour. Weeeeeeee!

3- There might be life? We have information about this moon to have salty oceans that are being churned and warmed by the inner iron core and sealed from radiation by the frozen silicate crust. 

4- It is the ONLY moon to have a magnetic field! Although small and often masked by Jupiter's much larger magnetic field that tends to overlap its nearby moons, Ganymede's magnetic field is sustained by the possible convection of its inner core layers. Just like Earth's!

5- Seven spacecraft have been close by to take pictures! Pioneer 10 and 11 in 1973, Voyager 1 and 2 in 1979, Galileo in 1995, Cassini fly-by in 2000, and recently New Horizons in 2007! 

Surface of Ganymede as seen from Galileo in 2000. Dark and light terrains with heavily cratered areas make up the surface. So much ice! Image credit: NASA/JPL/Brown University

Surface of Ganymede as seen from Galileo in 2000. Dark and light terrains with heavily cratered areas make up the surface. So much ice! Image credit: NASA/JPL/Brown University

Thank you for reading and next week we'll have an update about our Moon to get you ready for International Observe the Moon Night (October 8th)!