Jupiter and its Great Red Spot have many moons spinning around it, about 61 in fact.  The four largest are called the Galilean Satellites, named after their discoverer Galileo Galilei in 1610.  Galileo had named them Cosmica Sidera “Cosimo’s Stars” but that changed after Simon Marvis claimed that he had discovered them at the same time as Galileo.  Marvis had named them in his book, names that were four of Zeus’ loves.  Scientists chose the individual names, no doubt for better cataloging.

The ladies are (closest to farthest order) Lo. Europa, Ganymede, and Callisto.

Lo is a volcanic moon full of eruptions, lava and gases.  Being the closest to the planets has some adverse affects.  The tidal forces of Jupiter cause it to flex and heat up inside.  Its surface has over 100 mountains, some taller than Mount Everest.  The surface is mostly silicate rock, covered by sulfur dioxide frost.  The volcanic plumes and lava flow create a variety of color.  Red, yellow, brown, black, green and orange make for an interesting looking moon.  What does it look like to you?

NASA’s Galileo space craft acquired its highest resolution images of  this moon on July 3rd, 1999

Europa is next, a smooth moon with cracks along the surface, almost like a red sphere of marble.  It is know as the smoothest natural body in the solar system  Geologists think that Europa may have liquid water under its icy surface, and possibly life.

Third in line from the great master is Ganymede, the Largest moon in our solar system.  If it wasn’t harnessed to Jupiter orbital strength it would be considered a planet of its own.  It is larger than Mercury but not so hot, actually it’s cold.  Geologists think that Ganymede once had plates like the Earth, but they froze together shortly after its birth.  Do you think that if it was in orbit around the sun, that it might have been a planet that could sustain life?

Last but not least of the four satellites is Callisto.  It is almost the same size as Mercury, they are sometimes called twins, but that is the only similarity between them.  Every square mile of Callisto is covered with craters, that’s a lot of holes.

The Galilean Satellites are unique for their size and vast differences, but there are many moons around Jupiter and many more in our solar system.  Go ahead look up Saturn’s great moon Titan or Pluto’s Charon, Nix and Hydra.  How many known moons are there around Neptune?  Explore the solar system and seek the answers.