The Galilean Moons Of Jupiter

This is the first paper I had to write for Astronomy class, for those that have expressed interest in learning more! Enjoy!

Tonya Little
ASTR/PHYS 1504
M. Simmons
The Galilean Moons of Jupiter
The four largest moons of Jupiter are called Io, Europa, Ganymede and Callisto and they are all very different than each other. Collectively they are referred to as the Galilean satellites, after Galileo Galilei who was the first person to publish information about their discovery in 1610 (although there is a dispute between him and another scientist who claims to have discovered it around the same time). I will start by explaining a little bit about each of the larger moons.
Io is the most volcanically active body in the solar system known today, and is covered in sulfur. The gravity of Jupiter causes the volcanic activity on Io. Io is layered much like our earth. It has a core, a mantel of at least partially molten rock, with a solid rock crust that has a sulfur layer. Io is in a ‘tug of war ‘with Ganymede and Europa.
Europa’s surface is mostly made up of ice which appears to be covering an ocean of either water or slushy water. It has twice as much water on it than Earth does, and appears to have at least the potential of a habitable zone for life forms. Europa also has a layered structure with a possible metallic core, a rock layer around the core, a thick layer of ice, an ocean and a thin crust of water ice.
Ganymede is not only the largest moon in the solar system, but it is also the only known moon to have its own internally generated magnetic field. It has a layered structure just like Europa’s with the layers of ice and water, and a possible metallic core, but it doesn’t have the ocean underneath the crust.
Callisto is covered in craters, some of which appear to be very ancient along with newer ones that show current activity on the surface. There is a less defining layering effect within Callisto, it might have a very small core, and the rest of it is made up of rock and ice mixed together.
The moons all keep the same face pointing towards Jupiter which means that they each orbit once on their axis for every time they orbit Jupiter. However they all have a different rate at which they orbit Jupiter. Europa’s orbital period is twice that of Io’s, and Ganymede is twice that of Europa’s orbital period. This means that each time that Ganymede goes around Jupiter, Europa goes around twice and Io goes around four times.
Next I will discuss the Galileo probe. The Galileo probe was launched in 1989, but didn’t start its tour of the Jovian system until 1995. It made many trips around Jupiter and the moons to gather data. The probe was on its mission for 14 years, traveled more than 4.6 billion kilometers, and returned 33 gigabytes of data which included 14,000 pictures. This probe was the first to fly by an asteroid, to discover a moon of an asteroid and also provided the only direct observations of a comet colliding with a planet. It also was the first to measure Jupiter’s atmosphere with a descent probe as well as the first to conduct long-term observations of the Jovian system from orbit.
The Galileo probe discovered many new things about Jupiter and the larger moons. This new information included the fact that Jupiter has large thunderstorms many times larger than ours here on Earth, with lightening strikes up to 1000 as powerful as ours. It allowed us to observe the atmosphere and study the winds and clouds of Jupiter, giving us more information about how Jupiter evolved. The probe studied the global structure and the magnetic field, as well as discovered that the rings around Jupiter are made up of dust grains that have been blasted off of the surface by meteoroids. The Galileo probe also was able to tell us that the volcanoes on Io are much hotter than those on Earth, however this is probably much like Earth’s early days, which gives scientists an idea of what Earth was like billions of years ago. Images that the Galileo probe has taken of Europa show that there are broken pieces of ice which are larger than cities, that have drifted apart. There is also evidence that there is a salty ocean deep below the ice. Europa also appears to be fairly young since it doesn’t have many craters, and that it has an atmosphere of oxygen. Galileo also showed us evidence that Ganymede has its own magnetic field, a metallic core and possibly also a layer of liquid saltwater. The Galileo showed us that there might possibly be an ocean deep within Callisto also which gives it a magnetic field as well. The Galileo probe visited each moon several times and also went around Jupiter 34 times during its mission. It was crushed by Jupiter’s atmosphere in September 2003. It was deliberately destroyed to prevent the possibility that it would crash into Europa and contaminate any life that may be there.
The Galileo probe visited other places during its 14 year flight. It took pictures of Asteroid 243 Ida and its moon Dactyl and also did a flyby of the Asteroid Gaspra. The probe also did flybys of Venus, Earth, and the Comet Shoemaker.
During its mission, the Galileo probe was exposed to a much hotter environment than planned, so technicians created sun shades. The top of the probe also had to be pointed at the sun which was covered by an umbrella-like shade. The probe also had problems with its high-gain antenna, when some of them wouldn’t deploy. Despite having a special team working on it, they weren’t able to get them to let down and had to work with the low-gain antenna instead. This caused some communication problems, however the probe was still very successful using the tools it had available. The data just had to be sent at a much lower data rate. One of the items that was put in place to compensate for the loss of the higher speed data rate was a tape recorder which would hold large amounts of data until it could be compressed and sent back to earth. The probe also experienced problems with its tape recorder when it failed to rewind properly. However scientists were able to get it working properly but used it conservatively after that incident. It also had a portion of the tape that had been stuck in constant rewind, which caused stress on that part of the tape. That section of the tape was put “off limits” for recording any further data, or even getting the data that was on it. There were some images of the probe approaching Jupiter on it that were lost in the process.

There is a mission up for proposal to Jupiter called Prometheus One, which has a launch date of 2015 if approved.


Sources:
http://solarsystem.nasa.gov/planets/profile.cfm?Display=Moons&Object=Jupiter
http://astronomyonline.org/SolarSystem/GalileanMoons.asp
http://solarsystem.nasa.gov/galileo/?CFID=34138222&CFTOKEN=af9411b076752b08-37D41C68-0183-B17D-4AD785FE42083590
http://www.jpl.nasa.gov/webcast/galileo/
http://www2.jpl.nasa.gov/files/status/gl951101.txt