Top 12 Moons of The Solar System (Part 2)

Part deuce of the top 12 moons. Part one here, in case you missed it. As you learned in the first post, there is a huge amount of diversity among the moons in our solar system. There are big ones, there are small ones, there are wet ones, there are dry ones, ones made out of rock, ones made out of ice.

They are pretty crazy, and for the most part, each moon has its own personality. Just like say, you were sitting in a lecture hall with 170 students. They would all be students, but different in their own ways. This list is just a fraction of all these moons, and volumes could be, and have been, written about each one of them. These are just some of my favorites, just like a professor might have his favorite student. Or a blogger might have his favorite followers.

So without further bantering, lets finish my list:

6) Ganymede:

Ganymede as seen from the Galileo Spacecraft.

Satellite of Jupiter. Radius: 2634.1 ±0.3 km (1636.75 mi). Discovered: January 7, 1610.

The largest of the Galilean moons and the largest in the Solar System. Ganymede is 8% larger then Mercury, but because Ganymede is mostly made up of silicate rock and water ice, it is 45% of Mercury's iron-rich mass. If it orbited the Sun, rather then Jupiter, it would be considered a planet. Ganymede is the third Galilean moon out from Jupiter, and is the only known moon to have it own magnetosphere, created by convection in a liquid iron core.

Ganymede also has a thin oxygen atmosphere, but nothing breathable by humans. Light regions crisscrossing the surface are probably the result of tidal heating causing tectonics. This heating is thought to also create a liquid water ocean about 200km under the crust, where there might be life. Ganymede is named for another lover of Zeus, except rather then a female, Ganymede is the only male figure. The handsome son of a king, that Zeus, in the form of an eagle, transported to heaven.

5) Charon:

Pluto and Charon from the Hubble Space Telescope.

Satellite of Pluto. Radius 603.5 ±1.5 km (375 mi). Discovered: June 22, 1978.

Little is known about Charon as of right now. Speculation can be determined from measuring surface brightness (a term known in astronomy as albedo) and its interactions with Pluto. It is thought to be composed of mostly water ice and rocks, but how its mixed together exactly is a matter of debate. But it is certain it has less rock then Pluto, and might have even been created by an impact into Pluto. The New Horizons probe is set to visit in 2015, and laying some of these questions to rest.

The other thing is, is it really even fair to call Charon a moon? For most moon's and their planet, the center of gravity between the two of them is somewhere inside the planet, not so for Pluto and Charon. Charon has 11.6% of the mass of Pluto, putting their center of gravity in space, between the two. So, some argue they are really a double dwarf planet.

Pluto also has two other moons, Nix and Hydra, discovered in 2005, which orbit the same point in space as Charon and Pluto, but not large enough to be spheroidal. In addition, many other dwarf planets in the Kuiper Belt are known to have moons: Eris has Dysnomia, Haumea has Namaka and Hi'iaka. These are some of the newest found moons and are helping to build an understanding to Kuiper Belt dynamics.

4) Io:

Io by NASA's Voyager 1 space probe.

Satellite of Jupiter. Radius: 1,821.3 km (1131.7 mi). Discovered: January 8, 1610.

This is the innermost Galilean moon, it also suffers the most tidal heating generated by friction between it, Jupiter, and the other large moons. This makes Io the most geologically active object in the Solar System, with over 400 active volcanoes! The surface is also dotted with over 100 mountains, some with peaks taller then Earth's Mount Everest. It's appearance has been likened to that of a pizza or a teenager's face.

The extreme volcanism also produces plumes of sulfur. Most of the surface is covered with a layer of sulfur an sulfur dioxide frost, while the rest of the planet is mostly made up of silicate rock around a sulfide iron core. The ejecta from Io's volcanism also provide material a thin atmosphere and Jupiter's magnetosphere, as well as a plasma torus around Jupiter. Io is named after another lover of Zeus, this one was a priestess of Hera.

3) Titan:

Light reflecting off of a northern lake (Jingpo Lacus) on Titan, seen by Cassini.

Satellite of Saturn. Radius: 2,576 ±2 km (1600.65 mi). Discovered: March 25, 1655.

The largest and first known moon of Saturn, and one of the most compelling objects of study right now in our Solar System. It is the only natural satellite known to have a dense atmosphere, mostly nitrogen with methane and ethane clouds. Titan is the only other object, besides the Earth, with clear evidence of stable bodies of surface liquid. It has seas of hydrocarbons. An entire hydrological cycle exists there, like there is on Earth: rain, lakes, rivers, ponds, seas, evaporation; but it is all comprised of liquid hydrocarbons like methane and ethane.

This has lead Titan to be an exciting subject, it may resemble an early, prebiotic Earth; or there maybe even be microbial life on Titan. So much more needs to be studied on this moon. There are indications of cryovolcanism and mountain forming and wind erosion, it can also be likened to a much colder Earth. In fact, the water that is there is in the form of solid ice, though there might be an subsurface liquid water ocean.

So much more can be said about Titan, it really is something to check out. Books have been written about this moon. Titan is unusual in its naming too, not named after an individual in mythology, it is named for the Titans, the brothers and sisters of the Greek god Cronos (Saturn in Roman).

2) Europa: 

Both Halves of Europe as seen by the Galileo Spacecraft.

Satellite of Jupiter. Radius: 1569 km (974.9 mi). Discovered: January 8, 1610.

The second Galilean moon out from Jupiter, Europa hides a stunning surprise. Slightly smaller then the Earth's Moon, Europa is mostly made up of silicate rocks with an iron core. There seems to be a tiny atmosphere of oxygen too. The surface is made of ice water, and one of the smoothest in the Solar System. What is just below this icy exterior is the great surprise. A liquid water ocean.

This ocean is generally accepted to exists by today's astronomers. Enough study of the dynamics of the planet just about proven it, aside from taking a dive in for ourselves. It would be created by a combination of thermal heating from radioactive elements in the core and tidal heating from friction with Jupiter. It is the most promising place for life in our Solar System outside of the Earth. Oh yeah, and it's single planetary subsurface ocean would be larger then all the water on Earth put together, not to shabby for a moon about a quarter our size.

The lines crisscrossing Europa's surface are cracks in the ice, from this tidal heat. In those cracks, it is thought, that occasionally the ocean might seep up. The red colors you see in images of Europa are organic compounds, not necessarily life, but carbon-based. It could either be life, or it could be emissions from the inner core. The biggest problem for life, is that the ocean might be to salty or chemically imbalanced for it. But we know of so many extremophiles now, life that thrives in extreme environments, that this place is promising.

Europa's namesake almost seems silly now, but it is another lover of Zeus, in the form of a white bull this time. She was the daughter of a king, but part god, and abducted, she became the mythical queen of Crete. Somehow this also becomes the namesake for Europe, and it I guess she is supposed to analogous to Athena, which isn't so bad.
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I bet you are wondering who is number one? Well, that depends on when you are reading this, you might already see who is number one. But that's OK, I hope you enjoyed this post and learned a couple things. Maybe even 5 things. But number one deserves it's own post... It's THE Moon by the way.

Posted in Charon,Europa,Ganymede,Io,Moon,Moons,Titan 15 comments