There are at least 170 known natural satellites, or moons, in our Solar System. A number growing as discoveries are made. This excludes those orbiting small Solar System bodies, such as comets and asteroids. These moons vary across a wide range of size and features, making a number of them extremely unique places. 19 of them are large enough to be considered planets or dwarf planets if they directly orbited the Sun.
The large variety of moons make them one of the more interesting subjects in astronomy. Some of these moons may even have life or conditions similar to an early Earth. So, I figured I'd give you all a two-parter post of my "Top 12 Moons of The Solar System." Here is the first half, with plenty of pictures:
11 & 12) Phobos and Deimos:
|NASA images from the Mars Reconnaissance Orbiter.|
Named after Ares' twin sons, who attended him in battle, their names mean "fear" and "dread." The moons of Mars are a bit different, in fact are some of the tiniest moons in the solar system. And rather then sons, these moons are hypothesized to have been captured from the asteroid belt. Their characteristics are very similar to that of several asteroids, supporting this idea. This was a bit of a cheat on my part to include both as one, but they are pretty similar moons.
|Hyperion as seen from the Cassini Spacecraft.|
Hyperion is probably one of the weirdest moons of the solar system. It looks spongy in appearance and texture, it's density also suggests it may be full of vast cave systems. Hyperion is also oblong shaped, almost like a potato, and was the first non-round moon discovered and one of the largest. It also has a chaotic rotation, meaning is spins every which way. The heavy cratering is indication of a violent past, which may contribute to is chaotic nature. Hyperion is named after the Titan god of watchfulness and observation.
|Callisto as seen from NASA's Galileo spacecraft.|
As far as the four Galilean moons go (all of which will be on this list), Callisto is probably considered the most forgettable. It isn't the largest, the craziest, or the most likely to have life. It is just a little ball, 99% the diameter of Mercury (just a smudge smaller), and the furthest of the Galilean moons from Jupiter. Galilean begin the term for the moons of Jupiter discovered by Galileo Galilei.
There is a small chance of a subsurface ocean, but tidal heating from Jupiter isn't as strong on Callisto as it is on closer moons. But it also has low radiation levels, making it a good base of operations for future human exploration of the Jovian system. Callisto, like the other Galilean moons, is named after on of the many lover's of Zeus in Greek mythology.
|A Mosaic of Triton's Surface by Voyager 2.|
Satellite of Neptune. Radius: 1353.4 ±0.9 km (840.1 mi). Discovered: October 10, 1846.
There is something different about the largest moon of Neptune. The seventh largest moon in the Solar System is the only large moon with a retrograde orbit, meaning it orbits in a direction opposite of the planet's rotation. Triton is slightly larger and has a composition similar to that of Pluto's. Because of this, Triton is thought to have been captured from the Kuiper Belt. Triton is also one of the few moons known to be geologically active, with cryovolcanic and tectonic indicators, and a very thin nitrogen atmosphere. Triton is named after Poseidon's son, and was discovered only 17 days after Neptune's discovery!
|Mimas as seen from Cassini.|
Satellite of Saturn. Radius: 198.3 ±0.3 km (123.2 mi). Discovered: September 17, 1789.
Commonly known as the "Death Star" moon because of the humungous impact crater that nearly destroyed the moon. The crater is named Herschel, after the moon's discoverer, and is one of the largest in the solar system at about a third of the moon's diameter and wider then Canada. Fractures can be seen on the opposite side of the moon, created by shockwaves from the impact.
The moon itself is also unique. It is the smallest known astronomical body that is thought have enough self gravitation to create a spheroidal body. It isn't perfect though, it has a slight egg shape, more pronounce in some other Cassini photos. But it gives astronomers a working limit for hydrostatic equilibrium, which is used to determine dwarf planets from other small Solar System bodies, like asteroids and comets. Mimas is named after a Titan in Greek mythology, the son of Gaia.
That's all for today. Tune in for the rest tomorrow! Also, some facts for those wondering:
-We have not observed moons outside of our Solar System, but there are projects trying to determine if there are any! Mostly this is to see if there might be a habitable moon around a 'hot-Jupiter.'
- There are many small object moons in our Solar System, these orbit mostly asteroids, or other moons.
- Mercury and Venus have no known moons, certainly nothing larger then in a kilometer in length that is detectable. But there is evidence for lunar existence in the past. (Venus's retrograde rotation and Mercury's beat up surface)