Strange Moons Of The Solar System

A moon is a natural satellite that orbits a larger space object such as a planet or an asteroid. According to NASA, our solar system is home to over 200 moons, also referred to as satellites. This list seems to grow every year as missions into space reveal new and exotic moons. Most moons in our solar system swarm around the gas giants. Jupiter has 79 satellites just by itself, and Saturn is the current champ holding 82 satellites in its orbit.

Moons are also incredibly diverse. Some satellites, such as Earth's Moon, are large and act as a stabilizing force. Others are quite small, being only dozens of miles in diameter. Some have atmospheres while others feature icy oceans, and a few even broil in hellish volcanic activity. Some of these are so interesting that a future space traveler might forgo visiting the planet itself just to check out the far more interesting moons. Here are just a handful of the strangest moons in the solar system known to science.

Dactyl has the distinction of being the only moon known to orbit an asteroid. NASA reports that Dactyl's potato-shaped asteroid is named Ida (pun was not intended by the discovers) and is part of the objects in the asteroid belt between Mars and Jupiter. When the Galileo spacecraft flew by on its mission to Jupiter in 1993, it did a close flyby and noticed Dactyl. The moon itself is tiny, 0.99 miles at its longest, but it is spherical, according to space.com. This round shape itself is puzzling since anything that small would not have enough gravity to pull itself into a spheroid. In addition, the age of Ida and Dactyl are a bit of a mystery. Craters on Ida suggest that it is ancient, but it is also part of the younger Koronis family of asteroids dated to only one or two billion years ago. It is clear, however, that although right now Dactyl is the only moon to orbit an asteroid, we will undoubtedly find others.

Any place in space is dangerous for future space travelers, but Jupiter's moon of Io should have flashing lights surrounding it shouting, "Do not under any circumstances land here." Io is Jupiter's fifth moon, according to space.com, and with a mean radius of 1,131.7 miles, it is a touch bigger than our Moon. It is also cold, with temperatures averaging about 202 degrees below zero. This is cold enough that sulfur dioxide freezes to form snowfields. But temperatures this low are not unusual for a moon this far from the Sun. The danger comes from Io being the most hellish place in the solar system. This moon features hundreds of volcanoes that launch lava miles up and plumes of sulfur hundreds of miles higher. Lava bubbles up, filling impact craters and covering the landscape so thoroughly that Io is constantly being resurfaced.

Io became the solar system's hell through gravity. NASA explains that it is tugged by Jupiter's gravity but also counter yanked by the large moons of Europa and Ganymede. These tidal forces cause the surface of Io to bulge up and down by 330 feet -– and this is a tide of rock, not like the watery tides on Earth that differ by only 60 feet.

Callisto, Jupiter's fourth moon, may well be the most banged-up looking moon in the solar system. As analyzed by Britannica, this 3,000-mile diameter satellite is about half as dense as our Moon, which indicates that it is half rock, half ice. Callisto shows an inordinate amount of pockmarks left from impact craters over the eons. What this usually indicates is that there is little geologic activity within the moon since if there were, such as active volcanoes and the like, the landscape would get remade. In essence, Callisto has long been discounted as dead a moon as can be in the solar system.

Or is it?

Recent evidence gathered by modern space exploration shows that there may be more to Callisto than meets the eye. Space.com reports that Callisto seems to have a fluctuating magnetic field that is caused by Jupiter's powerful magnetic field, creating an electrical current within the planet. This was supported by observations by NASA and the Hubble Space Telescope. It is suspected that this may be due to a salty ocean under the moon's crust which can conduct electricity.

Hyperion's claim to fame is that it looks like a spongy potato. This Saturnian moon is reported by space.com to be rather small. At its longest point, it is only 255 miles in diameter. What makes Hyperion unique is that it is the largest nonspherical moon in the solar system. Aside from not being round, it also appears to contain many porous structures, thus giving it the appearance of a sponge or a tufa rock. In addition, this moon does not rotate in a predictable way, and it speeds up or slows down in its elliptical orbit due to its relative position to the large moon Titan.

NASA argues that potatoes in space aren't born that way. Hyperion was likely a part of a larger moon that had been destroyed in a prior collision. The moon itself seems to also have a large amount of ice within its crater pores. The Cassini spacecraft discovered one other phenomenon associated with Hyperion. When it performed a close flyby in 2005, Hyperion sent a charge of static electricity at the probe. While Cassini was unharmed, scientists continue to study the data to understand future space hazards.

Several of Saturn's moons, including Pan, Daphnis, and Atlas, are classified together as shepherd moons. However, instead of herding sheep, these satellites herd rings with a gravity crook. These moons are tiny. According to NASA, the potato-shaped Epimetheus has an average 36-mile radius and is the largest shepherd moon. The others are much tinier. Atlas has an average radius of just 9.4 miles, while Daphnis is only 2.4 miles. The function of these shepherds is to clear spaces between Saturn's famous rings or, in the case of Atlas, trim the edge of one. They do this at a fast pace. Pan, for example, orbits Saturn in 13.8 hours while Atlas does it in 14.4. Consider that our Moon orbits Earth in a little under a month. What makes them even stranger is their irregular appearance: Atlas is pointy while Pan looks like a 1950's conception of a UFO. According to the New York Times, the shepherd moons are made mostly of ice and accrete even more ice as they make their endless revolutions around the planet. Other planets in the solar system have such shepherds for their less spectacular ring systems, including Jupiter and Neptune.

Obi-Wan Kenobi may have said, "That's no moon, it's a space station," in reference to the Death Star in "Star Wars: Episode IV – A New Hope," but had he seen Saturn's moon Mimas afterward, he may have uttered, "That's no space station, it's a moon."

Mimas is small, with an average 123-mile radius according to NASA and at only 115,000 miles out from Saturn has been subject to intense bombardment from asteroids. Most of these asteroid craters are large, with many over 25 miles wide. Yet these are small compared to a huge impact crater, called the Herschel Crater, which is 80 miles wide. This crater is located in such a way that it makes the moon look at first blush like Emperor Palpatine built it.

There is also another puzzle about Mimas that perplexes scientists. Because of its close elliptical orbit and because it is mainly made of ice, there should theoretically be ice volcanic activity such as on Enceladus. In fact, it has a more elliptical orbit which means there should be more tidal action to cause massive water geysers. Strangely, however, this moon does not have it. It seems to be completely frozen solid –- and there is no solid explanation of why. Space.com reports that this has led to a so-called "Mimas Test," in which any explanation of Enceladus's icy geyser action has to also explain why Mimas does not have any.

Our tour of the moons of the solar system ends with Triton, the largest of Neptune's moons, but its distinction is based not on size but on weird habits. According to NASA, this 1,680-mile diameter moon is unusual because it orbits in the opposite direction of Neptune's rotation, something called retrograde. Additionally, NOAA explains that Triton rotates at 157 degrees to the axis of Neptune's rotation. Practically speaking, what this means is that Triton's north and south poles alternately face the Sun. It is assumed that this causes wide disparities in any seasons on Triton. These strange characteristics are likely because Triton was originally a Kuiper belt object on the edge of the solar system that had been captured by Neptune's gravity. Scientists often compare Triton to Pluto, which is the large Kuiper belt object that had once been considered a planet.

Since Triton is so distant from the Sun, it is cold with an average of 391degrees below zero. Like other planets at such a distance, gasses freeze (particularly nitrogen on Triton), and volcanism, when it occurs, involves melted ice rather than melted rock. For example, one 5-mile high plume of water vapor was observed to have erupted from an ice volcano. Its icy covering reflects almost all light which contributes to its coldness.