Mysterious moons of our solar system

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Charon​

Charon is the largest moon of the dwarf planet Pluto. It is technically the largest known moon relative to its parent planet in our solar system. But because Pluto is a dwarf planet, our own moon is still cited as the largest natural satellite. This mysterious and distant world was discovered in 1978. One of its defining geological features is Mordor Macula, a large reddish area near the moon's north pole named after the black land called Mordor in J.R.R. Tolkien's 'The Lord of the Rings.' Image: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker.

 

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Nereid​

Nereid, imaged here by Voyager 2 in 1989, is one of the outermost of Neptune's known moons. It is the third largest of the planet's satellites and is unique because it has one of the most eccentric orbits of any moon in our solar system: it is so far from Neptune that it requires 360 Earth days to make one orbit. Image: NASA.

 

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Epimetheus​

Epimetheus, a moon of Saturn, fascinates scientists because it shares an orbit with another moon of the planet, called Janus. Image: NASA/JPL-Caltech/Space Science Institute.

 

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Janus​

Janus and Epimetheus are both irregularly-shaped moons that orbit Saturn so close together that every four years the two satellites exchange orbital positions. Image: NASA/Jet Propulsion Laboratory/Space Science Institute.

 

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Epimetheus and Janus​

This complex interplay between Epimetheus and Janus takes around 100 days to complete and is akin to an orbital dance. Epimetheus (lower left) and Janus (right) are pictured about 40,000 km (24,854 mi) apart while circling Saturn. Image: NASA/JPL/Space Science Institute.

 

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Methone​

A small egg-shaped moon of Saturn, Methone is remarkably smooth and completely devoid of craters. The tiny moonlet orbits between the much larger moons of Mimas and Enceladus. Image: NASA/JPL-Caltech/Space Science Institute.

 

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Rhea​

Rhea is the second-largest moon of Saturn after Titan. A huge icy body with a rocky core, Rhea is heavily cratered with bright wispy markings. Research suggests that it could be capable of sustaining an internal liquid-water ocean through heating by radioactive decay. Image: NASA/JPL/Space Science Institute.

 

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Dione​

Dione is the densest of Saturn's moons with the exception of Titan. Its icy surface includes heavily cratered terrain, with many craters larger than 35 km (21 mi) in diameter. Image: NASA.

 

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Umbriel​

Umbriel is the darkest of Uranus' moons, a twilight world that reflects only 16% of the light that strikes its surface. Its one luminous spot is the Wunda crater, located on the north pole of the moon. Its walls enclose a ring of bright material as yet unexplained by science. Image: NASA / Jet Propulsion Lab.

 

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Oberon​

Little is known about Oberon, the outermost major moon of the planet Uranus. Consisting of approximately equal amounts ice and rock, Oberon appears to have been primarily shaped by asteroid and comet impacts. Image: NASA.

 

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Deimos​

The smaller of Mars' two moons, Deimos while still lumpy in appearance is less irregular in shape than its companion, Phobos. It's named after Deimos, the ancient Greek god and personification of dread and terror. Image: NASA/JPL-caltech/University of Arizona.

 

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Thebe​

Thebe bears the scars of a massive asteroid impact, the result of which is named the Zethus crater. This small, irregular shaped moon of Jupiter has had a hand in shaping the planet: dust ejected from its surface formed the Thebe Gossamer Ring around its gargantuan neighbor. Image: NASA/JPL.

 

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Proteus​

The second biggest moon orbiting Neptune after Triton, Proteus is one of the darkest objects in the solar system. Scientists theorize that Proteus might have been formed from debris as Triton was captured in Neptune's orbit. Image: Voyager 2, NASA.

 

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Ariel​

According to NASA, Ariel's surface appears to be the youngest of all the moons of Uranus. Its surface shows signs of more recent geological activity than other Uranian moons, most likely due to tidal heating—a process whereby orbital and rotational energy is dissipated as heat in either (or both) the surface ocean or interior of a planet or satellite. Image: NASA/JPL.

 

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Dactyl​

Rounding off this menagerie of moons is an alternative moon— Dactyl. It differs because it's the natural satellite to the asteroid Ida, located in the belt between Mars and Jupiter. Before its discovery, scientists had no evidence that asteroids could have moons.