10 Spectacular Moons in Our Solar System

Jupiter's Europa

This image details the frozen surface of Europa, one of Jupiter's estimated 69 known moons. Europa was named after a lover of Zeus, the Greek counterpart of Jupiter. NASA took this enhanced-color image from the Galileo spacecraft, which circled the largest planet on our solar system until 2003. NASA says the red lines are cracks and ridges are most likely created by the intense gravitational pull of Jupiter. As NASA writes, "Color variations across the surface are associated with differences in geologic feature type and location. For example, areas that appear blue or white contain relatively pure water ice, while reddish and brownish areas include non-ice components in higher concentrations." Europa is one of Jupiter's largest moons.

Europa's surface may also be covered in massive "ice spikes" as high as 50 feet tall, according to a 2018 study. The spikes would be similar to penitentes on Earth, which are snow formations found at high altitudes.

In order for these spikes to even form, "the ice must be sufficiently volatile to sublimate under surface conditions and diffusive processes that act to smooth the topography must operate more slowly," wrote the study's authors.

While there is no visual evidence of penitentes on Europa, scientists say radar and thermal data support the idea that conditions on Europa could allow for these ice spikes to form.

Neptune's Triton

This photo, taken by NASA through green, violet and ultraviolet filters, shows the bright southern hemisphere of Triton. Triton is named after the Greek sea god Triton, the son of Poseidon (the Greek god comparable to the Roman Neptune). Triton is the only Neptune moon that has an internal geology; it is known to have geological activity like geysers and volcanic activity. It is one of very few such moons in the solar system. Experts believe that Triton could have been a captured object from the nearby Kuiper Belt, where the dwarf planet Pluto and other objects reside. Triton is the largest of Neptune's moons and the only object that orbits any planet in a retrograde orbit. Just like our own moon, it is locked in a synchronous rotation with its home planet.

Jupiter's Io

Io is the closest large moon of Jupiter and was named for a priestess of Hera who became one of the lovers of Zeus. Io has the most volcanic activity of any moon in the solar system, and its entire surface is covered with lava every few thousand years. NASA notes that this photo is based on real infrared, green and ultraviolet-light images and has only been adjusted to show the contrast. Io has an irregular elliptical orbit and is slightly larger than our own moon. It was discovered in 1610 by Galileo.

Mars' Phobos

One of only two Martian moons, Phobos has been described as no more than a tiny rock. NASA also notes that Phobos is on a collision course with Mars. As NASA writes, "It is slowly moving towards Mars and will crash into the planet or break apart in about 50 million years." It has a six-mile gouge in it called the Stickney crater, which experts believe was caused by a meteorite impact. Phobos is named for one of the mythical sons of the Greek god Ares, who is the Greek equivalent of the Roman god Mars.

Jupiter's Ganymede

Ganymede is the largest moon in our solar system. In fact, it's bigger than the planet Mercury and the dwarf planet Pluto, and it is almost three-quarters the size of Mars. NASA explains that if Ganymede orbited the sun instead of Jupiter, it would be a planet. There is evidence of a thin oxygen atmosphere on Ganymede, but experts believe it is too thin to support life. Ganymede also sports a thin magnetic field, indicating that this moon can teach us a lot.

Uranus' Oberon

Oberon is named for Shakespeare's King of the Fairies from "A Midsummer Night's Dream." It is the second largest moon of Uranus, and was first studied when NASA's Voyager 2 flew by in 1986. This photo, taken by Voyager 2, shows "several large craters in Oberon's icy surface surrounded by bright rays similar to those seen on Jupiter's moon Callisto." Like the rest of Uranus' large moons, Oberon is mostly made of ice and rock. It was first discovered in 1787 by astronomer William Herschel. At present, Uranus has about 27 named moons.

Jupiter's Callisto

NASA reports that Callisto is the third largest satellite in the solar system and roughly the size of Mercury. Pictured here in color, NASA points out that its many markings show a turbulent history of collisions with space objects. In fact, Callisto is known to be the most heavily cratered object in our solar system. And while Callisto is uniformly cratered, it is not uniformly colored. Experts believe the different colors come from ice and ice erosion. It is the darkest of Jupiter's four largest moons, known as the Galilean satellites. But it is still twice as bright as our moon.

Saturn's Mimas

This color-enhanced view of Mimas from NASA shows a bluish band around the equator. Experts are unsure of the nature of this blue band, though NASA speculates it could have something to do with the high-energy electrons that drift in an opposite direction to the flow of plasma in the magnetic bubble around Saturn. As NASA reports, Mimas is named for a giant who was killed by Mars in the war between the Titans and the gods of Olympus. It is the smallest and innermost of Saturn's major moons. Some note that its giant impact crater makes it similar to the Death Star featured in the "Star Wars" series.

Earth's moon transiting the sun

Our moon is one of the largest satellites in the solar system, which is impressive considering how much smaller the Earth is compared to Jupiter or Saturn. It has a diameter of 2,160 miles, as opposed to 3,280 miles, the diameter of Jupiter's Ganymede, the largest satellite. Most experts agree that the moon formed when a Mars-sized planet collided with Earth several billion years ago. The ensuing debris cloud reformed into the moon. Here the moon is seen in a NASA composite image transiting the sun from the STEREO-B spacecraft.