Super Moons: Our Solar System's Mini Worlds

Earth and Various Moons to Scale

Some of the 160+ named moons in our solar system: Europa, Io, Ganymede, Callisto = Jupiter; Titan, Rhea, Enceladus, Iapetus, Dione, Mimas, Tethys = Saturn; Triton = Neptune; Titania, Miranda, Oberon = Uranus; Charon = Pluto.
Some of the 160+ named moons in our solar system: Europa, Io, Ganymede, Callisto = Jupiter; Titan, Rhea, Enceladus, Iapetus, Dione, Mimas, Tethys = Saturn; Triton = Neptune; Titania, Miranda, Oberon = Uranus; Charon = Pluto. | Source

Our Moon Is Not Alone

Our Earth's moon is big, beautiful, and special: it tickles us with tides, helps hold the planet steady to prevent climate-wrecking wobbles, and gave us the 24-hour-day by slowing down young Earth's hyperactive 6-hour rotation.

However, our moon is less unique than we thought. Ever since Galileo Galilee first gazed at Jupiter with his telescope in the 17th century and spotted the four big Jovian moons — Europa, Io, Ganymede and Callisto — we've known that other planets have moons, too.

When we started sending out space probes, we discovered many more moons. I remember being excited when the 1970s Voyager flybys pushed Jupiter's moon-count up into the 20s. Now, depending on what you count as a moon, Jupiter may have about seventy. Even little Pluto is now known to have at least five moons, and some asteroids have moons, too.

In fact, moonless Venus and Mercury and one-moon Earth appear to be the exception. So let's check out some of these bizarre mini-worlds that have been discovered in our own lifetimes!

It Ain't Pretty, but It's Colorful

What's cooking? Those big blotches are different kinds of sulfur lava flows from Io's many volcanoes. Io resurfaces itself continually; every few months scientists will see something different.
What's cooking? Those big blotches are different kinds of sulfur lava flows from Io's many volcanoes. Io resurfaces itself continually; every few months scientists will see something different. | Source

Io: Last One Is a Rotten Egg

Io, an inner moon of Jupiter, has been everybody's darling since the Voyager spacecraft first discovered active volcanoes on it in 1979. So what? Well, volcanoes should only pop up on planet-sized bodies with cores of molten rock. A little moon far out in the cold of space should've cooled to solid rock eons ago.

Before the Voyager probes, we thought that moons were boring, dead worlds like ours, an eerie airless desert of dust and old lavas where nothing ever happens unless a meteor plunks down. Boy were we wrong.

Io is like a piece of taffy caught in a three-way tug-of-war between the massive gravitational pull of Jupiter, Europa and the giant moon Ganymede. Just like kneaded pie dough, Io has heated up from the inside. Unlike pie dough, the inside is molten rock which explodes through the crust in enormous volcanic eruptions. Most of the material spewed out is sulfur, the same chemical that makes eggs yellow. Mixed with various compounds, the sulfur can turn rust red or blanch to white.

Io's volcanoes are almost always erupting plumes over a hundred miles into space. Some of this material surrounds Jupiter in a vast nebula.

Europa the Water World

Beautiful Europa may harbor a precious secret in the watery depths beneath its icy skin.
Beautiful Europa may harbor a precious secret in the watery depths beneath its icy skin. | Source

Europa: Jupiter's Icy Ocean Moon

The next moon out is Europa. It's so precious that NASA actually ordered the Galileo space probe on a kamikaze plunge into Jupiter at the end of its mission to make sure the craft never crashed into Europa. What's so special about Europa, that we didn't want to risk contaminating it with any microbes clinging to an aging robot?

It's an ocean world covered by a shell of ice. Just like Io, the tidal forces of Jupiter and the other moons keep Europa warm inside. Cracks covering Europa's surface show where the ice has broken. Slushy water squeezes out of these fissures onto the surface, where it refreezes.

Biologists have found that amino acids, the building blocks of life, are carried around our solar system in comets and asteroids. Their impact scars peck Europa's surface. We also know that liquid water is vital for life, at least on our planet: it readily dissolves and transports chemicals more efficiently than almost any other substance.

That's why scientists have rested their hopes on Europa, the most likely place in our solar system to harbor life outside Earth. Unlike Mars, whose surface is battered by solar radiation and too cold and dry for water to remain in liquid form, Europa's global ice cap protects the watery cradle within.

Below are snapshots of just a few of Jupiter's moons. It has dozens more, perhaps over a hundred, but most of them are just blobby asteroids.

Jovian Moons (Moons of Jupiter) Photo Gallery

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Jupiter and Io photographed by the New Horizons space probe to Pluto, passing by in 2007. (Jupiter is captured in infrared, which maps heat, so the Great Red Spot looks white). Note eruption plume on Io's pole (right).Red-hot lava flows on Io's surface. This is a closeup of the same eruption seen on the dark side of Io in the first snapshot of this gallery. More eruption plumes on Io taken in 1997.Icebergs of Europa. Tidal forces of Jupiter and other moons tugging on Europa causes flexing and cracking. Sometimes, icebergs shift and rotate, riding on slush that oozes to the surface.Ganymede is the largest moon in the solar system, larger than Mercury and Pluto, and three-fourths the size of Mars. It's a rocky world with a thin coating of ice chipped and cracked by meteor impacts, as well as -- surprisingly -- plate tectonics!Callisto is the last of the four "Galilean" moons discovered by astronomer Galileo Galilei in the 17th century. It's about the size of Mercury, another rocky world with a dusting of ice.Some of Jupiter's other moons: Thebe, Amalthea, Adrastea, and Metis. They're basically asteroids captured by Jupiter's gravity (you see why I call them "space potatoes"). Family portrait of Jupiter's four largest moons, the "Galilean" moons: Io, Europa, Ganymede, Callisto. Click link below for detailed info about each moon:Landscapes of the four Galilean moons: volcanic features; icebergs and ice fissures; grooves and ridges; impact craters. Click link below for more info:
Jupiter and Io photographed by the New Horizons space probe to Pluto, passing by in 2007. (Jupiter is captured in infrared, which maps heat, so the Great Red Spot looks white). Note eruption plume on Io's pole (right).
Jupiter and Io photographed by the New Horizons space probe to Pluto, passing by in 2007. (Jupiter is captured in infrared, which maps heat, so the Great Red Spot looks white). Note eruption plume on Io's pole (right). | Source
Red-hot lava flows on Io's surface. This is a closeup of the same eruption seen on the dark side of Io in the first snapshot of this gallery.
Red-hot lava flows on Io's surface. This is a closeup of the same eruption seen on the dark side of Io in the first snapshot of this gallery. | Source
More eruption plumes on Io taken in 1997.
More eruption plumes on Io taken in 1997. | Source
Icebergs of Europa. Tidal forces of Jupiter and other moons tugging on Europa causes flexing and cracking. Sometimes, icebergs shift and rotate, riding on slush that oozes to the surface.
Icebergs of Europa. Tidal forces of Jupiter and other moons tugging on Europa causes flexing and cracking. Sometimes, icebergs shift and rotate, riding on slush that oozes to the surface. | Source
Ganymede is the largest moon in the solar system, larger than Mercury and Pluto, and three-fourths the size of Mars. It's a rocky world with a thin coating of ice chipped and cracked by meteor impacts, as well as -- surprisingly -- plate tectonics!
Ganymede is the largest moon in the solar system, larger than Mercury and Pluto, and three-fourths the size of Mars. It's a rocky world with a thin coating of ice chipped and cracked by meteor impacts, as well as -- surprisingly -- plate tectonics! | Source
Callisto is the last of the four "Galilean" moons discovered by astronomer Galileo Galilei in the 17th century. It's about the size of Mercury, another rocky world with a dusting of ice.
Callisto is the last of the four "Galilean" moons discovered by astronomer Galileo Galilei in the 17th century. It's about the size of Mercury, another rocky world with a dusting of ice. | Source
Some of Jupiter's other moons: Thebe, Amalthea, Adrastea, and Metis. They're basically asteroids captured by Jupiter's gravity (you see why I call them "space potatoes").
Some of Jupiter's other moons: Thebe, Amalthea, Adrastea, and Metis. They're basically asteroids captured by Jupiter's gravity (you see why I call them "space potatoes"). | Source
Family portrait of Jupiter's four largest moons, the "Galilean" moons: Io, Europa, Ganymede, Callisto. Click link below for detailed info about each moon:
Family portrait of Jupiter's four largest moons, the "Galilean" moons: Io, Europa, Ganymede, Callisto. Click link below for detailed info about each moon: | Source
Landscapes of the four Galilean moons: volcanic features; icebergs and ice fissures; grooves and ridges; impact craters. Click link below for more info:
Landscapes of the four Galilean moons: volcanic features; icebergs and ice fissures; grooves and ridges; impact craters. Click link below for more info: | Source

Mini-Me Moon

Ida is the large asteroid — 36 x 14 miles — with little egg-shaped Dactyl (dot at right) 1 mile long.
Ida is the large asteroid — 36 x 14 miles — with little egg-shaped Dactyl (dot at right) 1 mile long. | Source

Dactyl, Orbiting Asteroid Ida

That Galileo spacecraft really gets around. On its way out to snoop on Jupiter for several years, it had to pass through the Asteroid Belt, so it took some snapshots of the asteroid Ida (the peanut-shaped rock at right) as it zoomed past.

To the surprise and delight of astronomers, they saw that Galileo had discovered the first moon orbiting an asteroid, just as the astronomer it was named for had discovered the first moons orbiting another planet.

Since little Dactyl was discovered, a few other asteroids have been found with moons — or more than a few, if you count "dwarf planets" like Pluto and Eris.

I think Dactyl is adorable, but there's just one problem. Dactyl is Greek for "finger" (compare pterodactyl, "wing-fingered"). Ida looks more dactyl-shaped to me than its little soccer ball companion.

[See a close-up photo of Dactyl on NASA's Ida & Dactyl page.]

A White Jewel of a Moon

Enceladus is a gorgeous ice moon where geological processes are continually resurfacing the landscape. It's one of my favorite objects in the solar system for its sheer beauty.
Enceladus is a gorgeous ice moon where geological processes are continually resurfacing the landscape. It's one of my favorite objects in the solar system for its sheer beauty. | Source

The Surface of Another World

It doesn't look like much, but this photo from the surface of Titan is our first landing on a world beyond Mars -- 887 million miles from the Sun. A smoggy methane haze dominates. Pebbles are actually water ice, the "rock" on Titan.
It doesn't look like much, but this photo from the surface of Titan is our first landing on a world beyond Mars -- 887 million miles from the Sun. A smoggy methane haze dominates. Pebbles are actually water ice, the "rock" on Titan. | Source

Enceladus, the Ice Geyser Moon

Enceladus, one of the innermost moons of Saturn, is like a cross between Jupiter's Europa and Io, but has a special beauty all its own. It's a tiny 310-mile-across ice world whose surface reflects almost 100% of sunlight that strikes it, making it one of the brightest objects in the solar system for its size.

Heating and squeezing from Saturn's gravity and the tug of other moons have resurfaced Enceladus so that it has only a few recent impact craters. Its southern hemisphere is striated with huge "tiger stripe" cracks that release plumes of ice from its interior.

These enormous geysers release vast quantities of water onto Saturn's cloud tops and into the area around Saturn, much in the way Io's volcanoes surround Jupiter with a faint sulfurous nebula. Scientists are having a field day analyzing what they describe as a dusty plasma, a very unusual state of matter, coming from Enceladus' plumes.

Titan, the Methane Moon

Massive Titan is the second largest moon in the solar system, orbiting Saturn. It's the only moon we know of with a substantial atmosphere, and more importantly, it's the only other moon where we've landed a spacecraft! As you'll see in the slideshow below, Titan's dense methane smog gives it the external appearance of a bland, featureless tan sphere. However, dig below the clouds with radar or infrared, and you're treated to an almost terrestrial landscape.

When the Cassini probe reached Saturn in 2004 for a four-year mission — which in fact is still ongoing! — it dropped off a mini Huygens lander through Titan's clouds to land on the surface. This was a daring thing to do, since some theories guessed that Titan had methane oceans. It doesn't have oceans, but it does have methane lakes, rivers, monsoon rains — in fact, everything that water does on planet Earth, liquid methane does on Titan. Unfortunately, it's so expensive to send equipment out to Saturn and back that it's not economically feasible to use Titan for all our natural gas needs.

Despite the flammable atmosphere and methane everywhere, Titan is very, very cold: water there is solid rock, and the moon's surface temperature is -290° F.

The Moons of Saturn

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Saturn's moon Titan, 3200 miles across, and Dione, 698 miles across, float against the backdrop of Saturn's cloud tops and rings. Look closely; you can see Titan's fuzzy atmosphere in front of Dione."That's no moon, it's a... oh, nevermind, it IS a moon." NASA scientists tend to refer to Mimas as the "Death Star moon" thanks to the 80-mile-wide impact crater that just barely failed to shatter it. (The moon Mimas is about 245 miles in diameter.)Saturn's moon Iapetus is a puzzle: its backside is light-colored, and its leading hemisphere is mostly coated with a muddy brown...something...that appears to have splattered it from another moon, the rings, or an unknown source.The moon Hyperion. Smaller bodies (it's 255 x 163 miles) don't have enough gravity to pull them into a spheroid shape; they tumble like space potatoes. Hyperion seems to be a loosely-packed sponge or honeycomb of dirty ice. Backlit ice geysers spew from Enceladus' southern limb, shooting plumes of frozen water hundreds of kilometers into space.False-color images taken in visible and infrared over the last several years show that Titan changes with the seasons: the poles develop brown caps, and huge dark lakes of methane fill at the tropics from monsoon rains. Light spots may be volcanic.River channels on Titan, and lowlands... are those dunes, or a lake? The amazing thing about Titan is that once you penetrate the clouds with radar (here) or infrared, it looks far more Earthlike than Mars.Surface of Titan: multiple photos snapped by Huygens from about 5 miles above the ground. A few white wisps of fog (?) hug an alien landscape scoured by wind and methane rains.Shepherd moons Prometheus (right, inside ring) and Pandora (left, outside ring) keep many of Saturn's rings in line. Or in this case, kinky. I remember when Voyager first discovered this ring, the F ring, whose "braided" shape puzzled scientists.
Saturn's moon Titan, 3200 miles across, and Dione, 698 miles across, float against the backdrop of Saturn's cloud tops and rings. Look closely; you can see Titan's fuzzy atmosphere in front of Dione.
Saturn's moon Titan, 3200 miles across, and Dione, 698 miles across, float against the backdrop of Saturn's cloud tops and rings. Look closely; you can see Titan's fuzzy atmosphere in front of Dione. | Source
"That's no moon, it's a... oh, nevermind, it IS a moon." NASA scientists tend to refer to Mimas as the "Death Star moon" thanks to the 80-mile-wide impact crater that just barely failed to shatter it. (The moon Mimas is about 245 miles in diameter.)
"That's no moon, it's a... oh, nevermind, it IS a moon." NASA scientists tend to refer to Mimas as the "Death Star moon" thanks to the 80-mile-wide impact crater that just barely failed to shatter it. (The moon Mimas is about 245 miles in diameter.) | Source
Saturn's moon Iapetus is a puzzle: its backside is light-colored, and its leading hemisphere is mostly coated with a muddy brown...something...that appears to have splattered it from another moon, the rings, or an unknown source.
Saturn's moon Iapetus is a puzzle: its backside is light-colored, and its leading hemisphere is mostly coated with a muddy brown...something...that appears to have splattered it from another moon, the rings, or an unknown source. | Source
The moon Hyperion. Smaller bodies (it's 255 x 163 miles) don't have enough gravity to pull them into a spheroid shape; they tumble like space potatoes. Hyperion seems to be a loosely-packed sponge or honeycomb of dirty ice.
The moon Hyperion. Smaller bodies (it's 255 x 163 miles) don't have enough gravity to pull them into a spheroid shape; they tumble like space potatoes. Hyperion seems to be a loosely-packed sponge or honeycomb of dirty ice. | Source
Backlit ice geysers spew from Enceladus' southern limb, shooting plumes of frozen water hundreds of kilometers into space.
Backlit ice geysers spew from Enceladus' southern limb, shooting plumes of frozen water hundreds of kilometers into space. | Source
False-color images taken in visible and infrared over the last several years show that Titan changes with the seasons: the poles develop brown caps, and huge dark lakes of methane fill at the tropics from monsoon rains. Light spots may be volcanic.
False-color images taken in visible and infrared over the last several years show that Titan changes with the seasons: the poles develop brown caps, and huge dark lakes of methane fill at the tropics from monsoon rains. Light spots may be volcanic. | Source
River channels on Titan, and lowlands... are those dunes, or a lake? The amazing thing about Titan is that once you penetrate the clouds with radar (here) or infrared, it looks far more Earthlike than Mars.
River channels on Titan, and lowlands... are those dunes, or a lake? The amazing thing about Titan is that once you penetrate the clouds with radar (here) or infrared, it looks far more Earthlike than Mars. | Source
Surface of Titan: multiple photos snapped by Huygens from about 5 miles above the ground. A few white wisps of fog (?) hug an alien landscape scoured by wind and methane rains.
Surface of Titan: multiple photos snapped by Huygens from about 5 miles above the ground. A few white wisps of fog (?) hug an alien landscape scoured by wind and methane rains. | Source
Shepherd moons Prometheus (right, inside ring) and Pandora (left, outside ring) keep many of Saturn's rings in line. Or in this case, kinky. I remember when Voyager first discovered this ring, the F ring, whose "braided" shape puzzled scientists.
Shepherd moons Prometheus (right, inside ring) and Pandora (left, outside ring) keep many of Saturn's rings in line. Or in this case, kinky. I remember when Voyager first discovered this ring, the F ring, whose "braided" shape puzzled scientists. | Source

Triton, the Frozen Cantelope Moon

Voyager 2 reached Neptune in 1989 and discovered wacky terrains on the surface of Triton, a moon 22% the size of ours.

This far out, most of the moons (and even the so-called gas giants) are mostly ice. Triton's surface is unique in the solar system: it's mostly nitrogen ice with methane ice caps. It also has ice volcanoes!

Surface of the Moon Triton (Orbiting Neptune)

The southern half of Neptune's moon Triton: a world in deep-freeze with "cryovolcanoes" and features that still puzzle scientists.
The southern half of Neptune's moon Triton: a world in deep-freeze with "cryovolcanoes" and features that still puzzle scientists. | Source

What's With the Warpaint?

Miranda is Latin for "ought to be wondered at," and we really wonder what happened to make that giant chevron-mark. The large "fingerprint" on the southern hemisphere is also a puzzle.
Miranda is Latin for "ought to be wondered at," and we really wonder what happened to make that giant chevron-mark. The large "fingerprint" on the southern hemisphere is also a puzzle. | Source

Miranda, Moon of Uranus

Uranus' moon Miranda has a name that means "wonderful," thanks to the bizarre giant chevron shape chipping its surface. This 300-mile-wide satellite doesn't seem large enough to have geological faulting, however, the alternate theory, that it was shattered multiple times by collisions and reassembled itself, seems even more fantastic. Scientists are still debating Miranda's complicated geology. (See that link for more photos of and information about this marvelous little moon.)

I remember staying up late to watch the Voyager 2 flyby of Uranus in 1986. When this picture slooooooowly arrived in mission control, there was a lot of head-scratching! (Yes, back then, we actually watched live coverage of space missions on late-night TV.)

By the way, if you pronounce "Uranus" the way classics majors are taught to pronounce Latin, you avoid various embarrassing pronunciations that cause students to titter. Class, try saying it this way: Oo-raaah-nus, with that middle syllable matching the "ah" sound of British English "father." Teachers, you're welcome.

Phobos and Deimos: The Doomed Moons of Mars

About 17 miles long, Phobos appears to be a captured asteroid circling Mars. In fact, it's caught in a death spiral: if Mars' gravity doesn't tear it apart into a ring, it will crash into the suface in ten million years.
About 17 miles long, Phobos appears to be a captured asteroid circling Mars. In fact, it's caught in a death spiral: if Mars' gravity doesn't tear it apart into a ring, it will crash into the surface in ten million years. | Source
Deimos is about 6-10 miles across (it's very irregular). Mars will eventually lose this moon, too: it's spiraling away. Phobos and Deimos are named after the sons of Mars in Greek and Roman mythology; their names mean "fear" and "panic."
Deimos is about 6-10 miles across (it's very irregular). Mars will eventually lose this moon, too: it's spiraling away. Phobos and Deimos are named after the sons of Mars in Greek and Roman mythology; their names mean "fear" and "panic." | Source

The Moons of Pluto

The Hubble Space Telescope has found most of Pluto's moons in 2011-2012. Moon P5, discovered on July 7 announced July 13, 2012, is a 6-to-15-mile "space potato."
The Hubble Space Telescope has found most of Pluto's moons in 2011-2012. Moon P5, discovered on July 7 announced July 13, 2012, is a 6-to-15-mile "space potato." | Source

The above photo is grainy, but the smallest two moons are 6 to 15 miles across, and it was taken by the long-past-its-expiration-date Hubble Space Telescope from how many gazillion miles away?

Hubble needs to stop making cool discoveries, or there will be nothing for the New Horizions spacecraft to discover when it reaches Pluto in 2015!

Actually, the fact that Pluto has been demoted to Dwarf Planet makes the New Horizons mission even more important, because it turns out that Pluto is one of several rocky mini-worlds ("dwarf planets" or "trans-Neptune Objects") orbiting out beyond Neptune in the Kuiper Belt, all of them pretty much unchanged since the solar system coalesced. Studying Pluto may give us insights into how the inner planets formed. I can't wait for the first pictures to come back. It's amazing that we've got a space probe that far out!

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Comments 6 comments

unknown spy profile image

unknown spy 4 years ago from Neverland - where children never grow up.

hi! I love your hub. this is very fascinating, very interesting to read.. i also kinda love their names.


CrawfsPlace profile image

CrawfsPlace 4 years ago from South Australia

Really interesting hub! You have a great writing style which keeps technical topics interesting to the reader. I love space and everything associated with it so you have a fan in me!


sandrabusby profile image

sandrabusby 4 years ago from Tuscaloosa, Alabama, USA

I always read your hub, Greekgeek, to see what I can learn. Thanks for the lovely images, too.


Ellen_Friedman 4 years ago

Excellent topic, beautiful collection of images. You've put poetry into the moons of our neighbors! Well done


fordie profile image

fordie 4 years ago from China

Fascinating. A lot of interesting facts supporting incredible photos. Will be looking up with different eyes tonight


Kristen Howe profile image

Kristen Howe 12 months ago from Northeast Ohio

Ellen, this was another wonderful hub from you on astronomy and our planets. This was so interesting to read about, right now.

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